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. 2026 Jul 20;35(5):e70401. doi: 10.1111/jsr.70401

The Development of the European Sleep Questionnaire A New Patient‐Reported Outcome Measure

Dirk A Pevernagie 1,2,✉, Marie De Bruecker 1,3,4, Elke Veirman 4, Geert Crombez 4, Dimitri M L Van Ryckeghem 4,5, Katrien Hertegonne 6, Fré A Bauters 6, Inger L Abma 7, Erna Sif Arnardottir 8, Ludger Grote 9,10, Jan Hedner 9,10, Anna Sigridur Islind 11, Kamilla Rún Jóhannsdóttir 12, Gert Jan Lammers 13,14, Walter T McNicholas 15, Piet‐Heijn van Mechelen 16, Kristín Anna Ólafsdóttir 8, Sebastiaan Overeem 17,18, Dieter Riemann 19,20, Reijo Sund 21,22, An Mariman 3,23,24
PMCID: PMC13619087  PMID: 42473734

ABSTRACT

Sleep medicine relies on patient‐reported outcome measures (PROMs) to complement clinical interviews and objective sleep tests. Available sleep questionnaires focus on isolated symptoms or single disorders, limiting their ability to capture the complexity of sleep conditions. Also, many PROMs remain poorly validated. The European Sleep Questionnaire (ESQ) is being developed as a generic transdiagnostic sleep PROM designed to address these limitations. By integrating relevant interview components, it aims to streamline clinical assessment and better reflect real‐world phenotypes across the full spectrum of sleep disorders. The ESQ has been initiated within the EU‐funded Sleep Revolution project and is still being developed through an iterative process. Its design is informed by a comprehensive literature review as well as expert and patient input. The ESQ prototype contains 119 items organized into nine sections and uses Likert‐type scales to assess symptom severity, frequency, and bothersomeness over the past month. It is equipped with an additional module for follow‐up assessment. It is translated into 17 languages and is digitally implemented to support multicenter studies. Initial validation includes cognitive interviews and evaluation of psychometric properties in patients with various sleep disorders. Item refinement and scoring key creation will guide the further development of the ESQ, after which it will be made available for public use. The ESQ aims to support personalized clinical diagnosis and appraisal of treatment results. Future research will extend into other sleep disorders and specific populations, strengthening the ESQ as a comprehensive tool for clinical practice, research, and preventive strategies.

Keywords: generic questionnaire, patient‐reported outcome, sleep disorders, Sleep medicine, transdiagnostic assessment

1. Background

Sleep medicine is emerging as an established clinical specialty, drawing strength from its interdisciplinary roots in diagnosing and managing a wide range of sleep disorders (Pevernagie et al. 2025). While the clinical relevance of these disorders has long been recognized (Schulz 2022), only recent advances have uncovered the complex mechanisms that drive these conditions (Joiner 2018). By linking research with clinical application, the foundations for personalized sleep medicine are now firmly established.

Diagnostic assessment is fundamentally based on documenting patients' reported experiences and conducting physiological sleep evaluations, complemented by other clinical tests. However, inconsistencies between polysomnographic findings and patients' reported symptoms are commonly observed. Such discrepancies have been described in obstructive sleep apnea (OSA) (Kaplan et al. 2017; Pevernagie et al. 2020; Weaver et al. 2005), but are not limited to respiratory sleep disorders. In chronic insomnia, diagnosis relies mainly on clinical history, as polysomnographic findings are not always in line with what patients report (Riemann et al. 2023).

Rich, nuanced information on patients' experiences is typically obtained from clinical interviews and various sleep questionnaires, ideally supplemented by a sleep diary (Arnardottir et al. 2021). This information often helps to shape a preliminary diagnosis or to identify key components of the differential diagnosis. However, conducting a clinical interview by a sleep specialist is time‐consuming (Fischer et al. 2012). Because sleep specialists are few and waiting times are long, timely expert care may not be available to many patients (van Mechelen et al. 2021). A comprehensive, digitally administered sleep questionnaire could help to acquire the required information. Although not intended to replace the clinical interview, such an instrument could provide healthcare professionals with a detailed overview of patients' sleep patterns and disturbances, thereby streamlining the path to effective assessment (Arnardottir et al. 2021). Moreover, due to the rising adoption of digital technology worldwide, digitally administered PROMs are becoming increasingly established in clinical practice and research (Meirte et al. 2020).

