A synthesis of RCTs on psychological interventions fostering strengths and virtues: Evidence from 21 systematic reviews

Abstract

Research on mental health advocates the cultivation of character strengths to enhance well‐being. Existing meta‐analyses support positive correlations between strengths and well‐being, and an increasing number of randomized controlled trials (RCTs) have assessed the effects of interventions aimed at cultivating them. This pre‐registered multiple systematic review of RCTs aims to map and synthesize evidence from these trials regarding the overall impact of such interventions on strengths and well‐being. Based on Peterson and Seligman's Virtues in Action model, which groups 24 character strengths under 6 virtues as latent variables, we conducted searches for each character strength (21 in total), across four specialized databases, including gray literature. The included RCTs assessed the impact of virtue‐based interventions with adult participants in studies including baseline and post‐intervention measures of the targeted strength and well‐being. After reviewing 61,479 abstracts, 162 RCTs were included representing 15 strengths grouped into the six virtues among 33,032 participants. In contrast, the interventions with the best evidence for increasing strengths and well‐being were those that enhanced kindness, humor, hope, perspective, and gratitude. Our review revealed that there is a relative paucity of RCT studies in the field and a need to include robust outcome measures. While there is relatively robust evidence of the efficacy of RCTs to enhance certain character strengths and associated well‐being, there is still insufficient evidence on the efficacy of most of the 24 strengths of Peterson and Seligman's model. We discuss implications of the findings and recommend guidelines for future research.

Scientific evidence has confirmed that psychological well‐being and its promotion cannot simply be reduced to the absence of suffering and psychopathology (Iasiello et al., 2020). Well‐being and psychopathology have a complex relationship, as they are not merely two ends of the same continuum (Keyes, 2002, 2005). This means that both individuals with and without mental health conditions can enhance their well‐being for a better quality of life. In this regard, psychological interventions should target well‐being promotion rather than just symptom improvement (Quoidbach et al., 2015; Vázquez, 2017). This approach has opened the doors to new types of psychological interventions, proactive rather than reactive, with the potential to be implemented in much broader settings than those aimed at reducing psychological suffering.

CULTIVATING VIRTUES AND ENHANCING WELL‐BEING

Influential theoretical models of well‐being converge on a two‐dimensional structure composed of the hedonic and the eudaimonic dimensions (Huta & Waterman, 2014). The hedonic dimension embodies the pursuit of pleasure and the avoidance of pain. This dimension is well represented by the concept of subjective well‐being (SWB), which adds the cognitive element of life satisfaction to the affective component (Diener, 2000). The eudaimonic dimension, in contrast, involves the realization of human potential and is represented by what Carol Ryff coined as psychological well‐being (PWB; Ryff, 1989). These two dimensions should not be seen as independent or antagonistic elements. From an integrative perspective, Sheldon (2016) proposed the Eudaimonic Activity Model, which suggests that eudaemonia is not accurately conceptualized as a form of well‐being and makes much more sense as a “cause” or “pathway” to achieve well‐being. According to this model, engaging in eudaimonic actions or virtues that promote growth helps people satisfy basic psychological needs like sense of competence, autonomy, and relatedness (Ryan & Deci, 2017), which ultimately results in greater well‐being.

While there is some consensus on the hedonic dimension of well‐being, and there is robust programmatic research on its psychological and neuroscientific components, there is less agreement on the conceptualization of the eudaimonic dimension. Conceptualizations range from general (e.g., orientations, values, motives, or goals) to more specific aspects (e.g., characteristics and contents of behavior, cognitive‐affective experiences, and forms of functioning) (Huta & Waterman, 2014). For example, Fowers (2012) described eudaimonic activities as those with intrinsic value and meaning, consistent with one's own values, commitments, and identity. According to this model, specific behaviors like altruism, gratitude, forgiveness, helping others, or being compassionate could positively impact PWB. All these “eudaimonic activities” can also be conceptualized as actions guided by virtues.

Psychological interventions that focus on the eudaimonic dimension often include strategies based on virtues (Huta & Waterman, 2014). Virtues can be understood as motivational tendencies and behavioral dispositions that characterize the individual and are valued positively across cultures (Peterson & Seligman, 2004). Traditionally, virtues encompassed all aspects that made a person admirable or outstanding (e.g., in ancient Greece, the term for virtue ‐arete‐ was more aligned with excellence than with moral goodness; McGrath, 2021). In recent years, scientific endeavors have increasingly focused on the study of traits and behaviors related to virtues (kindness, gratitude, zest, etc.) (Fowers et al., 2021).

The most widely recognized model of psychological virtues is the Virtues in Action (VIA) model (Park et al., 2004; Peterson & Seligman, 2004), a taxonomic framework that identifies six major virtues expressed through 24 character strengths. They are considered as trait‐like and possibly universal positive features that reflect the “excellent” aspects of an individual's personality, and are expressed as capacities for thinking, feeling, and behaving in ways that benefit both the individual and others, such as kindness, perspective‐taking, or forgiveness. In this model, virtues function as latent variables expressed through these strengths.

The conceptual framework of strengths and virtues opens up the possibility of creating an evidence‐based map of positive human qualities. Furthermore, it also facilitates using this map as a compass for designing psychological interventions that can enhance these qualities. When addressing the question of whether character strengths can be trained or cultivated, interventions can be classified into four typologies: a) providing knowledge or conceptualization; b) encouraging recognition; c) promoting action through training, and d) fostering reflection on one's own or others' use of strength (Lavy, 2020). Recently, Jankowski et al. (2020) introduced the concept of virtue‐based interventions (VBIs). These authors defined VBIs as psychological or behavioral programs that, despite employing different strategies, share the notion that increased participation in eudaimonic activities fosters the development of psychological mechanisms underlying the enhancement of well‐being. Some of the included interventions are positive psychology interventions and programs based on mindfulness and compassion, among others (Jankowski et al., 2020).

However, understanding whether VBIs increase well‐being through the cultivation of a target virtue remains challenging. This difficulty arises from the absence of a systematic mapping of the available evidence, and prioritizing the most robust study designs (i.e., RCTs) to address this question. These types of design can help to overcome some of the above‐mentioned limitations. First, RCTs are considered the gold standard for evaluating the effectiveness of psychological interventions due to their ability to minimize biases and establish potential causal relationships (Higgins et al., 2019). Second, by randomly assigning participants to either an intervention group or a control group, RCTs ensure that differences in strengths and related outcomes can be attributed to the intervention rather than confounding variables, which enhances internal validity. Third, RCTs typically incorporate blinding and standardized protocols, which reduce observer and participant biases, further strengthening the reliability of findings (Boutron et al., 2019). Overall, the methodological rigor of RCTs makes them unparalleled in generating high‐quality evidence despite their potential biases (Mohr, 2024) and allows for replication and evidence synthesis, essential for paving the way for evidence‐based psychological interventions (Cuijpers et al., 2016). We firmly believe that a review of RCT studies can be an accurate means to better gauge the efficacy of psychological interventions in the burgeoning and relatively new field of psychological strengths. Some metanalysis has shown the effects of character strengths training on specific strengths, for example, the effect of loving‐kindness meditation over self‐compassion (Reilly & Stuyvenberg, 2023) or gratitude interventions over gratitude strength (Diniz et al., 2023), but there are few compared with those focused on the outcomes. This review aims to map and synthesize, for the first time, the overall evidence from RCTs on the impact of VBIs on character strengths and the associated effects on well‐being. Our research question is: Is there evidence that VBIs enhance character strengths and well‐being?

METHODS

Outcome measures

The outcomes of interest were those assessing strengths and virtues, and psychological well‐being. The conceptual framework utilized for virtue selection and modeling followed the VIA model (Park et al., 2004; Peterson & Seligman, 2004). In this model, virtues are seen as latent factors that express observable character strengths. We conducted one systematic review for each strength. However, to operationalize them, we implemented minor modifications to the VIA model strengths, as there is some overlap in the description of the strengths (e.g., the term “kindness” appears in the description of three strengths; https://www.viacharacter.org/). The modifications were as follows: fairness was merged with kindness, curiosity with love of learning, and judgment with prudence. Given that many of these terms were not easily converted into keywords or do not exist as an area of research, we utilized proximal constructs as keywords, which we obtained from the definitions reported by Peterson and Seligman (2004). For example, for kindness, the terms “compassion”, “self‐compassion”, and “kindness” were included in the search (Supplementary Materials). For psychological well‐being, we considered any measures of hedonic or eudaimonic well‐being.

Study search and selection

For each of the modeled strengths, we conducted searches in PsycINFO, Web of Science, Scopus, and PubMed from inception, with the initial search in June 2023 and an update in May 2024, using database‐specific search strategies. Additionally, we screened references from relevant literature for eligible studies. We included articles published in English and Spanish, as well as gray literature such as theses or dissertations. Studies were deemed eligible if: (1) they were RCTs (clinical or community‐based); (2) the intervention was specifically designed to modify a virtue or character strength; (3) VBIs were conducted over at least two days, excluding lab inductions; (4) included adult participants (over 18 years old) (5) with no cognitive impairment; and (6) included baseline and post‐intervention specifically designed to measure the targeted strength and well‐being.

There was a two‐step study selection process. First, we screened titles and abstracts. Full texts were retrieved for records that were not excluded, and a second selection round was conducted by reviewing the full articles. Study selection was conducted by a team of independent investigators (PS, JN, and JV), and any disagreements were resolved by a third senior reviewer (AC) until consensus was reached. Inter‐rater agreement was calculated (Supplementary Materials).

Data extraction and risk of bias assessment

Data from the included studies were extracted independently by two reviewers (JV and PS). Discrepancies were resolved by discussion with a third senior reviewer (AC). Data extraction involved the use of a pre‐specified spreadsheet including sample demographics (gender, average age, educational level, etc.), study design (sample size, type of control group, etc.), intervention features (type of intervention, model of delivery, duration, etc.), and outcome measurement (instrument used, reliability and validity). Risk of bias in the included studies was assessed by two independent reviewers using the Cochrane Collaboration's risk of bias assessment tool RoB 1.0.

Transparency and openness

The methods followed for this study were fully pre‐registered (PROSPERO 2023 CRD42023381803, accessible at https://www.crd.york.ac.uk/PROSPERO/view/CRD42023381803). Pre‐registration was amended in September 2024 to update the search date. There were some deviations from the registered protocol. Initially, we specified in the protocol that one of the inclusion criteria required the used instrument to measure strengths and well‐being to be psychometrically validated. However, this criterion proved difficult to meet in practice, so we had to relax it. Ultimately, we accepted studies that used reliable, theory‐driven measures. The quality of the studies was evaluated and analyzed, including the quality of the instruments chosen. We adhered to the PRISMA guidelines for reporting systematic reviews (Moher et al., 2009; Page et al., 2021). All data and research materials (including our coding scheme) are available at [https://osf.io/gv3bc/].

Data synthesis

Data synthesis was qualitative, aimed at mapping the available evidence. The work reported herein organizes and synthesizes all the gathered evidence. Data were arranged in tabular format, grouping similar studies by character strength and virtue, and further categorized by whether the control group was passive or active. Descriptive statistics (e.g., frequencies and percentages) were extracted for specific aspects of the studies (e.g., the volume of studies by strengths at each stage of the screening process).

Study sample and design characteristics

Studies from the six virtues classified in the VIA were included (Table S1). However, only 15 character strengths met the inclusion criteria to be included in the analyses. A total of 162 papers were included, totaling 33,032 participants. Study sample sizes ranged from n = 19 (Adelstein, 2016) to n = 4,786 (Ho et al., 2024). The countries where the most studies were conducted were, in descending order, the USA (k = 52), China (k = 10), the Netherlands (k = 10), the UK (k = 9), and Spain (k = 9). Only 17.2% (k = 28) of the studies were conducted in non‐Western countries (Supplementary Materials). In 73.5% of the studies (k = 119), the sample was non‐clinical, while 17.9% (k = 29) of the studies involved participants with physical illnesses, and 8.6% (k = 14) involved participants with various psychological conditions. The oldest study dated back to 2003, indicating the relative novelty of the field. The most frequently used instruments for measuring well‐being were the Positive Affect subscale from the Positive and Negative Affect Scale (PANAS; Watson et al., 1988) (21.5%), the Satisfaction with Life Scale (SWLS; Diener et al., 1985) (18.6%), and the WHO‐5 Well‐Being Index (World Health Organization, 1998) (9.6%). Only 18 (11.1%) of the studies reported the use of eudaimonic well‐being measures. The tested interventions were trainings, ranging in duration from two days to nine months. Active controls (k = 101; 62.3%) generally consisted of daily activities, not designed to modify either the target strength or well‐being (for information on each study's active control group, see Supplementary material).

