Skip to main content
. 2022 Aug 27;19(17):10706. doi: 10.3390/ijerph191710706

Table A1.

Summary of studies with prevalence and correlates of Burnout/Stress.

Authors/Year Country Study Design Sample/Population Size (Response Rate %) Teachers/Age Range Scales Used Key Findings
Correlates of Burnout/Stress Prevalence of Burnout/Stress
Okwaraji et al., 2015 [47] Nigeria Cross-sectional SS = 432 Secondary 26–48 years Maslach burnout inventory,
The General health questionnaire (GHQ-12) and the Generic job satisfaction scale
DP: gender, marital status
Reduced PA: age, gender, marital status.
40% emotional exhaustion EE
39.4% for DP
36.8% for reduced PA.
Kidger et al., 2016 [81] UK Cross-sectional 555/708/ (78.4%) Secondary Warwick Edinburgh Mental
Wellbeing Scale-WEMWBS)
Stress at work: change in school governance. Not Mentioned.
Bianchi et al., 2015 [99] France Survey SS = 627 Primary/Secondary Maslach Burnout Inventory (MBI) Burnout symptoms at time 1 (Tl) did not predict depressive symptoms at time 2 (T2). Time 1 43%, mild burnout 49% moderate burnout, 8% severe burnout.
Ramberg et al., 2021 [91] Sweden Cross-sectional Year 2014/16 3948/7147 (55.2%) SS Final = 2732 Teachers Stockholm Teacher Survey. The (Questionnaire) Perceived stress: high job strain, high SOC.
Stress: psychological demands at work. High SOC was linked with lower levels of stress and depressed mood. Variation of 4.8% for perceived stress and 2.1% for depressed mood.
Not mentioned.
Shukla et al., 2008 [7] India Survey SS = 320 Secondary Maslach Burnout Inventory Lack of PA: subject taught. Science teachers’ higher burnout than arts teachers. More burnout cases in English medium teachers than Hindi medium.
Burnout: gender.
EE: 56.56% low burnout, 19.68% average, 23.75% high.
DP: 20% high burnout, 16.56% average, and 63.43% low.
Lack of PA: 28.43% high burnout. 13.43% average, and 58.12% low.
Lack of PA: 28.43%
11.88% high burnout level in all 3 dimensions, 2.81% average burnout on all 3 sub-scales and 40% low burnout level in all dimensions.
Burnout of SCIS teachers 26.26%, (AS, 13.76%.
EE: 22.5% SCIS and 25% AS teachers’ high burnout category, 21.88% SCIS and 17.5% AS teachers’ average burnout level, 55.62% SCIS and 57.5% AS teachers’ low burnout.
Approximately 56–64% in all dimensions of the sample is showing low burnout levels.
Pohl et al., 2022 [48] Hungary Cross-sectional 1817/2500 (72.7%) High school/18–65 Maslach Burnout Inventory. Severe burnout, EE and DP: Internet addiction
Internet addiction was associated with severe burnout (10.5 vs. 2.7%, p < 0.001), moderate (36.8 vs. 1.7%, p < 0.001), and severe (6.3 vs. 0.1%, p < 0.001).
26.0% mild, 70.9% moderate, and 3.1% severe burnout.
Papastylianou et al., 2009 [3] Greece Cross-sectional 562/985 (57.1%) Primary/30–45 Maslach and Jackson, MBI: Maslach Burnout Inventory. EE: depressed affect, positive affect, degree of role clarity, role conflict and role ambiguity. EE: 25.09%, PA 14.27% and DP: 8.65%.
Hadi et al., 2009 [76] Malaysia Cross-sectional 565/580 (97.4%) Female/male
Mean age 40.5
Depression, Anxiety and Stress Scale (DASS 21) and Job Content Questionnaire (JCQ). Stress: age, duration of work and psychological job demands. 34.0% stress,
17.4% of teachers experienced mild stress.
Ratanasiripong et al., 2021 [40] Thailand Cross-sectional SS = 267 Primary/secondary
44.4
The Maslach Burnout Inventory for Educators Survey, Thai version (MBI-ES). Stress: marital status negative relation with stress., Family economics status, gender, sleep and resilience.
Burnout (EE): relationship quality and age.
DD: relationship quality and drinking.
PA: resilience and number of teaching hours.