A wide range of sleep questionnaires is available for use in both research and clinical practice (Shahid et al. 2012). Many of these aim to either quantitatively assess symptom severity or to evaluate how sleep disorders may affect perceived quality of life, or both. For example, the Epworth sleepiness scale (ESS) gauges sleep propensity reflecting the severity of daytime sleepiness (Johns 1991), whereas the functional outcomes of sleep questionnaire (FOSQ) measures how sleepiness interferes with daily activities (Weaver et al. 1997). The Insomnia Severity Index (ISI) expands the severity assessment of insomnia, the main symptom, with questions about daytime consequences, (dis)satisfaction, worrying and impaired quality of life noticed by others (Morin et al. 2011). However, symptom severity and impact on quality of life should not be equated as they are often not aligned. For example, some patients report excessive sleepiness, but are not concerned about it. Therefore, both aspects should be addressed separately.

Sleep PROMs can be broadly categorized into generic questionnaires, applicable across a range of sleep health contexts, and questionnaires with narrower scope. The latter either target only symptoms, such as sleepiness or sleeplessness, or focus on sleep disorders associated with presumed specific symptom patterns (e.g., OSA or restless legs syndrome, among others) (Pevernagie et al. 2021).

Disorder‐based PROMs frequently contain symptoms that also appear in sleep disorders with different underlying pathophysiological mechanisms. These symptoms are therefore nonspecific. When respondents endorse these symptoms in such questionnaires, it is implicitly assumed that they are attributable to the disorder under evaluation. However, this presumption does not always hold. A typical example is excessive daytime sleepiness in OSA, which may actually stem from other factors—most commonly, a behavioral lack of sleep (Kallweit et al. 2022). Because disorder‐specific PROMs presuppose that the assessed symptoms are attributable to the suspected diagnosis, they may lead to misattribution and thereby introduce nosological bias (Pevernagie et al. 2021).

In the absence of a comprehensive transdiagnostic PROM, clinicians often administer several questionnaires to assess different dimensions of sleep and wakefulness, such as sleeplessness, sleepiness, and fatigue, or condition‐specific complaints like snoring, apneas, and restless legs. However, such a fragmented approach is suboptimal because these questionnaires differ in design, underlying assumptions, and measurement frameworks. As a result, their findings are difficult to integrate into a coherent clinical profile.

While the combined use of multiple narrowly focused PROMs may align with good clinical practice, a unified measurement framework offers important psychometric benefits, including reduced construct and measure proliferation (Flake and Fried 2020), improved comparability through measurement invariance (Putnick and Bornstein 2016), and consistency with contemporary dimensional approaches to classification and assessment (Kotov et al. 2017). Generic instruments may be less sensitive to certain disorder‐specific features, yet they provide a coherent and psychometrically robust basis for broad, transdiagnostic evaluation.

Although multidimensional sleep questionnaires have been developed for research (Arnardottir et al. 2021; Keenan et al. 2018) and for clinical applications, a comprehensive PROM covering the diversity of real‐world phenotypes is still lacking. For example, the Pittsburgh Sleep Quality Index (Buysse et al. 1989) assesses seven domains, including sleep quality, latency, duration, efficiency, disturbances, medication use, and daytime dysfunction. The Medical Outcomes Sleep Study Measure (Hays et al. 2005) evaluates sleep disturbance, adequacy, somnolence, snoring, nocturnal dyspnea or headache, and sleep quantity. The Iowa Sleep Disturbances Inventory (Koffel and Watson 2010) covers a broad spectrum of complaints, including insomnia, fatigue, fragmented and nonrestorative sleep, nightmares, nocturnal anxiety, movement‐ and sensation‐related symptoms, hypersomnolence, and irregular sleep schedules.

However, multidimensional PROMs should transcend a mere enumeration of sleep and wake symptoms. To capture the broad spectrum of sleep experiences and disorders, such instruments should be structured around key conceptual domains (see Box 1). In keeping with these principles, the European Sleep Questionnaire (ESQ) was developed as a novel PROM in sleep medicine within the EU‐funded Sleep Revolution consortium project (Arnardottir et al. 2022). The ESQ extends existing instruments in several important respects. It provides greater definition by distinguishing symptom frequency, intensity, and bothersomeness. It also integrates contextual and personal factors—such as pain, rumination, environmental influences, and impact on bed partners—that have not previously been combined within a single instrument. In addition, the ESQ includes modules addressing sleep profiles, patient beliefs and expectations, and post‐treatment follow‐up.

BOX 1. Key features of a generic PROM for sleep disorders.

The instrument should:

  • Be patient‐centered, capturing symptoms, contextual and personal factors, and behaviors affecting both the patient and others;

  • Detect common symptoms across different sleep conditions without presuming underlying diagnoses;

  • Assess symptom severity, bothersomeness, and impact on wellbeing;

  • Be sensitive to change over time, including treatment effects;

  • Balance comprehensiveness with feasibility for routine use;

  • Support digital application and integration with complementary data sources such as sleep diaries, clinical interviews, and objective sleep tests.