RESULTS

Figure 1 (Section A) shows a unified study selection flowchart including the 21 systematic reviews (specific flow charts for each review are available in the Supplementary Materials). A total of 61,479 records were assessed. The strength for which the most records were found was hope (n = 10,968) whereas humility showed the fewest number of records (n = 196). The strength for which most trials were finally included was kindness, with 38 trials. In contrast, no trials for curiosity, honesty, justice, perseverance, or creativity met the selection criteria. The main reasons to exclude a study were: not being a RCT design (33.4%), the intervention was not designed specifically to foster a strength or a virtue (20.8%), did not include any well‐being measure (18%), did not include any measure of strengths (10.9%), or the intervention was merely a lab induction (5.6%) (Figure 1).

FIGURE 1.

Study selection flowchart. One search was conducted per strength. Records were aggregated across strengths for this flowchart, with ranges representing the smallest and largest numbers within individual strengths. STG = Strength.

Systematic reviews of character strengths and virtues

In total, 107 studies (66%) reported successful increases in the specific strengths targeted by the intervention, while 102 studies (62.9%) reported being effective in enhancing well‐being (53% when compared to active controls, and 75% when compared to passive controls). The studies that were effective in increasing both the strength and well‐being were 83 (51.2%), with 19 (11.7%) reporting effective increases only in well‐being (but not the strength), 24 (14.8%) only increasing the strength (but not well‐being), and 36 (22.2%) reporting no significant effects in any of the measures (Table 1).

TABLE 1.

Main characteristics of the trials included.