6.0% had severe to extremely severe stress.
Szigeti et al., 2017 [50] Hungary Cross-sectional SS = 211 Primary/secondary 42.8 Hungarian version of the MBI–ES
General burnout/EE: overcommitment General burnout 58%, 13% for EE 11% for DP, and 17% for PA.
Hodge et al., 1974 [72] Wales, England Cross-sectional 107/145 (75%) Secondary, 33 mean Maslach Burnout Inventory (MBI) and
General Health Questionnaire (GHQ-60).
EE: difficulty of subject taught and satisfaction, age.
58% of music teachers thought subject was the most difficult subject to teach,
29% of mathematics teachers.
Music teachers have significantly higher EE and DP (high burnt) scores than mathematics teachers.
Music teachers.
Baka 2015 [73] Poland Cross-sectional 316/400/ (79%) Primary/secondary
22–60
The Oldenburg Burnout Inventory. Job burnout: age and job seniority, work hours, job demands.
Job burnout decreases along with age and job seniority.
Increased work hours were accompanied by job demands, general job burnout, depression and physical symptoms.
Not mentioned.
Othman et al., 2019 [131] Malaysia Cross-sectional SS = 356 Secondary <20->/= 50 Malay Depression Anxiety Stress Scales (DASS). Stress; gender, educational status, teaching experience, marital status. 32.3% stress symptoms
25.3% were mild to moderate. 7.0% severe to the extremely severe stress.
Female stress 32.7%, Indian/other ethnic 50.6%, lowest educational status 46.1%, longest teaching experience (34.6%), lowest income (33.9%), marriage duration 11–20 years (37.3%), 1–3 children (35.5%),
Skaalvik et al., 2020 [18] Norway Longitudinal SS = 262 High school Maslach Burnout Inventory-Educators Survey. EE: time pressure.
Cynicism: low student motivation.
Self-perceived accomplishment: autonomy and low student motivation.
Burnout: motivation to quit, job satisfaction.
Not mentioned
Li et al., 2020 [55] China Cross-sectional 1741/1795 (97%) Kindergartens/preschool 18–48 Chinese version Maslach Burnout Inventory and the Perceived Stress Scale-14. Burnout rate: overweight/obesity, type of school, income satisfaction,
depression.
Burnout: age, higher perceived stress levels, shorter years of teaching. Perceived stress (p < 0.001, OR = 1.15, 95%CI: 1.13–1.18).
Burnout was 53.2%. 53.0% (851/1607) in female subjects and 56.0% (75/134) in male subjects.
Gosnell et al., 2021 [57] Malaysia Cross-sectional 123/400(31%) Primary/secondary Depression Anxiety Stress Scales-21
self-care strategy questionnaire was adapted from a self-care scale in the Mental Health Handbook.
Stress: self-care.
The association was moderated by age. Among refugee teachers, women were more stressed than men. Stress: negative correlation with age. Younger teachers experienced higher rates of stress than older teachers.
Refugee teachers 8.3% in the severe or extremely severe stress levels clinical ranges.
Capone et al., 2020 [59] Italy SS = 285 High school 29–65 Burnout Inventory- General Survey (MBI). EE, and DP: flourishing participants languishing teachers. 22.1% for EE and 9.5% for DP.
Chan et al., 2002 [74] China Cross-sectional SS = 83 Secondary 22–42 The shortened 20-item Teacher Stressor Scale (TSS). e 20-item Chinese shortened version of the General Health Questionnaire (GHQ-20). Stress: psychological distress. Gender, age.
Self-efficacy: psychological distress, social support.
Not mentioned.
Zhang et al., 2014 [52] China Survey SS = 590 Primary/secondary 34 ± 8.11 Chinese Maslach Burnout Inventory. Reduced PA and intellectual burnout: somatization
EE, DP, and intellectual burnout: gender.
Burnout: gender, level of mental health.
EE, DP: best predictor anxiety.
EE accounted for 92.8% of the burnout cases, DP for 92.9%, reduced PA for 89.9%, and intellectual burnout for 95.0%). Burnout is more severe in female teachers than in male teachers.
Vladut, et al., 2011 [69] Romania Cross-sectional SS = 177 Primary/secondary/High 22–64 Maslach Burnout Inventory (MBI). Teachers’ Sense of Efficacy Scale. Burnout: rural or urban teaching, self-acceptance, classroom management, work-conditions and confidence. 49.6% above moderate or severe EE
28.7% on DP
54.1% on inefficacy.