The present paper describes the development and current status of the ESQ. The multi‐phase development and validation process of the ESQ is documented, offering methodological transparency. The ESQ prototype is introduced, along with its implementation in a multi‐lingual, multi‐centre digital research infrastructure. This paper thereby establishes the methodological foundation for ongoing and future validation studies of the ESQ.

2. Developmental Framework

The development of the ESQ is part of the Sleep Revolution research project, funded by the EU's Horizon 2020 research and innovation programme under grant agreement no. 965417 (Arnardottir et al. 2022).

The ESQ sub‐project is still ongoing and is led by a core team of expert physicians and psychologists at Ghent University. The span of expertise includes knowledge of questionnaire methodology, health psychology and sleep medicine. During several development stages, input was and will further be obtained from an Advisory Board consisting of an international panel of experts. This body includes members of the “Apneuvereniging”, that is, the Dutch sleep apnea patient organization (https://apneuvereniging.nl).

The development of the ESQ consists of six phases, that is, design, creation, translation, implementation in the research environment, initial validation, and completion. This process is inherently iterative, involving continuous back‐and‐forth refinement. It involves multiple activities, some of which have already been finalized, whereas others are currently in progress, or will be undertaken in the near future (see Figure 1). An overview of the phases and their corresponding publications is provided in Table 1.

FIGURE 1.

FIGURE 1

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Developmental phases and time dimension of the ESQ.

TABLE 1.

Phases in the development of the ESQ and their corresponding publications.

Phase Manuscripts
Literature review of PROMs

  • The development quality of generic sleep questionnaires from a COSMIN perspective: Systematic review and call for action

  • What do patient‐reported sleep measures assess? A content analysis
Stakeholders' surveys

A transdiagnostic core set for sleep disorders:

A qualitative patients and experts study
Development overview and release ESQ prototype

The development of the European Sleep Questionnaire:

A new patient‐reported outcome measure
Psychometric validation

Validation of the European Sleep Questionnaire:

A network psychometric approach
Cognitive interviews

The European Sleep Questionnaire:

A cognitive interview study
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The ESQ was released as a prototype for use within the Sleep Revolution project and is also applied for research purposes at the Ghent University Hospital in Belgium (see Supporting Information).

2.1. Design

The development of a conceptual framework portraying key concepts relevant to sleep disorders was initiated in October 2021. The design involved six iterative activities: (1) conducting a literature review of existing sleep PROMs, (2) appraising the content validity of the identified PROMs, (3) compiling a database of domains and items of these instruments, (4) surveying the Advisory Board members to examine the relevance of the core domains represented in these PROMs and identification of missing domains, (5) surveying patients and sleep specialists to generate item content across core domains, and (6) creating the final framework comprising a transdiagnostic set of sleep domains.

2.1.1. Review of the Literature on Existing Generic Sleep PROMs

The literature review aimed (1) to identify studies focusing on generic or disorder‐specific sleep questionnaires in adults, (2) to identify questionnaires, and (3) to map content domains, items and response options assessed by these questionnaires. Details regarding search methods, inclusion and exclusion criteria are provided in Veirman et al. (Veirman et al. as yet unpublished data) and on Open Science Framework [OSF; (Veirman et al. 2023) https://doi.org/10.17605/OSF.IO/NPGK6].

2.1.2. Appraisal of the Content Validity of the Identified PROMs

As an additional line of investigation we appraised the quality of the content validity evidence in the development of generic sleep PROMs using the consensus‐based standards for the selection of health measurement instruments (COSMIN; (Mokkink et al. 2024)). We observed that the development of generic sleep PROMs often does not comply with current state‐of‐the‐art standards. Of concern, patient input was largely insufficient during their development (Veirman et al. as yet unpublished data). We also performed a content mapping of the items of these generic sleep PROMs using the linking procedures of the International Classification of Functioning, Disability and Health (ICF; (Cieza et al. 2002; Cieza et al. 2019; Cieza et al. 2005)). This research was complemented with a semantic analysis of items. We observed that generic sleep PROMs generally fall short in capturing the multidimensional nature of sleep, as they tend to only focus on specific symptoms while disregarding personal factors, contextual factors, and the impact on daily functioning and social interactions (De Bruecker et al. 2026).