Author	Country	n	Participants	Mean age (SD)	Intervention	Comparator	Strength outcome	Wellbeing outcome	Follow‐ups
APPRECIATION OF BEAUTY AND EXCELLENCE
Martinez‐Martí et al., 2018	Spain	240	1	32.09 (10.97)	Intervention to cultivate some attitudes toward the social or physical environment	G1. Placebo G2. WL	ABES	SPANE‐P	1 month
BRAVERY
Hagberg et al., 2023	Sweden	210	1	42.00 (9.00)	G1. Unguided self‐help G2. Guided self‐help	WL	AAA‐S; RASa	QWB	1 year
de Sousa & da Costa Padovani, 2021	Brazil	25	1	19.68 (3.62)	G1. Rational emotive behavior therapy G2. Psychoeducation on interpersonal rights, in assertive skills, and subjective well‐being	Non‐active	ISS‐Coping and Self‐affirmation with risk	LSSa; PANAS‐PA	6 weeks
FORGIVENESS
Ho et al., 2024	USA	4,786	1	26.00 (ND)	REACH Self‐directed forgiveness workbook intervention	WL	DFS; FS‐SH; TFS; TRIM‐18	SFI	2 weeks
Rye & Pargament, 2002	USA	58	1	18.80 (1.10)	Secular forgiveness intervention	Non‐active	FSa	SWBS‐Existential	6 weeks
Standard, 2004	USA	70	1	38.60 (ND)	Cognitive‐based forgiveness intervention	WL	HFS; FSES	PANAS‐PA	6 weeks
Toussaint et al., 2020	USA	124	1	23.00 (1.44)	REACH forgiveness programme	WL	Decisional Forgiveness Scale; EFS; TRIM‐18	PANAS‐PA	4 weeks
Zhang et al., 2014	China	31	1	22.10 (.98)	Forgiveness Intervention based on the Chinese version of Enright's model	G1. Interpersonal psychotherapy G2. Non‐active	SCF	Index of Well‐Being & Index of General Affect	4 weeks
GRATITUDE
Adelstein, 2016	USA	19	2	32.7 (ND)	Gratitude journal	WL	GQ‐6	PANAS‐PA PWS	1 month
Bohlmeijer et al., 2021	Netherlands	217	1	48.6 (9.60)	Writing exercises, psychoeducation, reflection	Self‐kindness intervention	GQ‐6	MHC‐SF	6 weeks and 6 months
Chan, 2013	China	81	1	33.73 (7.15)	Counting blessings	Counting misfortunes	GAC	PANAS‐PA; SWLS	No follow‐ups
Condon, 2022	USA	38	2	67.53 (9.44)	Gratitude journal	Non‐active	GQ‐6	FSb	No follow‐ups
Datu et al., 2022	China	129	1	20.27 (1.10)	Gratitude list	G1. List five acts of kindness G2. List five academic or work activities that were accomplished	Values‐in‐Action Youth‐Inventory‐Gratitude subscale	RLSS; SPANE‐P	No follow‐ups
Deng et al., 2019	China	104	1	35.49 (9.65)	G1. Counting Blessings G2. Sharing gratitude	To read a short essay concerning technology and summarize it every night	GRAT	Composite of SWLS and SPANE‐P	No follow‐ups
Emmons & McCullough, 2003 (Study 3)	USA	65	2	49 (ND)	Gratitude journal	Non‐active	A composite measure of gratitude‐related words	PAL	No follow‐ups
Gavian, 2011	USA	247	1	Range: 18–21	Gratitude journal	G1. Progressive muscle relaxation G2. Describe daily schedule	GQ‐6	PANAS‐PA; SWLS	1 month
Goerling, 2017	USA	352	1	ND	G1. Private Facebook gratitude writing G2. Public Facebook gratitude writing	To write out several activities they completed that day and post them publicly on Facebook	GQ‐6	PANAS‐PA; SWLS	1 month
Gold et al., 2023	USA	223	1	40.5 (ND)	Three good things	Non‐active (delayed gratitude activity)	GAC	PANAS‐PA; SWLS	3 months
Hames, 2015	USA	192	3	20.36 (5.08)	Gratitude journal	G1. Priorities intervention: List up to five of their priorities for the next day G2. Non‐active	GQ‐6	SHSa; SWLS	1 and 2 months
Henrie, 2006	USA	136	1	46.60 (4.26)	Writing gratitude exercise	G1. Psychoeducation about happiness, resilience, and well‐being G2. Waitlist	GQ‐6	SWLS	No follow‐ups
Herd, 2021	USA	57	1	ND	Gratitude journal	Any event diary	GAC	PANAS‐PA	No follow‐ups
Hodge, 2016	USA	33	1	ND	Gratitude journal	Any event diary	A composite measure of gratitude‐related words; GQ‐6	IHMH; PANAS‐PA; SWLS	No follow‐ups
Işık & Ergüner‐Tekinalp, 2017	Turkey	21	1	18.19 (2.47)	Gratitude journal	WL	GQ‐6	PANAS‐PA; SWLS	No follow‐ups
Kerr et al., 2015	Australia	48	3	43.00 (11.10)	Gratitude list	Mood‐monitoring placebo control	A composite measure of gratitude‐related words	PANAS‐PA	No follow‐ups
Kloos et al., 2022	Netherlands, Belgium	849	1	52.90 (14.50)	Gratitude app	WL	A composite measure of gratitude‐related words; GQ‐6	MHC‐SF	6 weeks
Koay et al., 2020	India	42	1	21.79 (2.19)	Social media‐based gratitude intervention	To post any image related to colors to describe their feelings, thoughts, and life events	GQ‐6	SWLS	No follow‐ups
Krentzman et al., 2015	USA	23	3	46.30 (10.9)	Three good things	Placebo sleep hygiene questions	GQ‐6	PANAS‐X‐APA; PANAS‐X‐UPA	8 and 14 weeks
Lee et al., 2023	Netherlands	133	1	32.75(12.82)	Gratitude diary, grateful contemplation, and behavioral expression of gratitude	Chatbot about films	GQ‐6	SPANE‐P	No follow‐ups
Li et al., 2021	China	415	2	ND	G1. Three good things with electronic social networking G2. Three good things	Psychoeducation about mental health promotion	GQ‐6	PANAS‐PA; SHSa	3, 6, and 12 months
Linley et al., 2013	UK	280	1	18.95 (1.11)	Three good things	Neutral writing task	GQ‐6	PANAS‐PA	No follow‐ups
Martínez‐Martí et al., 2010	Spain	159	1	20.70 (1.48)	Gratitude journal	G1. Hassles diary G2. Any event diary	A composite measure of gratitude‐related words	PAL; Subjective well‐being	2 weeks
Nawa & Yamagishi, 2021	Japan	84	1	21.75 (1.48)	Gratitude journal	WL	GQ‐6	SWLS	1 and 3 months
O'Connell et al., 2017	Ireland	135	1	27.08 (12.63)	G1. Reflective interpersonal gratitude journal G2. Reflective‐behavioral interpersonal gratitude journal	To write things that happened during the day	GQ‐6	SWLS	1 and 3 months
O'Connell et al., 2018	Ireland	91	1	23.61 (7.79)	G1. Interpersonal gratitude journal G2. Traditional gratitude journal	Experiential writing	GQ‐6	SWLS	1 month
Park, 2015	USA	245	1	ND	Gratitude journal	G1. Hassles diary G2. Life details diary	GQ‐6; GRAT	PANAS‐PA; SHSa	No follow‐ups
Peng et al., 2022	China	124	1	26.17 (4.89)	Gratitude list	To practice calligraphy and follow the samples shown in the copybook for 15 min before going to bed	GQ‐6	PANAS‐PA; SWLS	No follow‐ups
Regan et al., 2023	Australia	958	1	47.80 (16.90)	G1. Social gratitude letters G2. Nonsocial gratitude letters	Writing about daily activities	Gratitude Composite: GQ‐6 + MCGM	SWLS	1 week
Renshaw & Hindman, 2017	USA	115	1	20.56 (1.92)	Instant gratitude notes	G1. Social control: Sending notes to others regarding something they learned recently G2. Nonsocial control: Journaling about something they learned recently	GQ‐6	SWLS	No follow‐ups
Renshaw & Rock, 2018	USA	97	1	19.91 (1.99)	Gratitude thinking	Think about something they had learned recently	GQ‐6	PANAS‐PA; SHSa; SWLS	No follow‐ups
Srivastava & Ghosh, 2023	India	80	1	Range:18‐29	Three good things + Gratitude letter exercises	Non‐active	GQ‐6	SHSa	No follow‐ups
Tolcher et al., 2022	USA	132	1	19 (1.00)	G1. Gratitude journal G2. Gratitude reflection G3. App prompted gratitude reflection	Free journaling	GQ‐6	OHQ; SWLS; PANAS‐PA; WHO‐5	No follow‐ups
Tricarico, 2012	USA	160	1	43.00 (11.00)	Counting blessings	Non‐active	GAC; GQ‐6	PANAS‐PA; SWLS	1 month
Walsh et al., 2023	USA	916	1	19.40 (2.10)	Writing gratitude letters	Track daily activities	GQ‐6	CIT; AAS‐PA	No follow‐ups
HOPE
Carrillo et al., 2021	Spain	112	1	21.76 (3.63)	Best possible self	Writing down and visualizing the previous day	LOT‐R	HM; PANAS‐PA	No follow‐ups
Dennis & Ogden, 2022	UK	205	1	26.29 (12.25)	Best possible self	G1. Writing a summary of a TV plot G2. Nostalgia group: Thinking of a nostalgic event G3. Gratitude group: Thinking of three things for which you are grateful today	LOT‐R	SHSa	1 week
Enrique, Bretón‐López, Molinari, Baños, & Botella, 2018	Spain	81	1	23.80 (3.85)	Best possible self	Thinking and writing about the previous day	LOT‐R; SPT‐positive	PANAS‐PA	3 months
Enrique, Bretón‐López, Molinari, Roca, et al., 2018	Spain	59	3	27.10 (8.60)	Best possible self	Writing about daily activities	LOT‐R	PANAS‐PA	1 and 3 months
Heekerens et al., 2020	Germany	188	1	22.35 (5.04)	Best possible self	Writing and imagining the previous day	FEX	PANAS‐PA; SWLS	1 week
Littman‐Ovadia & Nir, 2014	Israel	90	1	28.10 (6.87)	Thinking of three good things waiting for you tomorrow	Thinking of three things for tomorrow	LOT‐R	PANAS‐PA; SWLS	1 month
Meevissen et al., 2011	Netherlands	54	1	23.50 (6.39)	Best possible self	Imagining daily activities	ASQ; LOT; SPT‐positive	PANAS‐PA	No follow‐ups
Mohammadi et al., 2018	Iran	62	2	52.60 (5.40)	Optimism training programme	Cardiovascular education	LOT‐R	OHI; PANAS‐PA; SWLS	16 weeks
Molinari et al., 2018	Spain	80	2	51.08 (10.54)	Best possible self	Thinking and writing about the previous day	LOT‐R	PANAS‐PA	1 and 3 months
Murdoch et al., 2020	Canada	35	2	66.45 (9.46)	Strength, hope, and resourcefulness programme	WL	HHI	MHC‐SF	6 weeks
Murphy et al., 2015	UK	81	1	67.15 (5.90)	Positive Imagery Training	Auditory and picture‐word sessions without imagery component	LOT‐R	PANAS‐PA	1 month
Nicolson et al., 2020	Netherlands	66	1	21.20 (2.48)	Best possible self	Writing about daily activities	LOT‐R	PANAS‐PA	No follow‐ups
Peters et al., 2013	Netherlands	90	1	22.80 (6.40)	Best possible self	Imagining details of everyday occurrences	LOT‐R	SWLS	1 week
Sergeant & Mongrain, 2014	Canada	466	1	32.75 (12.23)	Listing five things that make life enriching and 3 things to see the bright side of a difficult situation, and describe a goal and the steps to achieve it	Writing about the previous day and describing what they think the next day will be like	LOT‐R	OTH; SWLS	1 and 2 months
Tomczyk et al., 2023	Germany	391	1	28.83 (13.25)	G1. Best Possible Self G2. COVID‐19‐specific Best Possible Self	Thinking and writing about the previous day	LOT‐R	PANAS‐PA; SWLS	2, 3 and 4 weeks
HUMILITY
Liu et al., 2022	USA	75	1	37.96 (11.43)	Quiet Ego Intervention	Listening to an audiobook	QES	MHC‐SF	No follow‐ups
Wayment, Collier, et al., 2015	USA	32	1	18.16 (0.45)	G1. Quiet Ego Contemplation G2. Quiet Ego Contemplation with virtual reality	Reading National Geographic magazines	QES	PAVAS	No follow‐ups
HUMOR
Linge‐Dahl et al., 2023	Germany	140	2	64.48 (14.09)	“Humorous visit” in the hospital	Non‐active	STCI‐Cheerfulness	SWLS	No follow‐ups
Proyer et al., 2021	Germany, Switzerland, USA	1,275	1	43.76 (12.67)	G1. Thinking about three playful things and writing about them G2. Using playfulness and writing about playful things G3. Reflecting on playful experiences and write about them	Writing about early memories	OLIW‐playfulness questionnaire	AHI	2, 4 and 12 weeks
Ruch et al., 2018	Switzerland	110	1	47.53 (11.75)	Humor training	G1. Placebo humor group G2. WL	Sense of Humor Scale; STCI‐Cheerfulness	SWLS	2 months
de Sousa et al., 2019	Portugal	70	2	ND	Visualization of humor movies	Visualization of neutral movies	MSHS	SHSa; SWLG	No follow ups
Tagalidou, Baier, & Laireiter, 2019	Austria	182	1	24.91 (8.22)	G1. Coping humor G2. Three funny things	G1. Writing about early memories G2. Three good things	CHS; STCI‐Cheerfulness	AHI	1 month
Tagalidou, Distlberger, et al., 2019	Austria	37	3	50.86 (13.68)	Humor training	WL	CHS; STCI‐Cheerfulness	WHO‐5	1 month
Wellenzohn et al., 2018 (Study 2)	Germany, Switzerland	1,472	1	47.38 (11.55)	Three funny things	Writing about early memories	SHSb	AHI	1, 3 and 6 months
KINDNESS
Al‐Refae et al., 2021	Canada	245	3	25.24 (8.74)	Mindfulness and self‐compassion‐based cognitive smartphone intervention	WL	SCSa	PWS	No follow‐ups
Andersson et al., 2022	Sweden	49	1	Range: 25–55	Compassion‐focused therapy + Mindfulness and self‐compassion	Physical exercise	SCSA	SWLS	3 months
Arimitsu, 2016	Japan	40	1	21.34 (4.24)	Enhance self‐compassion	WL	SCSA	MMS‐PE	3 months
Bolognino et al., 2023	USA	52	1	Range: 18–22	G1. Loving‐kindness meditation G2. Mindful breathing meditation + loving‐kindness meditation	G1. Relaxation control G2. Mindful breathing meditation	SCBCS; SCS‐SF	PANAS‐PA	No follow‐ups
Brenton‐Peters et al., 2024	New Zealand	249	1	42.49 (11.18)	Weight watchers + The self‐compassion for weight management intervention	Weight watchers	SCSa	WHO‐5	12 weeks
Brito‐Pons et al., 2018 (Study 1)	Chile	50	1	38.06 (12.38)	Compassion cultivation training	WL	CS; SCSa	SHSa; SWLS	2 months
Gaiswinkler et al., 2020	Austria	249	3	48.45 (8.60)	Mindfulness and self‐compassion	Progressive muscle relaxation	SCSa	Single‐item happiness report	No follow‐ups
Gammer et al., 2020	UK	206	1	35.19 (4.00)	Kindness for mums online	WL	SCSa	WEMWBS	6 weeks
Guo et al., 2020	China	314	1	30.60 (5.95)	Mindfulness and compassion with self and others	WL	SCSa	WHO‐5	1 year
Guo et al., 2024	China	64	3	20.26 (1.63)	Compassionate mind training + CBT	WL	SCSa	GWBS	4 months
Haley et al., 2022	USA	34	1	37.80 (12.10)	Self‐compassion intervention	WL	SCS‐SF	PANAS‐PA	1 month
Hansen et al., 2021	Denmark	161	1	52.60 (12.50)	Compassion cultivation training	WL	MCS; SCSa	WHO‐5	3 and 6 months
Haydon et al., 2023	USA	133	2	62.65 (6.39)	G1. Acts of kindness to others G2. Acts of kindness to self G3. Self‐kindness meditation	Daily‐activity‐writing control	SCS‐Self kindness	MHC‐SF	No follow‐ups
Kariyawasam et al., 2023	UK	477	1	Range: 18‐64	Compassionate mind training	G1. Waitlist‐Sri Lanka G2. Waitlist‐UK	CEAS	WEMWBS	2 weeks
Kirby et al., 2023	Australia	102	1	38.31 (5.10)	Compassion‐focused therapy	WL	CEAS	WEMWBS	3 months
Kolchraiber et al., 2022	Brazil	65	1	37.00 (14.96)	Cognitively based compassion training	Several activities (physical activities, art workshops, reading, cooking, permaculture, and conversation circles)	SCSa	PANAS‐PA	3 months
Krieger et al., 2019	Switzerland	144	1	37.60 (11.50)	Mindfulness‐based compassionate living	TAU	SCSa	SWLS	6 months
Kropp et al., 2019	Germany	147	1	24.02 (4.52)	Loving kindness meditation	G1. Breathing meditation G2. Body scan	Self‐Compassion Scale‐34‐D	SWLS	No follow‐ups
Lang et al., 2019	USA	37	3	49.10 (14.50)	Adaptation of cognitively‐based compassion training	Veteran.calm, a “mind–body intervention” that focuses on relaxation	SCSa	SWLS	No follow‐ups
Leboeuf et al., 2022	France	227	1	34.50 (14.75)	Compassionate mind training	WL	SCSa	PWS	1 month
Linford & Warren, 2024	USA	461	1	26.60 (10.40)	Gift of self‐compassion	Expressive writing	SCSa	PANAS‐PA; SURF; SWLS	No follow‐ups
Mak et al., 2018	China	2,161	1	33.64 (12.08)	Self‐compassion programme	G1. Mindfulness‐based program G2. Cognitive behavioral psychoeducation control	SCSa	WHO‐5	3 months
Matos et al., 2017	Portugal	117	1	23.34 (4.16)	Compassionate mind training	WL	CEAS	TPAS	No follow‐ups
Matos et al., 2022	Portugal	155	1	51.30 (7.24)	Compassionate mind training	WL	CEAS	TPAS	3 months
Mifsud et al., 2021	Australia	79	2	58.60 (10.53)	G1. Web‐based self‐compassion focused writing activity (My Changed Body‐MyCB) G2. MyCB + Meditation combined	Expressive writing	SCA	PANAS‐PA	1 month
Müller‐Engelmann et al., 2024	Germany	32	3	36.94 (13.46)	Cognitive techniques with loving‐kindness meditations	WL	SCSa	WHO‐5	No follow‐ups
Neff & Germer, 2013 (Study 2)	USA	54	1	50.10 (11.43)	Mindfulness and self‐compassion	WL	CS; SCSa	SHSa; SWLS	6 months and 1 year
O′Hare & Gemelli, 2023	USA	72	1	22.90 (6.88)	Self‐compassion mindfulness meditation	Focused attention	SCSa	PANAS‐PA	No follow‐ups
Polizzi et al., 2022 (Study 2)	USA	131	1	18.96 (1.00)	G1. Lovingkindness meditation‐self G2. Lovingkindness meditation‐other G3. Lovingkindness meditation‐self and other	Sitting quietly	CLH; SCS‐SF	PANAS‐PA	2 weeks
Rojas et al., 2023	Spain	44	1	23.40 (5.59)	Compassion cultivation training	WL	CSP; SCS‐SF	PHI	2 months
Shahar et al., 2015	Israel	38	1	30.62 (10.50)	Loving kindness meditation	WL	SCSa	PANAS‐PA	3 months
Smeets et al., 2014	Netherlands	52	1	19.96 (1.33)	Self‐compassion intervention for students	Time management	SCSa	PANAS‐PA; SWLS	No follow‐ups
Sommers‐Spijkerman et al., 2018	Netherlands	245	1	52.87 (9.99)	Compassion‐focused therapy	WL	SCSa	MHC‐SF; PANAS‐PA	3 and 9 months
Susman et al., 2024	USA	140	1	20.99 (2.78)	Self‐compassionate touch	Finger‐tapping	SOCS‐S	PANAS‐PA	No follow‐ups
Villalón et al., 2023	Chile	120	1	No data	Mindfulness‐based inter‐care intervention	G1. Psychoeducational intervention G2. TAU	SCSa	MHC‐SF	3 months
Wong & Mak, 2016	China	112	1	20.50 (1.43)	Self‐compassion writing	Control writing	SCSa	PANAS‐PA	3 months
Zeng et al., 2019	China	101	1	27.55 (10.11)	Heart of joy to cultivate appreciative joy	WL	AJS	SWLS	1 month
Ziemer et al., 2019	USA	152	1	19.00 (0.22)	Self‐compassion writing	Narrative writing	SCSa	PANAS‐PA	No follow‐ups
LEADERSHIP
Schwatka et al., 2022	USA	250	1	41.7 (11.9)	Worker health leadership development programme	WL	HWAR	Staehr et al.’s 5‐item scale	No follow‐ups
Unsworth & Mason, 2012 (Study 1)	Australia	71	1	45.72 (ND)	Self‐leadership training	WL	Revised Self‐Leadership Questionnaire	Job Affect Scale	No follow‐ups
LOVE
Antoine et al., 2020	France	98	1	38.65 (12.9)	Positive psychology intervention for couples	WL	DAS	SWLS	1 month
Coulter & Malouff, 2013	USA	202	1	35.00 (11.22)	Online positive‐psychology intervention	WL	RASb	PANAS‐PA	4 months
Couper et al., 2015	Australia	124	2	62.75 (5.90)	Cognitive existential couple therapy	TAU	FRI	MHI‐38‐Well‐being	9 months
Hilpert et al., 2016	USA	440	1	39.95 (8.85)	Self‐directed couple coping enhancement programme	WL	MCQ; RAS	SHSa; SWLS	3 and 6 months
Manne et al., 2011	USA	142	2	57.85 (8.4)	Intimacy‐enhancing therapy	TAU	DAS	MHI‐38‐Well‐being	No follow‐ups
Manne et al., 2016	USA	604	2	55.70 (10.88)	Couple‐focused group intervention	Couple's support group	DAS	MHI‐38‐Well‐being	6 months and 1 year
Miller et al., 2013	USA	94	2	51.76 (15.23)	Motivational therapeutic assessment	Psychoeducation about the control theory of pain	DAS	PES questionnaire	1 month
O'Connell et al., 2016	Ireland	225	1	34.17 (12.36)	Positive psychology activities	Three things that occurred over the day	Relationship satisfaction 5‐point Likert scale	SHSa	6 weeks
Schaer et al., 2008	Switzerland	314	1	40.03 (7.77)	Couples coping enhancement training	WL	DCI; MCQ	QAWB	5 months
PERSPECTIVE
Adair et al., 2018	USA	94	1	40.09 (13.07)	Mindfulness meditation	Health promotion	TMS‐Decentering	mDES	No follow‐ups
Ahmad et al., 2020	Canada	119	1	24.80 (6.50)	G1. Full web‐based mindfulness virtual community G2. Partial web‐based mindfulness virtual community	WL	FFMQ‐SF‐Non reactivity	BMSLSS‐PTPB	No follow‐ups
de Vibe et al., 2013	Norway	288	1	23.80 (5.20)	Mindfulness‐based stress reduction	Non‐active	FFMQ‐Non‐reactivity	SWB‐4	No follow‐ups
Gayner et al., 2012	Canada	117	2	44.20 (6.90)	Mindfulness‐based stress reduction	TAU	TMS‐Decentering	PANAS‐PA	6 months
Hanley et al., 2021	USA	288	1	24.00 (5.19)	Mindfulness‐based stress reduction	Non‐active	FFMQ‐Non‐reactivity	NSSW	2, 4 and 6 years
Josefsson et al., 2014	Sweden	126	1	48.13 (9.83)	Mindfulness meditation programme	G1. Relaxation exercises G2. WL	EQ‐Decentering	PWS	No follow‐ups
Juul et al., 2020	Denmark	71	2	ND	Mindfulness‐based stress reduction programme	G1. Locally developed stress reduction intervention G2. WT	EQ‐Decentering	WHO‐5	No follow‐ups
Lever Taylor et al., 2014	UK	79	1	28.61 (9.16)	Mindfulness‐based cognitive therapy‐self‐help	WL	FFMQ‐Non reactivity	SWLS	No follow‐ups
Lönnberg et al., 2020	Sweden	193	1	32.00 (4.00)	Mindfulness‐based childbirth and parenting programme	Lamaze childbirth class	FFMQ‐Non‐reactivity	PSOM	No follow‐ups
Maddock et al., 2019	Ireland	101	2	44.10 (16.66)	Mindfulness‐based cognitive therapy	TAU	EQ‐Decentering	PWS	3 months
Mak et al., 2015	China	321	1	22.80 (6.50)	G1. Basic mindfulness program G2. HAPA‐enhanced mindfulness program	WL	FFMQ‐Non‐reactivity	WHO‐5	3 months
Nadler et al., 2020	USA	204	1	ND	Online workplace‐based mindfulness training	WL	FFMQ‐Non‐reactivity	PANAS‐PA	No follow‐ups
Nasser & Przeworski, 2017	USA	108	1	19.13 (1.15)	Mindfulness meditation	Present moment joy	TMS‐Decentering	PANAS‐PA	No follow‐ups
Noone & Hogan, 2018	Ireland	91	1	20.92 (4.39)	Mindfulness intervention by Headspace app	Breathing exercises	FFMQ‐Non‐reactivity	PANAS‐PA; WEMWBS	No follow‐ups
Perez‐Blasco et al., 2013	Spain	26	1	34.33 (4.72)	Mindfulness‐based intervention	Non‐active	FFMQ‐Non‐reactivity	SHSa; SWLS	No follow‐ups
Pizarro‐Ruiz et al., 2021	Spain	164	1	22.06 (6.00)	Mindfulness‐based intervention	Mind training application	FFMQ‐Non‐reactivity	SWLS; PANAS‐PA	No follow‐ups
Raja‐Khan et al., 2017	USA	86	2	44.50 (12.50)	Mindfulness‐based stress reduction programme	Health education	TMS‐Decentering	PANAS‐PA	16 weeks
Uriel‐Maoz et al., 2023	Israel	109	1	39.74 (6.40)	Mindfulness‐based intervention	G1. Relaxing music G2. Non‐active	EQ‐Decentering	SWLS; PANAS‐PA	No follow‐ups
Wang & Farb, 2023	Canada	233	1	18.50 (1.47)	G1. Mindfulness meditation condition G2. Mindfulness meditation condition with choice	Stress mindset intervention	EQ‐Decentering	PANAS‐PA	No follow‐ups
Wang et al., 2023	Canada	155	1	19.00 (ND)	G1. Stress mindset intervention G2. Mindfulness with choice intervention G3. Combination of stress mindset and mindfulness interventions	Writing cause of stress and playing tetris	FFMQ‐15‐Non‐reactivity; MPoD‐t	PANAS‐PA	No follow‐ups
SELF‐REGULATION
LeBlanc et al., 2017 (Study 2)	UK	75	1	36.68 (14.90)	Emotion regulation training programme	Non‐active	ERQ‐Reappraisal; ERQ‐Supression	PANAS‐PA; SWLS	1 year
Malighetti et al., 2022	Italy	42	1	23.80 (1.58)	Virtual reality emotion regulation intervention	WL	ERQ‐Reappraisal; ERQ‐Supression	MHC	No follow‐ups
Mrazek et al., 2021	USA	41	1	20.98 (2.14)	Multifaceted intervention (lectures, discussions, and activities pertinent to self‐regulation)	WL	ERQ‐Reappraisal; SCSb	PANAS‐PA; SWLS	6 weeks
Nazari et al., 2020	Iran	70	2, 3	35.30 (3.01)	CBT transdiagnostic emotion‐focused skill‐based therapy	TAU	DERS	PANAS‐PA	No follow‐ups
Ranney et al., 2017	USA	313	1	37.03 (12.23)	G1. Reappraisal intervention (self‐distancing) G2. Reappraisal intervention (temporal distancing) G3. Reappraisal intervention (positive Reframing)	Non‐active	ERQ‐Reappraisal; ERQ‐Supression	PANAS‐PA; SWLS	No follow‐ups
Ulusoy et al., 2024	Turkey	32	3	29.26 (ND)	Dialectical behavior therapy skills training	WL/TAU	DERS	SWLS	No follow‐ups
Yamasaki et al., 2010	Japan	64	1	22.42 (3.78)	Report the most stressful event + Finding positive meaning	Active non‐specific	GCQ‐Cognitive reinterpretation; GCQ‐Problem solving	PANAS‐PA	No follow‐ups
SOCIAL INTELLIGENCE
Au et al., 2020	China	78	1	51.30 (5.86)	Connecting through caregiving	Basic skill building	A composite score of perspective taking	SWLS	No follow‐ups
Cella et al., 2023	UK	48	3	41.40	Group training for social skills in psychosis	TAU	The hinting task	PANAS‐PA	No follow‐ups
Koenig Kellas et al., 2015	USA	98	1	20.80 (3.09)	Telling/listening to a story of difficulty	G1. Telling/listening to the events of the teller's day G2. Write about more innocuous topics	OCPTS	SWLS; PANAS‐PA	No follow‐ups
SPIRITUALITY
Afrasiabifar et al., 2021	Iran	80	2	18.10 (52.90)	Spiritual intervention protocol	TAU	SWBS‐Spiritual	SWBS‐Existential dimension	No follow‐ups
Djuric et al., 2009	USA	31	2	54.20 (ND)	Dietitian counseling + Spirituality counseling	Dietitian counseling	FACIT‐Sp‐Faith	FACIT‐Sp‐Meaning	No follow‐ups
Gibbel, 2010	USA	65	3	ND	Spiritually integrated intervention	G1. Secular CBT program G2. WT	FACIT‐Sp‐Faith	FACIT‐Sp‐Meaning; PANAS‐PA	1 month
Gibbel et al., 2019	USA	40	3	42.80 (ND)	Spiritual struggles intervention	TAU	GII‐Acceptance; GII‐Presence; RCOPE‐Negative; Brief‐RCOPE‐Positive	PANAS‐PA	No follow‐ups
Jafari et al., 2013	Iran	65	2	48.00 (10.38)	Spiritual therapy	Standard management and treatment, and routine educational program	FACIT‐Sp‐Faith	FACIT‐Sp‐Meaning	No follow‐ups
McCarthy et al., 2015	USA	20	1	69.95 (8.50)	Psychoeducation about spirituality	Alternative activity	STS	LSITA‐SF	No follow‐ups
Mehdipoorkorani et al., 2019	Iran	65	1	9.29 (8.04)	Spiritual care	Training program on principles of cancer care	SWBS‐Spiritual	SWBS‐Existential	No follow‐ups
Moeini et al., 2012	Iran	64	2	60.61 (12.80)	Spiritual care	Non‐active	SWBS‐Spiritual	SWBS‐Existential	No follow‐ups
Musarezaie et al., 2015	Iran	64	2	41.62 (15.31)	Spiritual care	Non‐active	SWBS‐Spiritual	SWBS‐Existential	No follow‐ups
Sajadi et al., 2018	Iran	42	2	48.10 (12.30)	Spiritual counseling intervention	Education on nutrition, physical activity, and infection control	SWBS‐Spiritual	SWBS‐Existential	No follow‐ups
Steinhauser et al., 2017	USA	221	2	67.80 (9.20)	Outlook intervention	G1. Relaxation meditation G2. TAU	FACIT‐Sp‐Faith	FACIT‐Sp‐Meaning	7 weeks
Vermandere et al., 2016	Belgium	51	1	45.70 (ND)	Structured spiritual history taking	TAU	FACIT‐Sp‐Faith	FACIT‐Sp‐Meaning	No follow‐ups
Wu & Koo, 2016	Taiwan	103	4	73.60 (7.40)	Spiritual reminiscence intervention	Non‐active	SIW	LSSb	No follow‐ups
ZEST
Das et al., 2019	USA	240	1	46.30 (10.70)	Intervention to enhance employee health and well‐being	WL	MOS‐SF‐36‐Vitality	MOS‐SF‐36‐Emotional Well‐being; PWS‐Purpose in life	No follow‐ups
Plant et al., 2024	Netherlands	84	1	47.39 (ND)	Vitality training employee behaviour‐change techniques	WL	VTES‐Energy	VTES‐Daily life satisfaction	3 months
Schakel et al., 2020	Netherlands	69	1	22.70 (3.20)	Guided internet‐based cognitive behavioral therapy combined with a serious gaming intervention	Non‐active	Composite score of the SVS and the CIS‐20	PANAS‐PA	No follow‐ups