Liu et al., 2021 [86] China Cross-sectional 449/500 (89.8%) High 36.70 Maslach Burnout Inventory (MBI). Job burnout: turnover intention; resilience has negative correlation.
EE was the most predictive factor for turnover intention with an explanatory variance of 29.2%, followed by DP with an explanatory variance of 1.9%
Lest is low PA with 1.5%.
Not mentioned.
Fimian et al., 1983 [44] US Survey 365/800(47%) Special education Teacher Stress Inventory (TSI) Survey. Sources of Stress (25 items); Emotional and Behavioral Manifestations of Stress (24 items); Physiological Manifestations of Stress (16 items). Stress: lack of time to spend with individual pupils, teaching. Special needs, or mixed ability students.
Increased workload, feeling isolated, and frustrated because of poor administration attitudes and behaviors.
87.1% moderately-to-very stressful. (45.6%) much-to-very-much stress. 15.9% (58/365) identified as low-stress, (68.4% (250/365) as moderate-stress, and 15.6% (57/365) as high-stress teachers.
Katsantonis 2020 [39] * 15 Countries. Survey SS = 51,782 Primary Self-efficacy is domain-specific and three scales reflect the self-efficacy. 5 items scale was designed by OECD (2019) to measure factors that cause workload stress. Workload stress: self-efficacy in instruction, student-behavior, workplace well-being, work satisfaction.
Stress: perceived disciplinary climate. School climate negative effect.
Increase work satisfaction results in perceived less stress. 16% (organizational constraints as a predictor of depression).
Japanese participants had greater levels of workload stress than Korean participants.
Participants from Belgium perceived greater workload stress.
Ratanasiripong et al., 2020 [88] Japan Cross-sectional 174/200 (87%) Primary/secondary 41.65 Japanese version of depression, Anxiety, and Stress scale (DASS-42).
Japanese version of the Connor–Davidson Resilience Scale (CD-RISC). Japanese version of the Rosenberg Self-Esteem Scale (RSE).
Stress: resiliency and self-esteem. Strength
Higher self-esteem and resilience were significantly correlated to less stress.
Not mentioned.
Jurado et al., 2005 [82] Spain Cross-sectional 496/602/ (82.7%) Primary/secondary (women, 45.3 ± 9.8; men, 44.7 ± 9.7). Spanish version of Epidemiologic Studies Depression scale (CES-D). Job stress: negative correlation with job satisfaction, desire to change job and appraisal by others. Teachers wishing to change jobs (25%; significantly higher score on job stress but low on job satisfaction and appraisal by others.
Bianchi et al., 2021 [132] France Spain Switzerland Survey France (N = 4395), Spain (N = 611), and Switzerland (N = 514) Schoolteachers Maslach Burnout Inventory for Educators.
Job strain was measured with a shortened version of the Effort-Reward Imbalance Questionnaire.
Burnout: neuroticism prediction (28–34%), job strain (10–12%), skill development, security in daily life, and work–non-work conflict (about 15–18%), sex, age, unreasonable work tasks, workhours, job autonomy, sentimental accomplishment, leisure activities, personal life support. Not mentioned.
Bianchi et al., 2014 [60] France Analytical SS = 5575 School teachers 41 years; Maslach Burnout Inventory.
Depression was measured with the 9-item depression scale of the Patient Health Questionnaire (PHQ-9).
EE: Strongly associated with depression than with DP and reduced PA. No-burnout 13% (750) participants.
Hammen et al., 1982 [43] US Cross-sectional SS = 75 Secondary DASS-21scale.
Bruno’s Teacher stress Inventory
Stress: depressive symptomatology, days off work, school-related factors. 76% moderate or greater stress
20% level of stress was “almost unbearable.”
Méndez et al., 2020 [25] Spain Cross-sectional 210/300 (70%) 30 to 65 Maslach burnout inventory. Burnout: correlates with EE, PA and DP resulting in three burnout profiles (high burnout); (moderate burnout) and (low burnout).
Burnout: depressive symptomatology.
The higher the burnout the greater the depressive symptomatology
33.3% high burnout
39.1% low burnout and 27.6% moderate burnout.