2.1.3. Compilation of a Database of Domains and Items

The domains and items from questionnaires retrieved via this systematic review were compiled in Microsoft Excel for aggregation purposes, whereby similar domains were reduced by grouping them (e.g., ‘sleep latency’, ‘difficulty in falling asleep’ and ‘ease of getting to sleep’) and assigned to broader categories (e.g., ‘symptoms of nocturnal sleep’). Likewise, the domains ‘sleepiness’, ‘daytime sleepiness’, ‘excessive daytime sleepiness’ and ‘daytime somnolence’ were grouped under ‘daytime functioning’. This resulted in a blueprint of relevant domains (e.g., sleep initiation). Next, domains were organized into four overarching categories, that is, context (internal or external factors disrupting or preventing sleep), symptoms of nocturnal sleep, daytime functioning, and treatment. In parallel, items were compiled per domain and reduced according to a predefined set of reduction criteria, including semantic overlap (e.g., similar content), generic information (e.g., sociodemographic information) and content‐related issues (e.g., container items). This process resulted in a curated item pool and a blueprint of domains serving as a conceptual basis for developing the ESQ.

2.1.4. Refining the Domain Structure Through Advisory Board Review

To evaluate the relevance and completeness of the emerging conceptual framework, we conducted an online survey among members of the Advisory Board. Participants were presented with key domains related to nocturnal sleep and daytime functioning, each illustrated with an example item derived from the curated domain and item pool. Members rated the importance of each domain on a 1–10 Likert scale (anchors), with scores of ≥ 7 indicating relevance. In total, 48 of the 83 domains met this threshold. The core team used this list as a starting point for discussion regarding the inclusion or exclusion of domains in the ESQ.

Certain domains—such as taking special measures to stay awake—were retained because of their clinical relevance. Some domains were retained because of their clinical relevance, despite receiving lower ratings (e.g., sexual functioning). Other domains were excluded for different reasons. Some were captured with other methods (e.g., sleep efficiency via sleep diaries). Others were too narrowly formulated or overlapped with broader domains (e.g., working effectively in afternoon). Finally, some domains fell outside the intended scope of our PROM, or were deemed redundant (e.g., alertness). Discussion of the findings within the core team and with the Advisory Board led to a final list of retained domains.

2.1.5. Broader Stakeholder Consultation

The purpose of this activity was to obtain broader stakeholder input to generate item content and further refine the retained domains. To this end, we conducted an online survey involving patients with diverse sleep complaints as well as sleep clinicians and other experts not included in the Advisory Board. We recruited 65 patients across a range of clinical diagnoses (sleep apnea, insomnia, narcolepsy, and other hypersomnolence disorders, restless legs syndrome, and parasomnias). The group of experts consisted of 16 sleep practitioners from different disciplines (pulmonologists, psychologists, psychiatrists, and neurologists).

The participants filled out an online open‐ended survey addressing sleep disturbances, its influencing factors, and sleep‐related daytime impairments. Patients were asked to describe their own experiences, whereas clinicians were asked to report the experiences patients commonly describe during consultations.

Data were evaluated using a qualitative content analysis. Results were segmented into units (codes) and organized into two main categories and subcategories. The coding scheme followed a mixed methods approach, combining predefined categories that paralleled the conceptual framework structure and additional categories that emerged inductively from the data. The findings informed the iterative shaping of the conceptual framework, drawing on lived patient experiences and clinical practice. The results of this qualitative study will be published in a separate paper.

2.1.6. Transdiagnostic Conceptual Framework

The above steps resulted in a conceptual framework with a set of domains across different sections, including several main categories and subcategories: medical history (e.g., mental disorders), stressors (e.g., financial problems), sleep profile (e.g., chronotype), factors affecting sleep (e.g., bodily sensations), sleeping behaviours affecting others (e.g., limb movements), sleep disturbances (e.g., sleep initiation problems), and daytime impairments (e.g., sleepiness). The full development of this framework will be described in more detail in a separate publication.

2.2. Creation of the ESQ

The development of the ESQ was guided by the transdiagnostic framework providing the conceptual foundation for defining the content domains. These domains were assigned to corresponding ESQ sections, such as assigning sleep initiation problems to nocturnal sleep, sleepiness to daytime functioning, and environmental factors to factors affecting sleep. In parallel, the curated item pool derived from the reviews of existing PROMs offered inspiration for the scope of the domains and the formulation of item wording.

Key design decisions were made pertaining to purpose, scope, domains, items, and visual layout of the questionnaire. The core structure of symptoms assessment was defined in terms of frequency, intensity, and bothersomeness. For some symptoms, intensity was represented by describing the symptom in different situations with increasing levels of severity. A pool of items was created, refined, and classified into domains based on consensus among the core team.