Note: AAA‐S = Adaptive and Aggressive Assertiveness Scales; AAS‐PA = Affect‐Adjective Scale‐Positive Affect; ABES = Appreciation of Beauty and Excellence Scale; ADES‐POS = Adapted Differential Emotions Scale‐Positive; AHI = Authentic Happiness Inventory; AJS = Appreciative Joy Scale; ASQ = Attributional Style Questionnaire; BMSLSS‐PTPB=Brief Multidimensional Students' Life Satisfaction Scale‐Peabody Treatment Progress Battery; CAT‐PA = College Adjustment Test‐Positive Affect; CEAS=Compassionate Engagement and Actions Scale; CHS = Coping Humor Scale; CIT = Comprehensive Inventory of Thriving; CLH=Compassionate Love for Humanity; CLS=Compassionate Love Scale; CS=Compassion Scale; DAS=Dyadic Adjustment Scale; DCI=Dyadic Coping Inventory; DERS=Difficulties in Emotion Regulation Scale; DFS = Decisional Forgiveness Scale; DSES=Daily Spiritual Experience Scale; ECR‐S = Experiences in Close Relationships Scale; EFS = Emotional Forgiveness Scale; EQ = Experiences Questionnaire; ERQ = Emotion Regulation Questionnaire; FACIT‐Sp = Functional Assessment of Chronic Illness Therapy‐Spiritual Well‐Being; FEX = Future Expectations Scale; FFMQ = Five Facet Mindfulness Questionnaire; FRI=Family Relationship Index; FSa = Forgiveness Scale; FSb = Flourishing Scale; FSES=Forgiveness Self‐Efficacy Scale; FS‐SH=Forbearance Scale‐Short Form; GAC = Gratitude Adjective Checklist; GCQ = General Coping Questionnaire; GII = God Image Inventory; GQ‐6 = Gratitude Questionnaire‐6; GRAT = Gratitude, Resentment and Appreciation Test; GWBS = General Well‐being Schedule; HAPA = Health Action Process Approach; HFS=Heartland Forgiveness Scale; HHI=Herth Hope Index; HM = Happiness Measures; HWAR = Healthy Workplace Assessment; ICBT = Internet‐Based Cognitive Behavioral Therapy; IHMH=Index of Happiness and Mental Health; ISS=Inventory of Social Skills; LISAT‐11 = Life Satisfaction Questionnaire‐11; LOT = Life Orientation Test; LSITA‐SF = Life Satisfaction Index for the Third Age‐Short Form; LSSa = Life Satisfaction Scale; LSSb = Life Satisfaction Scale; MCGM = Multi‐Component Gratitude Measure; MCQ = Marital Communication Questionnaire; MCS = Multidimensional Compassion Scale; mDES = Modified Differential Emotions Scale; MHC‐LF = Mental Health Continuum Scale‐Long Form; MHC‐SF = Mental Health Continuum‐Short Form; MMS‐PE = Multiple Mood Scale‐Positive Emotion; MOS‐SF‐36 = Medical Outcome Survey 36‐item Short‐Form; MPoD‐t = Metacognitive Processes of Decentering‐Trait; ND=No Data; NSSW=Norwegian Scale of Subjective Well‐being; OCPTS=Other Communicated Perspective‐Taking Scale; OHI=Oxford Happiness Inventory; OHQ = Oxford Happiness Questionnaire; OTH=Orientations to Happiness; PAL = Positive Affect List; PANAS‐PA = Positive and Negative Affect Schedule‐Positive Affect; PANAS‐X‐APA = Positive and Negative Affect Schedule‐Expanded Form‐Activated Positive Affect; PANAS‐X‐UPA = Positive and Negative Affect Schedule‐Expanded Form‐Unactivated Positive Affect; PES=Positive Emotional Style; PHI=Pemberton Happiness Index; PSOM = Positive States of Mind; PWI=Personal Well‐being Index; PWS=Psychological Well‐being Scale; QAWB = Questionnaire Assessing Well‐Being; QES = Quiet Ego Scale; QWB = Questionnaire on Well‐being; RASa = Rathus Assertiveness Schedule; RASb = Relationship Assessment Scale; RCOPE = Brief Religious Coping Inventory; RLSS = Riverside Life Satisfaction Scale; RSLQ = Revised Self‐Leadership Questionnaire; SCA = Self‐Compassionate Attitude; SCBCS=Santa Clara Brief Compassion Scale; SCF=Scale of Courtship Forgiveness; SCS‐34‐D=Self‐Compassion Scale‐34‐D; SCSa = Self‐Compassion Scale; SCSb = Self‐Control Scale; SCS‐SF=Self‐Compassion Scale‐Short Form; SFI=Secure Flourishing Index; SHSa = Subjective Happiness Scale; SHSb = Sense of Humor Scale; SIW=Spirituality Index of Well‐being; SOCS‐S=Sussex‐Oxford Compassion for the Self Scale; SPANE‐P=Scale of Positive and Negative Experience‐Positive; SPT = Subjective Probability Task; STS=Self‐transcendence Scale; SURF=Survey on Flourishing; SVS=Subjective Vitality Scale; SWBS=Spiritual Well‐Being Scale; SWLS=Satisfaction with Life Scale; TFS = Trait Forgiveness Scale; TGT = Three Good Things; TMMS‐24 = Trait Meta‐Mood Scale; TMS = Toronto Mindfulness Scale; TPAS = Types of Positive Affect Scale; TRIM‐18 = Transgression‐Related Interpersonal Motivations; VTES = The Vitality Training Evaluation Scale; WEMWBS=Warwick‐Edinburgh Mental Wellbeing Scale; WHO‐5 = World Health Organization 5‐item Well‐Being Index.

