How chronic pain is defined matters: Prevalence estimates and health-related quality of life under alternative definitions

Abstract

Background

Chronic pain is a leading cause of long-term disability, yet prevalence estimates vary widely due to differences in operational definitions. Although a 3-month duration criterion is commonly used, it may not adequately reflect the functional burden of chronic pain. This study compared prevalence estimates derived from alternative chronic pain definitions and evaluated which best identify individuals with impaired health-related quality of life (HRQoL).

Methods

Data were drawn from a population-based sample of adults (n = 5557). Pain was assessed using the Brief Pain Inventory, and HRQoL was measured with the Short Form 12 Health Survey (SF-12v2). Six definitions were examined: duration-only (≥3 months), pain pattern (constant or daily intermittent), pain severity thresholds (≥3 and ≥4), and pain interference thresholds (≥3 and ≥4).

Results

Prevalence estimates varied substantially by definition, ranging from 40.1% using duration alone to 12.0% using pain interference ≥4. Increasingly restrictive definitions were associated with progressively lower physical and mental health scores. Effect sizes for physical health impairment increased from Cohen’s d = 0.81 for the duration-only definition to 1.68 for the most restrictive interference-based definition. Definitions incorporating pain interference most clearly distinguished individuals with reduced HRQoL.

Conclusions

The operational definition of chronic pain strongly influences both prevalence estimates and identification of clinically meaningful impairment. Definitions incorporating functional impact more accurately identify high-burden chronic pain than duration alone, supporting the integration of temporal and functional dimensions in standardised definitions.

Keywords

chronic pain health-related quality of life epidemiology pain characteristics

Introduction

Chronic pain is a complex condition, a major global health concern and one of the leading causes of impaired quality of life and long-term disability.^1,2 However, its reported prevalence varies considerably across studies due to differences in definitions, measurement instruments, study populations, and methodological approaches, underscoring the need for a more standardised criteria in epidemiological research.^3–5

The International Association for the Study of Pain (IASP) and the International Classification of Diseases, 11th Revision (ICD-11), define chronic pain as persistent or recurrent pain lasting longer than 3 months and associated with significant emotional distress and/or functional disability.^2,6 However, while this definition provides an important conceptual framework, it does not specify standardised operational criteria for key dimensions such as pain severity, temporal pattern, or functional impact. Consequently, its operationalisation varies considerably across studies, contributing to inconsistencies in prevalence estimates and limiting comparability across epidemiological research.^1–3

As a result of this heterogeneity, reported prevalence estimates of chronic pain vary widely across epidemiological studies, largely due to historical inconsistencies in operational definitions. While some studies define chronic pain solely by duration (e.g. pain lasting ≥3 months), others additionally require pain on most days or daily pain, whereas still others incorporate minimum severity or interference thresholds. Multiple reviews and methodological discussions have demonstrated that this definitional inconsistency has produced markedly divergent prevalence estimates, highlighting the 3-month duration criterion as the core operational definition in population-based research.^1,7–9

A systematic review of 86 population-based studies identified chronic pain prevalence estimates ranging from 8.7% to 64.4%, highlighting how methodological variability undermines comparability across studies.³ Similarly, Fayaz et al. (2016)⁴ reported a pooled prevalence of 43.5% for chronic pain defined by a duration of 3 months or longer, ranging from 35.0% to 51.3% across studies. More recent analyses confirm that differences in operational definitions, particularly the inclusion or exclusion of pain pattern, severity, or interference thresholds, continue to influence prevalence estimates.^5,7 Despite these differences, the 3-month duration criterion remains the most widely used operational definition in epidemiological research. However, reliance on duration alone may be insufficient to capture the burden of chronic pain. Several authors have therefore emphasised the importance of incorporating measures of pain interference, such as the Brief Pain Inventory (BPI), to improve epidemiological precision and enhance clinical relevance.^1,10,11 Accordingly, recent reviews and methodological discussions consistently call for greater standardisation of chronic pain definitions including uniform time frames, assessment of pain severity and interference, and consideration of functional impact and quality of life.^1,7–9,12 Instruments such as the BPI allow for systematic assessment of pain-related interference with daily activities and have been shown to more consistently identify individuals with clinically meaningful impairment than duration-based definitions alone.¹ Because the public health and clinical relevance of chronic pain lie in its impact on functioning and well-being, the ability of a definition to identify individuals with impaired HRQoL represents a meaningful criterion for evaluating alternative operational definitions.¹³

The present analysis draws on data from a large population-based study of adults (18–80 years), enabling direct comparison of alternative chronic pain definitions within the same population. Addressing a key gap in the literature, this study systematically compares commonly used chronic pain definitions and evaluates their ability to identify individuals with impaired HRQoL. Despite appearing conceptually subtle, commonly used differences in the operational definition of chronic pain may result in substantial divergence in both prevalence estimates and the identification of individuals with clinically meaningful impairment. The aim of this study was to compare prevalence estimates derived from different chronic pain definitions and to determine which definition most effectively captures chronic pain associated with meaningful interference in daily life and reduced HRQoL.