Jepson et al., 2006 [85] UK Cross-sectional 95/159 (60%) Primary/secondary Perceived Stress Scale (PSS). 10 scale item, occupational commitment 6 scale item. Work-related stress, strongest predictor and negative relationship, was occupational commitment, achievement striving experience, level taught.
Educational level taught. Occupational commitment increases, perceived stress decreases.
Significantly higher levels of perceived stress were reported from primary school teachers than secondary school.
Higher achievement striving experience have higher levels of perceived stress.
Al-Gelban 2008 [96] Saudi Arabia Cross-sectional 195/189 (96.9%) Male 28–57 Depression, Anxiety and stress DASS-42 scale. Depression, anxiety and stress were strongly positively and significantly correlated. 31% had stress.
Lee et al., 2020 [120] Malaysia Cross-sectional SS = 150 Secondary/primary DASS-21 inventory. Stress: number of years working. Majority of teachers with stress: either severe and extremely severe level are those working for 11 to 15 years. 10.7% stress.
Bounds et al., 2018 [111] US Survey 108/117 (92%) Primary/secondary 42 Teacher Stress Inventory (TSI). Stress: violence against, urban, suburban, and rural setting. Urban teachers had the highest levels of stress from violence rather than suburban teachers.
Pressley et al., 2021 [56] US Survey SS = 329 Elementary The COVID Anxiety Scale. A teacher burnout subscale of stress. Stress: anxiety factors in pandemic situations. Not mentioned.
Yaman 2015 [93] Turkey Survey SS = 436 Elementary/branch 35.2 Mobbing Scale and the Stress subscale of the Depression Anxiety Stress Scale. Turkish version of the Stress Subscale of DASS. Stress: predicted positively by humiliation, discrimination, communication barriers, and mobbing scores. Increment in mobbing will increase stress.
Cook et al., 2019 [83] US Cross-sectional 180/105/58.5% Middle 22 ± 37 Teacher Stress Inventory. The Daily Spiritual Experience Scale. Stress: teacher spirituality.
As teachers’ spirituality increases, their time-management stress and their work-related stress increase.
Not mentioned.
Okebukolal 1992 [75] Nigeria Survey SS = 368 Science The Occupational Stress Inventory for Science Teachers (OSIST). Stress: school villages (personnel relation dimension) curriculum, facilities, student characteristics, administrative, and professional growth and self-satisfaction, subject taught, science budget.
Science teachers in the rural schools mean stress score of 47.25 (SD = 4.89), urban schools mean stress score of 51.29 (SD = 6.95).
Urban teachers were found to be more stressed than those in rural areas. Female science teachers were more stressed than their male counterparts.
Klassen 2010 [77] Canada Survey 951/- (Approximately 75%) Elementary/secondary Teacher Stress Inventory. Collective Teacher Efficacy Belief Scale (CTEBS Job satisfaction was measured with a one-factor, three-item, 9-point Likert-type scale. Stress: collective efficacy, student behavior, gender, workload, class size. 21.3% females rated the stress from workload “quite a bit” or “a great deal” of stress from workload factors.
13.4% of male teachers rated stress from workload at a mean of 7 or higher. More women (18.6%) than men (12.8%) reported feeling “quite a bit” or “a great deal” of stress from student behavior.
Proctor et al., 1992 [45] UK Survey 256 (93%) Primary 39.68 Zigmond and Snaith’s 6 Hospital Anxiety and Depression (HAD) Scale and Moos and Insel’s7 Work Environment Scale (WES). Stress: anxiety, work overload, time pressures, stressors relating to pupils and parents. 67% found teaching ‘considerably’ or ‘extremely’ stressful, 79 (32%) ‘slightly’ stressful and 2 (1%) ‘not at all’ stressful.
Akin 2019 [63] Turkey Mixed research method 460/3478 (13%) Teachers Turkish version of the Maslach and Jackson inventory. DP: marital status.
Reduced PA: number of children.
Not mentioned.
Chan 1998 [125] Hong Kong Cross-sectional SS = 415 Secondary 21–61 Teacher stressor scale and the General Health Questionnaire. Stress: high support—less anxiety symptoms, psychological symptoms. 37.3% psychiatry morbidity.