Regarding long‐term effects, only 48.8% (k = 79) of the studies included follow‐up measures of which 33.9% (k = 55) reported maintenance effects on either strength or well‐being, and 14.8% (k = 24) did not find any significant effect in any of the follow‐up measures. In terms of specific strengths, spirituality had the fewest number of studies including follow‐up (84%), followed by perspective (75%), gratitude (57.1%), and kindness (36.8%). However, from those that reported follow‐ups, all studies that were training the strength of perspective showed maintenance of results, followed by kindness (91.6%), love (87.5%), humor (60%), gratitude (46.6%), and hope (33.3%). In the next section, we present the results of our reviews categorized by the Peterson and Seligman's (2004) grouping of virtues.

EVIDENCE ON THE HUMANITY VIRTUE: KINDNESS, LOVE, AND SOCIAL INTELLIGENCE

• a Kindness. Regarding the virtue of humanity, kindness emerged as the most substantiated strength based on the available evidence. Our review encompassed trials on the cultivation of compassion and kindness, totaling 38 studies (23.4%) with 7,311 participants (22.1%). The leading research country was the USA (k = 10; 26.3%), followed by China (k = 4; 10.5%), and then Germany, the Netherlands, Chile, UK, and Portugal, contributing with two studies each (5.2%). The first study was published in 2013, with the majority published in the last decade. Participants had an average age of 34.4 years, with 47.8% aged between 18 and 27, and only 5.4% over 58 years old.

The interventions typically followed standardized protocols, including the Compassion‐Cultivation Training (CCT; Jazaieri et al., 2013) (Andersson et al., 2022; Brito‐Pons et al., 2018; Hansen et al., 2021; Rojas et al., 2023), the Compassion‐Focused Therapy (CFT; Gilbert, 2009) (Kirby et al., 2023; Sommers‐Spijkerman et al., 2018), the Compassionate Mind Training (CMT; Irons & Heriot‐Maitland, 2021) (Guo et al., 2024; Kariyawasam et al., 2023; Leboeuf et al., 2022; Matos et al., 2017, 2022), and the Loving‐Kindness Meditation (LKM; Bolognino et al., 2023; Kropp & Sedlmeier, 2019; Shahar et al., 2015). Most of these interventions combined various strategies, including meditation, with only three studies excluding meditation‐based approaches. In addition to meditation, studies incorporated psychoeducation, imagination practices, narrative exercises, or psychotherapy.

Regarding mode of delivery, 20 studies (52.6%) utilized an online format, with group‐based formats being the most common (k = 24 studies, 63.1%). The intensity of the interventions varied, with the number of sessions ranging from one to ten, often including daily meditation practices or various exercises throughout the training. The interval between sessions typically spanned one week, with total training durations ranging from one week to three months. Most of the studies focused on non‐clinical populations, with only seven studies (18.4%) involving participants with medical or psychological conditions, like emotional disorders (Al‐Refae et al., 2021), clinical psychiatric rehabilitation (Gaiswinkler et al., 2020), anxiety disorders (Guo et al., 2024), post‐traumatic stress disorder (Lang et al., 2019; Müller‐Engelmann et al., 2024), or breast cancer survivors (Haydon et al., 2023; Mifsud et al., 2021). Half of the studies included an active control group involving narrative exercises, physical activity, or other contemplative practices.

The Self‐Compassion Scale (SCS; Neff, 2003) was the most commonly used questionnaire to assess virtues, with few studies including measures of compassion toward others (Bolognino et al., 2023; Brito‐Pons et al., 2018; Hansen et al., 2021; Kariyawasam et al., 2023; Kirby et al., 2023; Krieger et al., 2019; Matos et al., 2017, 2022). Many studies included only hedonic well‐being measures such as the PANAS (Watson et al., 1988), the SWLS (Diener et al., 1985), or the Subjective Happiness Scale (SHS; Lyubomirsky & Lepper, 1999), with only four studies including eudaimonic measures, such as the Psychological Well‐being Scale (PWS; Ryff, 1989) and the Pemberton Happiness Inventory (PHI; Hervás & Vázquez, 2013) (Al‐Refae et al., 2021; Leboeuf et al., 2022; Rojas et al., 2023). Additionally, 73.1% of the studies included follow‐ups, from two weeks (Kariyawasam et al., 2023) to one year (Neff & Germer, 2013).

In terms of efficacy, 81.5% were effective in enhancing the corresponding strength, and 50% of the studies were effective in increasing well‐being. Notably, 89.4% of the studies were effective in increasing both strength and well‐being. Follow‐up results confirmed that the effects (when reported) on strength and well‐being were generally maintained (91.6%).

• b Love. A total of nine studies (5.5%) with 2,243 (6.7%) participants were found for this strength. The USA contributed the most, with five studies (55.5%). The first study was published in 2008, participants had an average age of 46.2, and the interventions typically included couple therapy or couple activities, ranging from motivational interventions (Miller et al., 2013) to intimacy couple therapy (Manne et al., 2011) and positive psychology exercises (Antoine et al., 2020; O'Connell et al., 2016). In terms of delivery mode, the majority of the studies used face‐to‐face formats (k = 7). The intensity of the interventions varied, with the number of sessions ranging from one to eight, typically spaced one week apart. Half of the studies focused on clinical populations. (k = 4).

The most commonly used questionnaire to assess love was the Dyadic Adjustment Scale (DAS; Spanier, 1976). All the studies included measures of hedonic well‐being, while none assessed eudaimonic measures. 77.7% were effective in improving the strength, and 77.7% of the studies reported significant benefits in well‐being. From those that were effective in increasing well‐being, 85.7% were also effective in increasing the strength of kindness. Nearly all the studies incorporated follow‐up periods, spanning from one month to one year. The results suggested that the effects on both the strength and well‐being were moderately maintained (87.5%).

• c Social intelligence. This strength was represented by only three studies (1.8%), which included a total sample of 224 participants (0.73%) with an average age of 37.8 years. The studies were conducted in the UK, China and the USA. The interventions involved group training for social skills (Cella et al., 2023), caregiving (Au et al., 2020), and a telling/listening to a story of struggling (Koenig Kellas et al., 2015). Remarkably, only one of these studies involved a clinical sample, specifically individuals with psychosis. All interventions were delivered face‐to‐face. The questionnaires used were specifically designed to measure social perspective‐taking, and all the studies assessed hedonic well‐being, not eudaimonic well‐being. Regarding efficacy all studies included active control conditions. Only one study significantly increased social intelligence, one study was effective in both well‐being and the strength, and another increased only well‐being. Additionally, none of the studies included follow‐up assessments.

EVIDENCE ON THE COURAGE VIRTUE: ZEST AND BRAVERY

Within this virtue, only two character strengths were included: zest and bravery, without any studies included for honesty and perseverance.