The ESQ was designed to be re‐administered after treatment to evaluate changes in patients' experiences and symptom scores. However, given its length, it was anticipated that some users might be reluctant to complete the questionnaire a second time. Therefore, it was deemed appropriate to develop an additional brief module specifically for follow‐up assessment. This instrument can be administered alongside a re‐administration of particular ESQ sections (my sleep profile, factors affecting my sleep, my sleep affecting others, my nocturnal sleep and my daytime functioning), or can be used as a stand‐alone tool. It probes changes in overall nocturnal sleep and daytime functioning by asking respondents to compare their current status with their condition prior to treatment initiation. In addition, it includes items addressing treatment characteristics and potential treatment‐related side effects.

The prototype of the ESQ consisted of 119 items distributed across 9 sections. A one‐month period was selected as the recall period for patients to answer the questions. Frequency and bothersomeness questions were rated on five‐point Likert scales (1 = never to 5 = always, and 1 = not at all to 5 = very much, respectively). The section ‘my sleep affecting others’ was presented only if participants indicated they have a bedpartner. The estimated completion time for the full ESQ is between 15 and 30 min. To reduce respondent burden, the digital platform allows participants to save their completed progress and complete the questionnaire across multiple moments. The structure of the ESQ is presented in Table 2.

TABLE 2.

Structure of the ESQ.

# Section # of items Domains
a General information 19

Personal information

Personal profile

General health

Current stressors
b My help request 8

Nature, duration and progression of problems

Beliefs

Expectations

Previous treatments
c My sleep profile 11

Sleep pattern

Sleep habits

Chronotype
d Factors affecting my sleep 34

Bodily sensations

Emotions

Thoughts

Environmental/external
e My sleep affecting others 9 Sleeping behaviours
f My nocturnal sleep 5

Sleep initation

Sleep maintenance

Morning awakening

Nonrestorative sleep
g My daytime functioning 19

Sleepiness

Drowsiness

Fatigue

Cognition

Emotions

Other (social interactions, sexual functioning, muscle weakness, daily activities, etc.)
h Final comments 5

Help with filling out the questionnaire

Overall rating of sleep

Overall rating of daytime functioning

Additional information
i Treatment module 9

Overall change and sleep health

Treatment: adherence, side effects and effectiveness
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2.3. Cross‐Cultural Translation of the ESQ

The ESQ was first developed in English. It was forwarded for translation to the consortium members, as the questionnaire had to be administered in the primary languages of the participating research centres. The proposed translation procedure was adapted from the Functional Assessment of Chronic Illness Therapy (FACIT; www.facit.org/) methodology (Bonomi et al. 1996; Eremenco et al. 2005). It was recommended to comply with instructions for translation and backtranslation as outlined in Box 2.

BOX 2. Instructions for translating the ESQ forward and backward.

  1. Forward Translation: The English ESQ is translated into the target language by two native‐speaking translators (V1 and V2).

  2. Reconciliation: A third native‐speaking translator reviews V1 and V2 and reconciles them into a single version (V3). This process may involve selecting one translation, merging both, or creating a new version.

  3. Back‐Translation: V3 is translated back into English by a native English‐speaking translator fluent in the target language, who has no prior exposure to the original ESQ.

  4. Quality Control: The back‐translation is compared to the original ESQ to identify any discrepancies or incorrect translations.

  5. Review: Three native‐speaking experts review all previous steps to select the most accurate translation for each item, or to propose alternate translations.

  6. The pre‐final version is evaluated, with agreement on each item. The final version is then checked by an independent proofreader.

The English version of the ESQ was translated into Croatian, Czech, Dutch, Estonian, Finnish, French, German, Greek, Icelandic, Italian, Norwegian, Polish, Portuguese, Romanian, Swedish, and Turkish.

2.4. Implementation in the Research Environment

The ESQ was integrated into the SleepWell digital platform, whose development represented a key component of the Sleep Revolution project. The platform was designed to collect, process, and integrate heterogeneous data from multiple sources into a standardized database structure, while enabling the longitudinal storage of repeated sleep assessments (Sveinbjarnarson et al. 2023). The portal also provides patients, clinicians, and researchers with secure access for data entry and retrieval.

Co‐design principles were used to guide the digitalisation of the ESQ (Schmitz et al. 2025). Empirical data were collected using several user‐centred methods, including the think‐aloud method (where participants are asked to use the digitally administered PROM while uttering their thoughts), the Five‐act interview, as well as two standardized questionnaires: the System Usability Scale (assessing usability) and AttrakDiff (assessing user experience). A prototype of the digitally administered ESQ was subsequently evaluated within the core group, the advisory board, and a sample of 17 test persons. Usability and user‐experience assessments yielded favourable results (Lilliendahl 2022).