Adeniyi et al., 2010 [78] Nigeria Cross-sectional SS = 50 Special Needs Job Stress Inventory. Stress: marital status, teaching special needs, lack of pupils’ progress in class work/academic achievement, societal attitudes/respect heavy workload and lack of help/assistance, degree and nature of disabilities of the special need children. Not mentioned.
Beer et al., 1992 [53] US Cross-sectional 86/92(93%) Grade and high school Beck’s Depression Scale, the Coopersmith Self-esteem Inventory—Adult Form, Stress Profile for Teachers, and the Staff Burnout Scale. Burnout and stress: gender, level taught-high/grade school.
Grade school teachers experienced more burnout than high school teachers.
Burnout scores higher for female high school teachers than for both male and female grade school teachers. Scores on stress were higher for male high school teachers than for both female high school teachers and male grade school teachers.
Liu et al., 2021 [98] China Cross-sectional 907/1004 (90.3%) Primary and secondary 20 ≥ 50 Generic Scale of Phubbing, the Maslach Burnout Inventory—General Survey, Ruminative Response Scale, and the Center for Epidemiological Studies Depression Scale.
Job burnout: phubbing significant positive effect on job burnout, depression.
The relation between job burnout and depression were moderated by rumination.
Not mentioned.
Shin et al., 2013 [95] Korea Survey SS = 499 Middle and high school Maslach Burnout Inventory–Educator Survey
Center for Epidemiological Studies Depression Scale.
Burnout: depression; baseline status of depression. Teacher’s burnout leads to subsequent depression symptoms, not vice versa. Not mentioned.
Genoud et al., 2021 [41] Switzerland Cross- sectional SS = 470 Secondary 24–63 Maslach’s burnout scale version validated by Dion and Tessier twenty-seven items
French; Depression Anxiety Stress Scales (DASS).
Burnout: negative affectivity (tendency to feel depression, anxiety, or stress), personal fulfillment.
Greater tendency to feel depressed result in teachers experiencing a lower level of personal accomplishment.
Two-thirds of the sample (N = 308) 66% of teachers below average for the three dimensions (stress, depression, and anxiety).
Steinhardt et al., 2011 [68] US Cross-sectional /267 (26%) High/Elementary/middle Mean 45 Maslach Burnout Inventory-Educators Survey (MBI-ES) Modified version of the Teacher Stress Inventory. Burnout: gender, experienced.
Stress: depressive symptoms.
Females reported greater chronic work stress and emotional exhaustion.
Total effect of stress on depressive symptoms, taking together the direct and indirect effects via burnout, accounted for 43% of the total variance.
Increased stress leads to increased burned out.
Pressley 2021 [58] US Survey SS = 359 Primary/secondary Teacher burnout scales. Burnout-stress: COVID-19 anxiety, current teaching anxiety, anxiety communicating with parents, and administrative support. High level of average teacher burnout stress score of 24.85.
Schonfeld et al., 2016 [64] US Survey SS + 1386 School teachers mean = 43 The Shirom-Melamed Burnout Measure, Depression module of the Patient Health Questionnaire. Burnout and depressive symptoms were strongly correlated.
Burnout and depressive symptoms: stressful life events, job adversity, and workplace support. Burnout: anxiety.
86% of the teachers identified as burned out met criteria for a provisional diagnosis of depression. Fewer than 1% in the no-burnout group.
Not mentioned
Bianchi et al., 2016 [92] New Zealand Cross-sectional SS = 184 School teachers Mean 43 Shirom–Melamed Burnout Measure (SMBM)
Depression was assessed with the PHQ-9.
Burnout: strongly correlation. Depressive symptoms, moderately correlated with dysfunctional attitudes, ruminative responses, and pessimistic attributions. Depression “low burnout-depression”, (n = 56; 30%),
“Medium burnout-depression” (n = 82; 45%),
“High burnout-depression” (n = 46; 25%).
(About 8%) reported burnout symptoms at high frequencies and were identified as clinically depressed.
Desouky and Allam 2017 [28] Egypt Cross-sectional SS = 568 High 39.4 ± 8.7 Arabic version of the Occupational Stress Index (OSI), the Arabic validated versions of Taylor manifest anxiety scale and the Beck Depression Inventory. OS: Anxiety and depression scores, age, gender, higher qualifications and higher workload. OS, anxiety and depression scores were significantly higher among teachers with an age more than 40 years, female teachers, primary school teachers, higher teaching experience. OS, anxiety and depression, respectively. 100%, 67.5% and 23.2%,
Private schools show a significantly higher prevalence of moderate and severe OS compared to governmental schools (31.6% and 68.4% vs. 22.4% and 67.1%).