1. Zest. This strength was represented by three studies (1.8%), which totaled 393 participants (1.2%). The search encompassed studies aimed at increasing vitality, energy, or zest. The average age of the participants was 38.8 years, and the studies were conducted in the Netherlands and the USA, all in the general population. The interventions included a guided internet cognitive‐behavioral therapy (iCBT) combined with a serious gaming component (Schakel et al., 2020), a program designed to enhance employee health and well‐being (Das et al., 2019), and vitality training on behavior‐change techniques for employees (Plant et al., 2024). Only one study measured eudaimonic well‐being (Das et al., 2019). Two studies reported benefits in zest and well‐being, and one study did not report benefits in any measure. No study reported follow‐up data.

2. Bravery. This strength was represented by only two studies (k = 2; 1.2%), which included a sample of 235 participants from Brazil and Sweden, with an average participant age of 30.8 years. The search for bravery included dimensions like assertiveness or fearlessness. The interventions consisted of psychoeducation on interpersonal rights and assertive skills aimed at enhancing subjective well‐being (de Sousa & da Costa Padovani, 2021), and the Michel's (2008) “Assert Yourself” protocol (Hagberg et al., 2023). Regarding efficacy, one study did not find any significant effect, while the other study reported a significant effect on bravery but not on well‐being. Both studies included follow‐up assessments, finding significant effects on strength and well‐being.

EVIDENCE ON THE WISDOM VIRTUE: PERSPECTIVE

Within the wisdom virtue, only perspective was included, as we did not find studies on creativity, curiosity, love of learning, or judgment that met our inclusion criteria. We analyzed a total of 20 studies (12.3%), including studies designed to increase metacognition, decentering, or non‐reactivity, with 2,973 participants (9%) with an average age of 30.6 years. The USA had the highest number of studies (k = 5), followed by Canada (k = 4) and Spain, Ireland and Sweden (k = 2 each one). Most interventions were delivered face‐to‐face (k = 11).

The interventions primarily consisted of mindfulness protocols including, among others, Mindfulness‐Based Stress Reduction (MBSR; Kabat‐Zinn, 1982) (de Vibe et al., 2013; Gayner et al., 2012; Hanley et al., 2021; Juul et al., 2020; Raja‐Khan et al., 2017), Mindfulness‐Based Cognitive Therapy (MBCT; Segal et al., 2012) (Lever Taylor et al., 2014; Maddock et al., 2019). Only 4 studies (20%) were developed in clinical samples, like health care settings (Juul et al., 2020), HIV (Gayner et al., 2012), psoriasis (Maddock et al., 2019), and women with overweight or obesity (Raja‐Khan et al., 2017). Sessions were mainly conducted on a weekly basis over two months, including daily practices. All interventions incorporated meditation techniques focusing on meta‐awareness and observation of thoughts, with most also providing psychoeducation.

The questionnaires utilized to measure perspective predominantly included the decentering factor of the Toronto Mindfulness Scale (TMS; Lau et al., 2006), the non‐reactivity factor from the Five Facets on Mindfulness Questionnaire (FFMQ; Baer et al., 2006) or the Experience Questionnaire (EQ; Fresco et al., 2007), all of which have good psychometric properties. Regarding well‐being measures, most studies employed hedonic measures, with only two using an eudaemonic measure (i.e., PWS; Ryff & Keyes, 1995). 65% of the interventions were effective in increasing well‐being, and 80% in enhancing strength. Among the studies that reported positive effects on well‐being, 92.3% were also effective in increasing perspective. Additionally, 80% of the studies did not report follow‐up data, and for those that did, the results were generally maintained over time.

EVIDENCE ON THE TRANSCENDENCE VIRTUE: HOPE, HUMOR, GRATITUDE, APPRECIATION OF BEAUTY AND EXCELLENCE, AND SPIRITUALITY

All the character strengths related to Transcendence ‐hope, humor, gratitude, appreciation of beauty and excellence, and spirituality‐ were included in our analysis.

1. Hope. For this strength, the search also included the concept of optimism. A total of 15 studies (9.2%) with 2,060 participants (6.2%) were included with an average age of 34.3. The countries with the most studies were Spain (k = 4) and the Netherlands (k = 3). The first study dates back to 2011 (Meevissen et al., 2011). The interventions typically utilized the Best‐Possible‐Self (BPS) training, which includes narrative and imagination exercises. This training requires envisioning a future where all aspects have turned out in the best possible way, allowing individuals to explore their hopes, goals, and aspirations in a positive and organized manner. Half of the studies were delivered face‐to‐face (k = 8). The intensity of the interventions ranged from just instructions for writing exercises to a maximum of 12 sessions. Most interventions were single‐session, with participants asked to read and visualize the exercise over the following weeks as homework.

Regarding the sample characteristics, few studies were conducted with clinical populations (k = 4), including individuals with eating disorders (Enrique, Bretón‐López, Molinari, Roca, et al., 2018), heart disease (Mohammadi et al., 2018), fibromyalgia (Molinari et al., 2018) and Parkinson's disease (Murdoch et al., 2020). The most used questionnaire to assess this virtue was the Life Orientation Test (LOT; (Scheier & Carver, 1985). All studies included only hedonic well‐being measures, predominantly the PANAS. Follow‐up measures were reported in 80% of studies, with a range from one week (Dennis & Ogden, 2022; Heekerens et al., 2020; Peters et al., 2013) to four months (Mohammadi et al., 2018). In terms of efficacy, 53.3% (k = 8) of the studies reported a significant increase in well‐being, only 33.3% (k = 5) increased hope and 40% (k = 5) were not effective at all. Of those that were effective in increasing well‐being, 50% were also effective in increasing the strength of hope. In the follow‐ups, eight studies found no sustained positive effects, and only four reported positive effects on hope.

• b Humor. A total of seven studies (4.3%) were included, with 3,286 participants (9.9%), with an average age of 46.5 years. The interventions typically included the three playful or funny things exercise, which aims to increase awareness of humorous moments, or humor‐based training. These interventions combined various strategies such as psychoeducation, narrative exercises, imagination activities and awareness of daily humorous situations.

In terms of delivery format, four were conducted face‐to‐face and in individual settings. The number of sessions ranged from one to ten, often including daily meditation practice or various exercises throughout the training period. The interval between sessions was typically one week, although many interventions focused on daily practice. The total training duration ranged from two days to two months. Regarding participant characteristics, three studies involved clinical populations, including individuals on hemodialysis (De Sousa et al., 2019), in palliative care (Linge‐Dahl et al., 2023), and with emotional disorders (Tagalidou, Distlberger, et al., 2019). Five studies included an active control group with narrative exercises or other positive psychology techniques as the comparison condition. The most commonly used questionnaire to assess humor was the State–Trait‐Cheerfulness Inventory (STCI; Ruch et al., 1996), although other measures such as the Sense of Humour Scale (SHS; Ruch & Heintz, 2018) were also used. For well‐being outcomes, three studies measured eudaimonic well‐being using the Authentic Happiness Inventory (AHI; Shepherd et al., 2015).

In terms of efficacy, more than half of the studies were effective (57.1%) in increasing both humor and well‐being. All the studies that reported significant enhancement of well‐being also reported an increase in humor. Additionally, of those studies that reported follow‐up measures (71%), 60% found that the results were maintained.

• c Gratitude. The literature on gratitude is extensive and well‐established, highlighting the centrality of this strength (Diez et al., 2023). A total of 35 studies (21.6% of the total included in our review) with 7,000 participants were examined (21.1% of the entire sample). The USA contributed the most studies (k = 17, 48.5%), followed by China (k = 5, 14.2%). The earliest study dates back to 2003 (Emmons & McCullough, 2003). The average age of participants across studies was 32 years.

The interventions aimed at cultivating gratitude typically included exercises like the three good things intervention (Gold et al., 2023; Krentzman et al., 2015; Li et al., 2021; Linley et al., 2013; Srivastava & Ghosh, 2023) or gratitude diaries. Most of the studies were delivered online (k = 20). In terms of intensity, the interventions varied widely, with exercises performed daily over periods ranging from four days to three months. These exercises often required minimal professional involvement, often being self‐guided daily practices.

The most frequently used questionnaire was the Gratitude Questionnaire‐6 (GQ‐6; McCullough et al., 2002). Well‐being was primarily assessed with hedonic measures like the PANAS (Watson et al., 1988) and the SWLS (Diener et al., 1985). Most studies were conducted with non‐clinical samples. Seven studies were conducted with clinical populations, addressing conditions like cancer (Adelstein, 2016), chronic pain (Condon, 2022), congenital or adult‐onset neuromuscular diseases (Emmons & McCullough, 2003), emotional disorders (Kerr et al., 2015), alcohol use disorder (Krentzman et al., 2015) and risk of suicide and depression (Hames, 2015). In terms of efficacy, 61% of the studies reported significant improvements in wellbeing, and 60% increased gratitude. Only a minority of studies (20%) included clinical samples (Adelstein, 2016; Bohlmeijer et al., 2021; Condon, 2022; Emmons & McCullough, 2003; Kerr et al., 2015; Li et al., 2021). All of these clinical studies, except Li et al. (2021), showed positive effects in both gratitude and well‐being. Moreover, 90.4% of the studies that improved well‐being also showed a positive result in gratitude. Only 15 studies reported follow‐ups with only four showing maintained gains in both gratitude and well‐being. Two studies reported sustained positive effects in gratitude but not well‐being. This suggests that although gratitude interventions can have an impact in the short‐term, the long‐term maintenance of benefits may be more variable and require further research attention.

• d Appreciation of beauty and excellence. Regarding the appreciation of beauty and excellence, only one study was included, conducted by Martínez‐Martí et al. (2018) in Spain. This study involved a sample of 204 participants (0.6% of the total sample) that underwent an intervention aimed at cultivating positive attitudes toward their social or physical environment. The researchers developed a specific measure called the Appreciation of Beauty and Excellence Scale (Martínez‐Martí et al., 2018) to assess the outcomes. The intervention encompassed various techniques, including journaling, awareness exercises, and psychoeducation. Although the study did not find significant impacts on increasing appreciation, it was effective in enhancing well‐being.
• e Spirituality. A total of 13 studies (8%) were included, encompassing 911 participants (2.7% of the total sample), with an average age of 48.3 years. Iran had the highest number of studies (k = 6), followed by the USA (k = 5). This is the only area of studies in which a non‐western country leads the research. The interventions typically included spirituality care or counseling, with the majority conducted in clinical samples (k = 10, representing 76.9% of the total number of participants), covering areas such as hematology oncology, heart failure, pulmonary, and nephrology (Steinhauser et al., 2017), breast cancer survivors (Djuric et al., 2009), cancer (Afrasiabifar et al., 2021; Jafari et al., 2013; Sajadi et al., 2018), mental disorders (Gibbel, 2010; Gibbel et al., 2019), leukemia (Musarezaie et al., 2015), dementia (Wu & Koo, 2016), palliative care (Vermandere et al., 2016), and cardiac ischemia (Moeini et al., 2012).

Regarding measures of outcomes, several studies utilized the same scale to assess both spirituality and eudaimonic or existential well‐being, like the Spiritual Well‐being Scale (SWS; Ellison & Smith, 1991). However, some authors indicate that the religious dimension should not be conflated with spirituality, but rather considered as an outcome variable. Thus, for our purposes, it is used as a mechanism (Paloutzian et al., 2021) for the existential dimension (more related to psychological well‐being). Another commonly used measure was the Functional Assessment of Chronic Illness Therapy—Spiritual Well‐Being (FACIT‐SP; Peterman et al., 2002), which also has two factors, the first assessing a sense of meaning and peace, while the second evaluates the role of faith in the context of illness.

In terms of the delivery mode, only three studies were conducted online. The interventions had a diverse format, with the number of sessions ranging from three to twelve, typically spaced weekly, and durations varying from three days to four months. Ten studies (76.9%) reported efficacy in increasing well‐being, while only six studies (46.1%) significantly increased spirituality. Notably, 60% of the studies that were effective in increasing well‐being also showed positive effects on spirituality. Only two studies reported data about follow‐up, with only one reporting sustained improvements in spirituality.