The implementation of the ESQ within this framework enables secure multicentric data collection via a web‐based interface accessible remotely by patients. Participants complete the questionnaire digitally via a user‐friendly interface that has been shown to deliver a high user experience, facilitating accessibility and reducing missing data through automated completion checks and real‐time input validation.

In addition to patient‐facing administration, the digital platform includes a clinician and researcher dashboard that allows authorized users to monitor questionnaire completion and visualize symptom trajectories over time (see Figure 2). Repeated administrations can be scheduled automatically, enabling longitudinal follow‐up and assessment of treatment response or symptom evolution. The centralized architecture also supports harmonized data collection across multiple participating centres, thereby improving data consistency and facilitating collaborative clinical research.

FIGURE 2.

FIGURE 2

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Visual user interface of ‘Factors affecting my sleep’ and ‘My nocturnal sleep’.

The application of the ESQ within the SleepWell platform extends the ESQ's utility beyond traditional paper‐based PROMs and supports its use in routine care, multicenter studies, and real‐world observational settings. The ESQ prototype is currently available in 17 languages.

2.5. Initial Validation of the ESQ

The validation methodology was guided by key literature on questionnaire‐based health assessment (Haynes et al. 1995; Kirshner and Guyatt 1985; Streiner et al. 2024; Van Ryckeghem and Crombez 2022), and by guidelines on PROM development and assessment of measurement properties (Gagnier et al. 2025; Mokkink et al. 2010; Terwee et al. 2018). Validation activities focused first on content validity, followed by psychometric evaluation in clinical cohorts.

2.5.1. Cognitive Interviews

Content validity was evaluated through cognitive interviews designed to assess the comprehensibility, relevance, and comprehensiveness of the ESQ items, response options, and instructions. A semi‐structured interview guide was used to ensure systematic evaluation of these aspects (DeWalt et al. 2007; Willis and Artino Jr. 2013). The interviews were conducted with 11 patients who also participated in the psychometric validation study of Ghent University Hospital. To attain demographic diversity, sampling included balanced gender representation, non‐Belgian ethnicity, age over 65 years, and lower education levels. The interviews are to be transcribed and systematically coded using the Question Appraisal System, a framework for identifying problematic question features, supplemented by data‐driven bottom‐up codes (Willis 2015; Willis and Lessler 1999). Identified issues will inform a list of recommendations for item, response option, and instruction revision and will be taken into account as we move from the ESQ prototype to a next version.

2.5.2. Psychometric Validation

For psychometric validation, the ESQ was administered in two cohorts of adult patients with sleep disorders. First, the ESQ was used in different prospective studies of the Sleep Revolution project. Patients referred for suspected OSA were asked to fill out the ESQ on the Sleep Well digital platform. In addition, common sleep questionnaires, including the Insomnia Severity Index (ISI) (Bastien et al. 2001), Fatigue Severity Scale (FSS) (Krupp et al. 1989), Epworth Sleepiness Scale (ESS) (Johns 1991), Pittsburgh Sleep Quality Index (PSQI) (Buysse et al. 1989), and other questionnaires including the Depression, Anxiety and Stress Scale—21 Items (DASS‐21) (Antony et al. 1998) and Patient Global Impressions Scales for severity and improvement (PGI‐S and PGI‐I) (Guy 1976) were administered via REDCap. All PROMs were re‐administered 3 months after CPAP treatment initiation.

Second, parallel validation studies are ongoing at the Departments of Respiratory Medicine and Psychiatry at Ghent University Hospital. Participants are adults with sleep‐related complaints referred to the sleep centre of the Ghent University Hospital, with a planned sample size of 500. Patients with suspected OSA are referred to the respiratory department, whereas the psychiatric department mainly offers care for patients with chronic insomnia and patients with unexplained chronic fatigue, who often complain of disturbed sleep or poor sleep quality. They are requested to complete the ESQ and other sleep questionnaires (ISI, FSS, ESS, PSQI) via the electronic patient portal before initial consultation. The same set of questionnaires is readministered prior to follow‐up consultations at 4 months and 1 year after treatment.

The results of these validation studies will be published. Data analysis will focus on descriptive statistics and construct validity, including structural validity and hypothesis testing, of the ESQ using a psychometric network approach (Christensen et al. 2020; Golino and Epskamp 2017). Convergent validity will be evaluated by examining how dimensions in the ESQ are related to those of other sleep questionnaires. Unstable items will be evaluated in conjunction with the findings from the cognitive interviews, informing the transition from ESQ prototype to a next version.