Methods

Sample and data collection procedures

Data were collected through a web-based platform provided by a service contractor, Maskina (https://maskina.is/en/maskinan/fyrirtaekid/), using a national panel recruited from the National Population Register of Iceland. At the time of data collection, the panel comprised approximately 20,000 members. Recruitment procedures use demographic quotas to reflect the age, sex, and regional composition of the Icelandic adult population and therefore do not rely on voluntary self-selection. From Maskina’s national panel, a sample of 12,400 individuals aged 18–80 years were randomly selected and invited to participate by email, which included detailed information about the study. To ensure a proportional representation of men and women across age groups and regions of the country, the sample was stratified by sex, age, and place of residence. The study protocol was approved by the Icelandic National Bioethics Committee (VSN-19-096). In accordance with the research ethics guidelines of the Icelandic National Bioethics Committee, participants were not required to answer all questions. Informed consent was implied by participants’ completion of the questionnaire.

In January 2021, the population of Iceland was 358,298 (47.7% women), of which 265,042 were aged 18–80 years (49.0% women). About 70% of the population lived in municipalities with more than 15,000 residents, and 64.1% resided in the capital area.¹⁴

Procedure

Participants received an email invitation containing information about the study purpose, confidentiality, voluntary participation, and a secure hyperlink to the online questionnaire. After accessing the survey platform, they were presented with study information and informed that they were free to skip individual questions or discontinue participation at any time. Participants could also pause completion and return later using the survey link provided in the invitation email. Completion of the questionnaire was taken to indicate informed consent.

The questionnaire was presented in a fixed order and included sociodemographic items, general health and health-related quality of life measures, sleep and lifestyle questions, health conditions and related experiences, pain-related measures, and background variables. Given the breadth of the survey, completion typically required more than 15 min. No monetary incentives were provided.

Instruments

The survey included questionnaires assessing pain and HRQoL, along with items on physical activity, sleep, height and weight, and sociodemographic characteristics. HRQoL was assessed using the SF-12v2, a widely used validated instrument. Items assessing physical activity and sleep were adapted from questions used in a national Icelandic health and well-being survey conducted by the Icelandic Directorate of Health. These variables were included as descriptive covariates rather than primary outcome measures.

Participants reported how often and for how long they engaged in physical exercise (e.g. swimming, walking, and cycling). Frequency options ranged from never to three times per week or more, and duration categories ranged from less than 15 min to more than 60 min. Using combined information on frequency and duration, physical exercise was recoded into four weekly activity levels: no exercise or less than 15 min per week, little (15–45 min), moderate (45–90 min), and high (more than 90 min per week). Sleep quality was assessed using four items covering continuous sleep, waking up rested, difficulty falling asleep, and waking up during the night, referring to the past 4 weeks. Response options ranged from never to every night. Based on these responses, sleep problems were classified as none, moderate, or serious. Serious problems were defined by poor ratings on positive items (never/seldom) combined with frequent difficulties on negative items (often/always). No problems reflected the opposite trend, while mixed or intermediate responses were categorised as moderate sleep problems. Participants’ self-reported height and weight were used to calculate body mass index (BMI), which was subsequently categorised as normal weight (<25), overweight (25–29.9), or obesity (≥30).

Sociodemographic characteristics

The sociodemographic data collected were sex, age, marital status, education, satisfaction with household income, and occupational status (Employed, Disabled, Other, (e.g. Other = Unemployed/Retired/I am studying)).

Pain prevalence, characteristics of pain, and interference with daily life

The Icelandic version of the Brief Pain Inventory (BPI) was used to evaluate pain experience, severity, and interference with daily life.^15,16 Participants were asked if they had experienced pain (other than minor headaches, sprains, or toothaches) the previous week and, if so, for how long the pain had lasted (years, months, weeks). Participants were also asked about the cause of pain and to indicate on a body map where they felt pain.

The BPI contains three questions regarding pain severity during the past 24 h (worst, least, and average pain) and pain at present on a scale from 0 to 10, where 0 indicates no pain and 10 is the worst pain imaginable. Interference with life is evaluated by questions on the impact of pain on seven aspects of daily life – mood, walking ability, work, social activity, sleep, and life enjoyment – on a 0 to 10 scale anchored with ‘does not interfere’ (0) and ‘completely interferes’ (10).¹⁶ By using separate means of the four severity items and the seven interference items, two composite scores, the Pain Severity Index and the Pain Interference Index, are calculated.¹⁷ The BPI has been translated into Icelandic and validated in a general population sample of adults experiencing pain of various origins. It has been found to be both reliable and valid.^15,18 Thresholds of ≥3 and ≥4 were applied for both severity and interference to distinguish mild from moderate-to-severe pain impact.