Jones-Rincon et al., 2019 [65] US Cross-sectional 3003/3361(89%) Elementary, middle/junior high or high Patient Health Questionnaire. Job satisfaction was measured with 10 items. Perceived stress levels: anxiety disorder.
Teachers with anxiety disorder reported having higher perceived stress levels.
Not mentioned.
Kinnunen et al., 1994 [51] Finland Survey 1012/1308/ (77%) High/vocational/special/Physical/secondary 45–59 Maslach and Jackson’s inventory. EE: gender.
Poor work ability. Women exhibit higher scores for EE.
Not Mentioned
Martínez et al., 2020 [46] Spain Random Sampling 215/300 (71.7%) Primary 30 to 65 years M = 44.89 The Maslach Burnout Inventory (MBI), Zung Self-Rating Depression Scale (SDS), Coping with Stress Questionnaire. Burnout: depressive symptomatology, and quality of interpersonal relationships. 48.37% low levels of EE, 25.12% high levels of PA, (b) high levels of EE and DP, and (c) 26.51% low levels of DE and PA.
Capone et al., 2019 [70] Italy Cross-sectional SS = 609 High school, middle school, elementary and primary school. 27 to 65, mean = 48.35 The Center for Epidemiologic Studies Depression Scale (Italian version. The Italian version of the Maslach Burnout Inventory-General Scale. The Teacher Self-Efficacy Scale. Burnout: collective efficacy, school climate, and organizational justice and relationship.
EE and cynicism functioned as significant mediators between the three predictors (opportunities, organizational relationships, and organizational justice) and depression.
Not mentioned.
Aydogan 2009 [84] Turkey N = 83
Germany N = 78
Cyprus
N = 74
Cross-sectional 255/306 (83%) High M = 38 ± 6.96, 37.9 ± 6.74, 45.8 ± 10.42 Shirom–Melamed Burnout Measure. Turkish version of Minnesota Job satisfaction scale. Burnout: country working, job satisfaction, depression.
Cyprus teachers 57% of the variance in burnout explained by depression.
58% of the variance in burnout explained by job satisfaction and anxiety.
Germany 575% variance in burnout explained by job satisfaction.
Not mentioned.
Belcastro et al., 1983 [49] US Cross-sectional 428/359 (84%) Public The Maslach Burnout Inventory and the Teacher Somatic Complaints and Illness Inventory. burned-out: somatic complaints More than 11% burned out.
246 (68.5%) not burned-out.
Capel 1992 [89] UK Cross-sectional 640/405/63.3% Middle, upper, high school The Maslach Burnout Inventory. The Taylor Manifest. Stress and burnout: role conflict, and role ambiguity, High anxiety.
Highest stress level: high workload demands after-school time, lack of recognition for extra work, too much paperwork. Students’ behavior. Burnout: anxiety.
Not mentioned.
Ptacek et al., 2019 [54] Czech Republic Cross-sectional SS = 2394 Primary 18–72 Questionnaire survey: anamnestic part and Standardized questionnaires: SVF 78, SMBM, ENRICHD SSI, BDI II, USE. Burnout: length of teaching/employment, healthy lifestyle. Cognitive burnout: age and length of teaching employment. Those with healthy lifestyle (work–life balance) have significantly lower burnout rates. Males–higher emotional burnout, females–higher physical burnout rates). 18.3% of participants felt definitely threatened by burnout syndrome, 34.9% may be, 9.9% definitely not threatened by burnout syndrome. Long-term stress 21.8%, compared to the (7.5%) do not experience long-term stress.

* Katsantonis 2020 (15 countries)—Japan and Korea form the East-Asian model. France and Spain form the Latin model. Denmark and Sweden form the Northern model. Australia and the United Kingdom represent the Anglo-Saxon model and finally, Belgium and the Netherlands form the Germanic model. Sample Size: SS; Emotional Exhaustion: EE; Personal Accomplishment: PA; Depersonalization: DP; Occupational Stress: OS; Sense of Coherence: SOC; Science Stream: SCIS; Art Stream: AS.