2.6. Completion

Based on findings from the validation studies, together with discussions within the core team and feedback from the Advisory Board, a release‐ready version (ESQ v1.0.0) will be developed from the current prototype. Item reduction will be informed by descriptive statistics, psychometric evaluation, insights from cognitive interviewing, and clinical relevance. At the component level (e.g., sleep latency), items will be scored as a weighted sum in which severity levels are weighted 1, 2, and 3 respectively, and bothersomeness is weighted 3, reflecting the unequal clinical contribution of each item to the overall symptom burden. Dimensions will be derived using a psychometric network approach, and dimension‐level scoring will be further developed by evaluating both expert‐informed and data‐driven candidate approaches, including simple sum scores and network loading‐weighted composite scores. In addition, a visual profile will be created displaying graphical scores for each sleep dimension, with colour gradients indicating the degree of severity. The released ESQ version is expected to be suitable for clinical practice and research. It will be made available as an open‐source instrument upon formal request by end users. Availability on digital platforms, for example, electronic patient systems is envisaged, but licensing and operational conditions are still under consideration.

It is important to recognize that the validation of PROMs is an ongoing process. The validity of these instruments is not a fixed attribute, but requires continuous re‐evaluation in light of feedback from end users and evolving clinical paradigms. Accordingly, any need for adaptation of the ESQ will be substantiated, optimisation will be planned, and new versions will be clearly labelled, beginning with v1.0.0—the version approved for release.

3. Future Directions

The ESQ is designed to provide a comprehensive record of sleep‐related symptoms and patient experiences, which will aid in formulating preliminary and differential diagnoses of sleep disorders. As the ESQ captures subjective data in considerable detail, it will support greater precision in sleep medicine. We expect that the ESQ could serve as an instrument for identifying and categorizing symptom‐based phenotypes (Rosales et al. 2025). As noted above, symptoms may be viewed either as components of a multisymptomatic disorder or as defining features of a distinct phenotype. In the latter case, when effective interventions are available, such features may represent treatable traits (Lisik et al. 2023; Pevernagie 2021). Ongoing analyses of treatment outcomes in the present study will clarify whether this potential can be realized. If so, this would further increase the clinical utility of the ESQ.

Future studies may expand the applicability and validation of the ESQ. First, the questionnaire needs to be evaluated in diagnostic categories beyond OSA and insomnia, such as circadian rhythm sleep–wake disorders, parasomnias, and hypersomnolence disorders. Second, the ESQ could be adapted for use in the general population for epidemiological or preventive purposes, or within specific groups of people (e.g., psychiatric populations, menopausal women, pregnant women, athletes, persons with disabilities). Interviews with these populations may help identify potentional areas for adaptation. Third, future studies should explore the functioning of a modular approach, enabling sections to be administered separately or in combinations. Finally, the linguistic and cultural equivalence of the translations with respect to the original English text will have to be checked. Planned steps to establish cross‐cultural validity include measurement invariance testing and construct validity evaluation across language groups, and conducting cognitive interviews in translated versions to culturally adapt items where needed.

4. Conclusions

Development of the ESQ was initiated within the EU‐funded Sleep Revolution project and is ongoing. The questionnaire was designed as a solution for the lack of comprehensive patient‐reported outcome measures in sleep medicine. Existing tools are limited in their ability to capture complex, overlapping phenotypes. The ESQ was designed through a multi‐phase process involving literature review, expert and patient input, and iterative framework development. The current version includes 119 items across nine sections, assessing symptom severity, frequency, and bothersomeness through Likert scales. It has been implemented on the SleepWell digital platform for multicenter research in different languages. Validation studies include cognitive interviews in patients with different sleep disorders and psychometric testing in OSA and insomnia cohorts. The ESQ will be licensed for public use in research and clinical practice. Future directions involve expanding validation to other sleep disorders, adapting the ESQ for epidemiological use, refining translations, and optimizing visualization for clinical decision‐making.