EVIDENCE ON THE TEMPERANCE VIRTUE: FORGIVENESS, HUMILITY, SELF‐REGULATION, AND LEADERSHIP

1. Forgiveness. With a total of five studies (3%) and 5,069 participants (15.3%) with an average age of 25.7 years, this was one of the strengths with the largest sample size. The USA contributed the most studies, and the one with the largest sample was multinational (Ho et al., 2024, n = 4,786). The interventions were primarily based on established models such as the REACH forgiveness program (McCullough et al., 2000) and Enright's model (Enright, 2012). These interventions typically included components like psychoeducation, guided imagery, role playing or behavioral techniques.

The scales used to measure forgiveness were the TRIM‐18 (McCullough et al., 2006) and the Decisional and Emotional Forgiveness Scale (Worthington et al., 2007). Notably, only one study was conducted online (Ho et al., 2024). Of all studies, three reported increases in both well‐being and forgiveness, while one showed benefits in well‐being alone, and another showed an increase in well‐being but not in forgiveness. It is worth mentioning that 75% of the studies reporting positive results in well‐being also indicated a positive effect on forgiveness. However, most studies were primarily compared against passive controls, and only three provided follow‐up data, which revealed varied effects.

• b Humility. Only two studies were included (1.2%) with a total of 107 participants (0.3%), both conducted in the USA, with a non‐clinical sample, and an average age of 28 years. The studies used a “quiet ego” intervention (Liu et al., 2022; Wayment, Collier, et al., 2015), and the “Quiet ego” scale (Wayment, Bauer, & Sylaska, 2015) to measure the strength. The interventions featured audio‐recordings with psychoeducation and narrative exercises. Both studies were effective in increasing humility and well‐being compared to active and passive controls, though neither reported follow‐up data.
• c Self‐regulation. In the domain of self‐regulation, a total of seven studies (4.3%) were included, comprising a total of 637 participants (1.9%) with an average age of 29.3 years. The interventions primarily focused on emotion regulation, including Cognitive Behavioral Therapy (CBT) (Nazari et al., 2020), Dialectic‐Behavioral Therapy (DBT, Ulusoy et al., 2024), and reappraisal techniques (Ranney et al., 2017). The most commonly used measure of the strength was the Emotion Regulation Questionnaire (ERQ; Gross & John, 2003), while well‐being was measured only with the hedonic component by typically using the PANAS (Watson et al., 1988) and the SWLS (Diener et al., 1985). Two studies specifically targeted mental disorders (Nazari et al., 2020; Ulusoy et al., 2024). Five studies reported effectiveness in increasing well‐being (71.4%), and five (71.4%) in increasing the strength. Notably, 80% of the studies that were effective in enhancing well‐being, were also effective in increasing the self‐regulation strength. Only one study reported follow‐up data, which indicated maintenance of self‐regulation improvements.
• d Leadership. This was the sole strength analyzed within the virtue of Justice, as fairness was merged with kindness, and no studies on teamwork met the criteria to be included in the systematic review. Only two studies were included (1.2%) with 321 participants (0.9%) and an average age of 43.7 years. The interventions focused on a worker health leadership development program, conducted with employee samples, comparing the outcomes with a waiting list and not including follow‐up measures. The age average was 43.6 years, and the studies were conducted in the USA (Schwatka et al., 2022) and Australia (Unsworth & Mason, 2012). In terms of efficacy, one study (Unsworth & Mason, 2012) reported effectiveness in enhancing both leadership and well‐being, while Schwatka et al. (2022) reported benefits in well‐being alone without having a significant impact on leadership.

Risk of bias

Risk of bias summaries and ratings for each study are presented in the Supplementary material. Studies were classified as high, some concerns, or low risk of bias. A total of 71.6% of the studies reported a high risk of bias, primarily due to the lack of adherence assessment (domain 2; 60.4%) and inadequate missing data handling (domain 3; 53%). Additionally, 27.1% showed limitations due to insufficient information on analytical plans in the pre‐registration (some concerns). Only two studies (1.2%) were rated as having a low risk of bias according to our criteria. The strengths which showed the lowest risk of bias were love (55.5% of the studies presented some concerns), perspective (40% of the studies presented some concerns and 5% low risk), hope (40% of the studies with some concerns), humor (28.5% of the studies presented some concerns), kindness (21% of the studies presented some concerns and 2.6% low risk), and gratitude (22.8% of the studies presented some concerns). The strengths that showed the highest level of risk were self‐regulation, leadership, appreciation of beauty and excellence, zest, and spirituality (with 92.3%).

DISCUSSION

The objective of this series of systematic reviews was to provide a comprehensive overview, for the first time, of the evidence on the efficacy of RCTs aimed at increasing character strengths and measuring well‐being. To achieve this objective, a total of 61,479 abstracts were reviewed, and 162 studies with 32,309 participants were included. Only 21 systematic reviews were conducted (after merging some strengths due to overlap between constructs and lack of research in certain areas). In total, 17 strengths had a sufficient number of studies that met the inclusion criteria. The strengths of curiosity and love of learning, perseverance, honesty, judgment, and prudence, had no studies that met the inclusion criteria.

Over two‐thirds of the studies reported significant improvements in the specific strengths targeted by the intervention, with 64.3% indicating efficacy compared to active controls and 69.3% compared to passive controls. Training in kindness (mainly self‐compassion), love, and perspective (mainly mindfulness‐based interventions) showed the best results in modifying these strengths, with over 80% of studies showing positive results when compared to passive controls. Interestingly, interventions aimed at increasing hope were less effective, with only about 30% of studies successfully enhancing this strength. Most hope‐related studies employed the “best possible self” intervention and used the LOT (Scheier & Carver, 1985) as the main questionnaire. The lack of positive results may be attributed to the questionnaire's poor ability to measure the strength (or to the limited impact of the intervention strategy). The factor structure of the LOT has shown inconsistencies (Long et al., 2020), potentially biasing the underestimation of the effects of the interventions (Malouff & Schutte, 2017). Furthermore, research has shown that optimism, rather than being a trait, exhibits state‐like, dynamic, situation‐specific qualities (Hoeppner et al., 2021) that encompass cognitive and emotional facets that are differentially associated with well‐being (Pleeging et al., 2021). Although “best possible self” short interventions have been shown to enhance positive affect, their capacity to increase optimism or hope remains unclear. This contrasts with prior literature, where a meta‐analysis reported significant increases in optimism (Carrillo et al., 2019), indicating a need for further research to clarify this discrepancy. In 2021, McGrath (2021) stated that “Virtue acquisition can be fostered by well‐designed, structured interventions.’ Is this true for all virtues?”. Our analysis suggests that not all strengths are equally trainable or equally effective in increasing well‐being, with interventions fostering perspective, love, spirituality, forgiveness, and gratitude showing the best results. However, this should be interpreted with caution, as not all strengths are supported by the same level of evidence or study quality. For instance, many studies of spirituality present a risk of bias, while studies on love and forgiveness are few (nine and five, respectively). The five strengths with the best percentage of studies showing efficacy and also the lowest risk of bias were kindness, perspective, humor, hope, and gratitude.

Despite the limited research on some strengths, our results suggest that the overall evidence is mixed and varies depending on the comparators and the studied strengths, with more than half of the studies showing positive outcomes related to well‐being. Of the reviewed studies, 61.7% demonstrated effectiveness in enhancing well‐being, with 52.5% of the interventions being significantly more effective than active control groups and 76.1% more effective than passive control groups. The highest percentage of studies showing success in increasing well‐being compared to passive controls was observed in the strengths of perspective, love, spirituality, forgiveness, and gratitude. In studies comparing the intervention with active controls, the studies showing more improvements were humor and spirituality. Other strengths, such as zest and social intelligence, also showed promising results, but the small number of studies precludes drawing firm conclusions.

The fact that almost half of the studies did not report any effect on well‐being raises important questions about the variability in the effectiveness of these interventions. This variability may be due to certain strengths being more trainable than others, or some strengths leading to increased well‐being while others do not. Other critical factors to consider include differences in study design (e.g., statistical power, risk of bias, or measurement of outcome and strengths), intervention characteristics (duration of the intervention, inclusion of meditation practices, intensity of training, delivery format, or intervention fidelity), and participant characteristics (e.g., gender, age, baseline strengths and well‐being, clinical or general population, or cultural backgrounds). These findings highlight the need to refine intervention approaches, ensuring they are both well‐targeted and robust enough to yield consistent outcomes across diverse populations.

The results partially align with previous meta‐analyses about the capacity of different families of psychological interventions (e.g., CBT, positive psychology, mindfulness) to increase well‐being (Van Agteren et al., 2021; Carr et al., 2024). However, Van Agteren et al. (2021) focused more on programs than on specific techniques, and only the strengths of compassion and perspective (mindfulness) were specifically analyzed in their study. Nevertheless, our findings were consistent with theirs, particularly regarding the positive impact of mindfulness training and positive psychology interventions in a variety of participants (healthy participants and individuals with physical or psychological problems).

It is important to note that only half of the studies reported follow‐up data, and among those, 48.7% found that the effects on well‐being were maintained. Although the meta‐analytic literature of positive interventions has shown that, in general, the effects on distress and well‐being measures are maintained for several months after the intervention programs (Carr et al., 2024), our findings underscore the need for further research on the long‐term effects of strength‐based interventions. Studies including follow‐up designs also varied substantially across strengths, with 100% of studies on perspective including longitudinal observations, compared to only 33% for gratitude. This variability may be due to differences in the intensity of the interventions. Perspective, love, and kindness were tested with the longest and most intense training programs (e.g., manualized meditation‐based interventions with eight weekly sessions), whereas gratitude was typically trained with less intensive intervention.

Our main objective was to explore the efficacy of interventions aimed at enhancing psychological strengths and their associated effects in increasing well‐being. Although the intrinsic limitations of systematic reviews make it difficult to definitively answer this question, we can highlight that among the studies reporting significant increases in well‐being, most also found a significant impact on the associated strengths, particularly humor, kindness, self‐regulation, and perspective. This suggests that interventions designed to enhance strengths may also impact an individual's well‐being. However, the directionality of this association could also be in the opposite direction, as proposed by eudaimonic well‐being theories (Huta & Waterman, 2014), and furthermore, we also can not confirm that in individual level, changes in strengths are related to wellbeing outcome. From the perspective of strengths and virtues, eudaimonia has been conceptualized as the process of identifying one's unique character strengths, developing them, and using them in the service of greater goods, particularly the welfare of humankind (Peterson et al., 2005). Thus, the recognition and embodiment of strengths might be key mechanisms by which these interventions ultimately enhance well‐being. Although our results point in that direction, they also show that this relationship may not be uniform across all the strengths, including the lack of robust positive evidence for strengths like spirituality and hope.

Another important consideration when studying the possible mechanisms by which VBIs affect well‐being is that there may be other contributing factors, previously identified in the general literature of psychological interventions, such as therapeutic alliance, group cohesion, and other common factors (Wampold, 2015). In addition, demographic and cultural variations may also moderate this relationship. Most studies were conducted in Western countries, raising concerns about the applicability of findings to populations with different social structures or healthcare systems. The geographic homogeneity of the studies may exacerbate this issue, leaving important realities in other contexts unaddressed (Oishi et al., 2022). Thus, further research addressing the study of potential moderators and mechanisms of change in VBIs is essential to understand and optimize their efficacy.

The quality of the reviewed studies is predominantly problematic, with only a few meeting high‐quality standards according to the Risk of Bias tool (Higgins et al., 2011). The most problematic risks of bias are related to the absence of a pre‐registered analysis plan, a lack of appropriate adherence analysis (domain 2), and poor management of missing data (domain 3). Examples of adherence analysis include intention‐to‐treat analyses or screening and modeling differential dropout (e.g., Cella et al., 2023; Juul et al., 2020; Steinhauser et al., 2017). Adequate management of missing data involves reporting its presence and patterns, and implementing justified up‐to‐date management methods (e.g., full‐information maximum likelihood, multiple imputation, Bayesian imputation). Thus, this field requires higher quality in terms of designing the studies and the consistent use of pre‐registrations so that analysis processes and conclusions can be properly scrutinized. Some strengths stand out due to the low quality of the studies. Among strengths with a considerable number of questionable studies, spirituality and love have the highest proportion of studies with some risk of bias (92.3% and 100% respectively), while others, such as kindness or gratitude, benefit from a stronger research tradition, leading to studies of much higher quality (Gu et al., 2022).