Author Contributions

Piet‐Heijn van Mechelen: conceptualization, methodology, writing – review and editing, investigation. Marie De Bruecker: conceptualization, writing – original draft, methodology, writing – review and editing, supervision, investigation, project administration. Elke Veirman: conceptualization, methodology, writing – review and editing, supervision, data curation, investigation, writing – original draft. Inger L. Abma: conceptualization, methodology, writing – review and editing, investigation. Anna Sigridur. Islind: conceptualization, methodology, writing – review and editing, funding acquisition, data curation, writing – original draft, investigation, project administration, software. Katrien Hertegonne: conceptualization, methodology, writing – review and editing, supervision, investigation, writing – original draft. Kamilla Rún Jóhannsdóttir: conceptualization, methodology, writing – review and editing, investigation. Fré A. Bauters: conceptualization, methodology, writing – review and editing, supervision, investigation, writing – original draft. Dimitri M. L. Van Ryckeghem: conceptualization, methodology, writing – review and editing, supervision, investigation, writing – original draft. Geert Crombez: conceptualization, methodology, writing – review and editing, supervision, investigation, writing – original draft. Ludger Grote: conceptualization, methodology, writing – review and editing, project administration, funding acquisition, investigation. Kristín Anna Ólafsdóttir: funding acquisition, conceptualization, methodology, writing – review and editing, resources, project administration. Jan Hedner: conceptualization, methodology, writing – review and editing, investigation. An Mariman: conceptualization, methodology, writing – review and editing, funding acquisition, investigation, supervision, writing – original draft. Reijo Sund: conceptualization, methodology, writing – review and editing, investigation. Gert Jan Lammers: conceptualization, methodology, writing – review and editing, investigation. Sebastiaan Overeem: conceptualization, methodology, writing – review and editing, investigation. Dieter Riemann: conceptualization, methodology, writing – review and editing, investigation. Dirk A. Pevernagie: conceptualization, methodology, writing – original draft, writing – review and editing, supervision, funding acquisition, investigation. Erna Sif Arnardottir: conceptualization, methodology, writing – review and editing, writing – original draft, funding acquisition, investigation, project administration. Walter T. McNicholas: conceptualization, methodology, writing – review and editing, investigation.

Funding

This work is supported by the European Union's Horizon 2020 Research and Innovation Programme under Grant 965417 (Sleep Revolution). Ludger Grote was funded by the Swedish Heart and Lung foundation (20240848) and the Swedish governmental funding of clinical research (ALF) (ALFGBG1006211). An Mariman received a grant from the Special Research Fund of Ghent University to support the Sleep Revolution project (BOFBAF2024071501).

Conflicts of Interest

Geert Crombez discloses lecture fees from SA Grünenthal. Erna Sif Arnardottir discloses lecture fees from Nox Medical, ResMed, Jazz Pharmaceuticals, Linde Healthcare, Wink Sleep, Apnimed and Vistor. She is a previous member of a Philips Sleep Medicine & Innovation Medical Advisory Board and Lille Medical Advisory Board and is currently on a Sleep Cycle Data Monitoring Committee. Ludger Grote reports lecturing activities for Resmed, Philips, Itamar, Astra Zeneca and Lundbeck. He is a member of the advisory board for ONERA and he is a shareholder of a company with a licensed patent on pharmacological treatment in OSA. Sebastiaan Overeem received an unrestricted research grant from Takeda and participated in advisory boards for Jazz Pharmaceuticals, Takeda, Bioprojet and Abbvie, all unrelated to the present work.

Supporting information

Data S1: jsr70401‐sup‐0001‐Supinfo1.pdf.

JSR-35-e70401-s001.pdf (74.4KB, pdf)

Data S2: jsr70401‐sup‐0002‐Supinfo2.pdf.

JSR-35-e70401-s002.pdf (532.9KB, pdf)

Acknowledgements

The authors want to thank the researchers of the Sleep Revolution consortium, the sleep practitioners and patients that filled out the surveys, the patients who participated in the cognitive interviews, as well as all the patients who filled out the ESQ and other sleep questionnaires. We also thank Mrs. Marijke IJff, delegate from the “Apneuvereniging” and previous member of the Advisory Board, who elected not to contribute to the paper. We thankfully acknowledge the work of Helga Björt Lilliendahl, bachelor student at the Department of Computer Science, Reykjavik University, Reykjavik, Iceland. She contributed to the integration of the ESQ into the Sleep Well platform. ChatGPT was used in order to improve readability and to ensure linguistic correctness. AI was not used for content generation. All AI‐assisted output was carefully reviewed, verified, further adapted and approved by the authors, who take full responsibility for the final content.

Pevernagie, D. A. , De Bruecker M., Veirman E., et al. 2026. “The Development of the European Sleep Questionnaire A New Patient‐Reported Outcome Measure.” Journal of Sleep Research 35, no. 5: e70401. 10.1111/jsr.70401.

Dirk A. Pevernagie and Marie De Bruecker contributed equally to this work and are co‐corresponding authors.

Dirk A. Pevernagie and Marie De Bruecker share first authorship.

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Data S1: jsr70401‐sup‐0001‐Supinfo1.pdf.

JSR-35-e70401-s001.pdf (74.4KB, pdf)

Data S2: jsr70401‐sup‐0002‐Supinfo2.pdf.

JSR-35-e70401-s002.pdf (532.9KB, pdf)

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

Articles from Journal of Sleep Research are provided here courtesy of Wiley

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