The lack of evidence of RCT interventions for strengths such as social intelligence, humility, zest, teamwork, and leadership is particularly striking. This result is particularly significant given the widespread consensus in mainstream media (Folk & Dunn, 2024) regarding their role as sources of well‐being and flourishing. Equally notable is the scarcity of high‐quality intervention studies on spirituality. While there are sufficient studies in this domain, their quality is too limited to draw reliable conclusions. Moreover, these studies often do not include psychometrically reliable and valid measures of spirituality as a strength. Furthermore, a major challenge is that spirituality is often used in an interchangeable way with religiousness, leaving studies approaching spirituality as a universal virtue, not specifically related to religious practices and beliefs, as a minority (de Jager Meezenbroek et al., 2012; Lucchetti et al., 2021). Fortunately, some scales have emerged that may offer a promising alternative for assessing this strength in the future, such as the Spiritual Attitude and Involvement List, both in its long and short formats (SAIL and SAIL‐SF; Bohlmeijer et al., 2023; de Jager Meezenbroek et al., 2012).

There is also an absence of RCTs examining interventions on the strengths of creativity, teamwork, honesty, curiosity and love of learning, justice and prudence, and perseverance. This lack of interest in researching the impact of their training in well‐controlled ways may be due to several factors. Historically, these strengths have been under‐researched and lacked appropriate instruments for their evaluation. It is also possible that these strengths are assumed to be less modifiable, or existing studies may simply not have met the quality standards necessary to be included in the systematic reviews. (In Figure 1, the number of studies excluded for each criteria can be observed.) For example, the lack of RCT design and not measuring well‐being are the main reasons for exclusion. In any case, research into the cultivation of these strengths deserves greater attention and development.

Virtues with a robust research tradition benefit more from using well‐established instruments with good psychometric properties and from framing the studies within more complex theories about the construct. For example, strengths like kindness, forgiveness, hope, humor, perspective, and gratitude are assessed using instruments with fair to good psychometric properties, such as the FFMQ‐short form (Bohlmeijer et al., 2011; Mattes, 2019), the SCS (Muris & Otgaar, 2020; Neff, 2003), or the GQ‐6 (McCullough et al., 2002). In contrast, the absence of psychometrically solid instruments for assessing crucial strengths such as zest, curiosity, or honesty is particularly noteworthy. Although the VIA and its multiple adaptations are available to evaluate each of the proposed twenty‐four strengths (Niemiec, 2013), their limitations may lead researchers to consider other more specialized alternatives or with stronger evidence supporting their properties. Indeed, only one study in our systematic review used the VIA questionnaire to assess changes in strengths (Datu et al., 2022). One important limitation of the VIA is its considerable length, as it includes several strengths that may not be relevant to a particular intervention. Another limitation involves its debatable content regarding strengths (McGrath, 2021). More specialized instruments can be better suited to capture specific constructs more effectively and efficiently (e.g., the SCS for measuring self‐compassion).

Another relevant conclusion of our review is that, despite the theoretical framework suggesting a relationship between virtuous behaviors and a eudaimonic perspective (Huta & Waterman, 2014), the percentage of studies incorporating measures of eudaimonic well‐being is minimal. This underutilization of eudaimonic instruments may be due to several reasons. The lack of solid psychometric instruments is an unlikely reason, given that established tools like the PWBS (Ryff, 1989), the Flourishing Scale (FS, Diener et al., 2010), and the Eudaimonic Well‐Being Questionnaire (EWBQ; Waterman et al., 2010) are available, among others (Linton et al., 2016; Vázquez et al., 2023). One more plausible reason is the lack of consensus on the definition of eudaimonia (Huta, 2018). According to Huta and Waterman (2014), definitions of eudaimonia focus on distinct categories that address different aspects of a process: orientations (priorities, motives, values, goals), behaviors (specific activities), experiences (feelings, emotions), and functioning (traits, abilities, habits, character strengths). This lack of a unified definition likely affects the selection and use of eudaimonic constructs and related instruments of assessment.

Interestingly, the most widely used instrument to assess well‐being in our systematic reviews is the PANAS, a measure of hedonic well‐being that unfortunately only covers positive and negative emotions of high arousal. It is likely that many interventions aimed at improving well‐being have an impact on low‐arousal positive emotions (e.g., calmness, content) that are not covered by instruments like the PANAS (Roca et al., 2023). However, despite this customary tendency in the use of well‐being instruments, the positive impact of the interventions on eudaimonic well‐being appears more often in eudaimonic measures than in hedonic ones (70% vs 62%). Additional research must delve deeper into the complex relationship between VBIs and hedonic and eudaimonic well‐being to better understand these dynamics and to select the most sensitive tools to detect significant changes.

All the interventions reviewed in our study correspond to one or several key elements of learning proposed by Lavy (2020) in strengths interventions: a) providing theoretical knowledge or conceptualization, b) encourage recognition in oneself, c) encourage action, and d) encourage reflection on one's own or others' use of strength. However, the specific impact of these elements remains unclear. For instance, some VBIs are more oriented toward reflection (e.g., gratitude interventions), while some emphasize a systematic training (e.g., meditation‐based interventions). Furthermore, although there are interventions focused solely on providing knowledge and recognition, such as ‘signature strength’ interventions (Schutte & Malouff, 2019), with promising effects on mental health, they were not included in the present systematic review because they were not specifically designed to enhance a specific strength. The effectiveness of VBIs according to their elements, as well as other dimensions that could moderate efficacy like intensity, inclusion of meditation, duration, health conditions, gender, ethnicity, and religious beliefs remains underexplored.

A more in‐depth and comprehensive analysis is necessary to better understand the full range of impacts these interventions may have, including how they interact with various factors such as individual characteristics, environmental conditions, and other contextual variables (Miller, 2016). Such analysis would allow researchers to draw clearer conclusions about the effectiveness of VBIs and could provide crucial insights for refining and optimizing future interventions. We simply counted the number of studies with positive findings in each virtue and strength, which does not account for differences in effect sizes and study precision. Nonetheless, the present evidence mapping exercise can serve as a useful starting point for conducting such meta‐analysis.

Limitations

The present study has a number of limitations. The primary limitation is that by requiring the evaluation of trait‐like measures assessing each strength, many studies were excluded because they did not meet this criterion, as shown in Figure 1. Although this exclusion was justified by our goal of mapping the evidence of interventions on strengths and virtues that have measured well‐being, it may have hindered our ability to obtain a complete map of the field of study. Nevertheless, only 18% of the excluded studies were RCTs that targeted a strength but did not include a measure of well‐being. Therefore, it is unlikely that a representation bias from RCTs focusing on strengths without assessing well‐being would substantially affect our general conclusions. However, regarding the representativeness of studies, future research could systematically explore RCTs that examine outcomes related to negative mental health conditions, such as anxiety or depression. Conceptually, enhancing strengths may indirectly contribute to well‐being by reducing distress.

The ambitious scope of our study, which involved analyses of 21 systematic reviews, may have led to significant heterogeneity in the results. Variations in outcome measures, trial designs, sample sizes, intervention methods, and sociodemographic characteristics complicate the comparison of findings across studies. The low quality of many included studies also limits the robustness of the conclusions that can be drawn, further complicating the reliability of the review's findings.

Another potential limitation relates to the VIA model of 24 strengths and six virtues. Exploratory latent structural analyses have failed to find support for the six domains as differentiable clusters of the 24 strengths (McGrath, 2021). Although this discussion is beyond the scope of our work, it does highlight some ongoing debates in the field. A related concern with this model is that although it rightly proposes that virtues have value if embodied in actions (i.e., virtues in action), the literature on character strengths and virtues is saturated with studies in which only self‐report instruments are used to assess them. Although this is a generally growing problem in psychological research (Baumeister et al., 2007), there is a need for primary studies to take an additional step to complement the assessment of these constructs, and their changes following interventions, with behavioral measures.

The search process also presented limitations, particularly in relation to the strength of perspective. Many studies for this strength had to be incorporated manually as one of the most commonly used measures to assess it was the ‘non‐reactivity’ factor from the FFMQ questionnaire, which is not typically mentioned in article titles or abstracts. Consequently, we relied on other previous meta‐analyses (van Agteren et al., 2021) and further conducted manual searches to identify relevant literature, running the inevitable risk, despite our careful procedures, of excluding some relevant studies in the field.

Another limitation of our review is the potential presence of publication biases. Studies with positive or significant findings are more likely to be published, while those with null or negative results may be underreported. Although we included studies where no significant relationship was found between VBIs and well‐being or strengths and virtues, we cannot rule out the possibility that positive findings are overrepresented. This bias could lead to an overestimation of the efficacy of these interventions. Therefore, the findings should be interpreted with caution, and future meta‐analyses should further investigate the potential existence of this bias.

Future agenda and research

To promote significant advances in this important area of research, it is essential to improve the quality of the intervention studies in this field (Folk & Dunn, 2024). Another key recommendation is to focus on under‐researched strengths that have significant potential to impact well‐being, such as zest, leadership, curiosity, wisdom, or appreciation of beauty and excellence. Well‐designed and rigorously controlled interventions targeting these strengths could yield promising and impactful results.

In terms of assessment, we also advocate for the increased use of eudaimonic well‐being instruments as an outcome measure in virtue‐ and strength‐based interventions. Additionally, it is imperative to develop reliable psychometric instruments and behavioral indicators that are sensitive to change and supported by rigorous psychometric analyses (Moskowitz et al., 2020). Future research also needs to incorporate intervention fidelity assessment in the trials as well as other well‐known aspects of solid RCTs in the clinical field. This step aligns with a growing movement in psychological change research that emphasizes the need to delve deeper into the moderators and mechanisms of change that contribute to the success of interventions (Tolin et al., 2023). By identifying these factors, researchers will better understand how and why certain interventions work, thereby refining them for greater efficacy and ensuring they can be adapted to meet diverse needs and contexts.

CONCLUSIONS

This study is the first to synthesize the impact of VBIs on both strengths and well‐being across a broad spectrum of character strengths. The evidence of RCT studies is highly heterogeneous, making it challenging to draw definitive conclusions on this emerging field. Although cultivating some character strengths shows rather robust results, there is insufficient evidence to support the idea that cultivating virtues in general is associated with reliable improvements in well‐being. While the majority of studies report positive outcomes, the variability in results underscores the complexity involved in the ambitious and legitimate goal of enhancing well‐being and human virtues. Future research should continue to increase the quality and rigor of these interventions and develop more precise methods for evaluating their impact. This will be crucial for advancing the field and achieving the goal of improving well‐being through character development.

CONFLICT OF INTEREST STATEMENT

None of the authors have a conflict of interest to disclose.

ETHICS STATEMENT

Not applicable because of the nature of the studio (literature review).

Supporting information

Table S1: VIA model of strengths and virtues (Peterson & Seligman, 2004)

Table S2: Frequency of countries in which studies were conducted

Table S3: Inter‐rate agreement for each character strength

Table S4: Summary of risk of Bias profiles of included studies

Table S5: Outcome measures used to measure character strengths and well‐being in the included studies.

Table S6: Summary of findings per virtue.

Figure S1. Summary of findings per strength.

Cebolla, A. , Navarro‐Siurana, J. , Galante, J. , Sarrión, P. , Vidal, J. , Fernández‐Castilla, B. , Lecuona, O. , Vázquez, C. , & Baños, R. M. (2025). A synthesis of RCTs on psychological interventions fostering strengths and virtues: Evidence from 21 systematic reviews. Applied Psychology: Health and Well‐Being, 17(4), e70069. 10.1111/aphw.70069

DATA AVAILABILITY STATEMENT

The study data, codebook, and analysis code are openly available in the Open Science Framework at https://osf.io/75zdr/.