Respondents were asked to answer a question about the pattern of pain, classified as constant (pain all the time), daily intermittent (daily pain with one to a few hours break during the day), frequent intermittent (pain most days but pain-free days in between), and periodic (pain-free periods for days or weeks but pain episodes in between).

Operational definitions of chronic pain

Six alternative operational definitions of chronic pain were examined in the present study. First, chronic pain was defined as pain lasting ≥3 months, consistent with commonly used epidemiological definitions and international frameworks.^2,6,19 Second, chronic pain was defined as pain lasting ≥3 months combined with constant or daily intermittent pain, reflecting more persistent pain frequency.²⁰ Third and fourth, chronic pain was defined as pain lasting ≥3 months combined with a Brief Pain Inventory (BPI) Pain Severity Index score of ≥3 or ≥4, respectively. Fifth and sixth, chronic pain was defined as pain lasting ≥3 months combined with a BPI Pain Interference Index score of ≥3 or ≥4, respectively. Severity and interference thresholds were examined because multidimensional pain measures may better identify clinically meaningful chronic pain burden than duration alone.^5,7,10,11

Health-related quality of life (HRQoL)

The Short Form 12 Health Survey version 2 (SF-12v2), is a 12-item self-rating questionnaire to assess HRQoL and perceived health status in various health conditions, measures eight domains of physical and mental health from which physical component scale (PCS) and mental component scale (MCS) scores are calculated.²¹ Each of the components is scored on a 0–100 scale, with a mean of 50, where higher scores indicate better health.^21,22 The instrument’s reliability and validity have been tested and confirmed in relation to public health^21,23,24 and chronic non-cancer pain.²²

Statistical analyses

Data were analysed using SPSS for Windows (version 28.0) and Stata. Descriptive statistics were presented as means with standard deviations for continuous variables and as frequencies with percentages for categorical variables. Point prevalence was expressed as percentages with 95% confidence intervals (CI). Differences in categorical variables between participants with and without chronic pain were assessed using chi-square tests, while independent-samples t-tests were used for comparisons of continuous variables.

Results

Characteristics of the study population

The study sample comprised 5557 participants aged 18–80 years (44.8% response rate), of whom 57.1% were women. The mean age was 54.8 years (SD 13.7). Sociodemographic and lifestyle characteristics of the study population, stratified by chronic pain status (pain duration ≥3 months), are presented in Table 1.

Table 1.

Sociodemographic and lifestyle characteristics of the study population, by chronic pain status.

Variable	Total sample (N = 5557)		Without chronic pain		With chronic pain		p-value
Variable	N	%	n	%	n	%
Sex							<0.001^a
Men	2365	42.6	1502	45.2	863	38.9
Women	3173	57.1	1818	54.8	1355	61.1
Missing	19	0.3
Age							0.037^b
Mean (sd/n)	5557	54.8 (13.7)	3331	54.5 (14.2)	2226	55.3 (13.0)
Age							<0.001^a
18–34 y	547	10.0	371	11.4	176	8.0
35–49 y	1360	24.9	813	24.9	547	24.9
50–64 y	2023	37.1	1139	34.9	884	40.2
65–80 y	1527	28.0	936	28.7	591	26.9
Marital status							0.929^a
Married/cohabit	4386	79.2	2628	79.3	1758	79.2
Single/divorced/widowed	1151	20.8	688	20.7	463	20.8
Education							0.006^a
Primary	779	15.1	420	13.9	359	16.8
Secondary	1939	37.6	1127	37.3	812	37.9
Tertiary	2441	47.3	1472	48.8	969	45.3
Household income							<0.001^a
Satisfactory	3956	77.5	2448	82.0	1508	71.0
Unsatisfactory	1151	22.5	536	18.0	615	29.0
Occupational status							<0.001^a
Employed	3531	68.4	2159	71.5	1372	63.9
Disabled	309	6.0	90	3.0	219	10.2
Other	1324	25.6	769	25.5	555	25.9
Physical activity							<0.001^a
Low	1897	35.4	1016	32.3	881	39.7
Moderate	1320	24.6	797	25.3	523	23.5
High	2149	40.0	1332	42.4	817	36.8
Sleep quality							<0.001^a
No sleep problems	2273	42.7	1617	51.8	656	29.8
Moderate sleep problems	1613	30.3	912	29.2	701	31.9
Serious sleep problems	1434	27.0	593	19.0	841	38.3
BMI							<0.001^b
Mean (sd/n)	4556	28.7 (5.5)	2645	27.9 (5.1)	1911	29.7 (5.8)
BMI
Mean (sd/n)							<0.001^a
<25	1186	26.0	804	30.4	382	20.0
25–30	1799	39.5	1065	40.3	734	38.4
>30	1571	34.5	776	29.3	795	41.6

^aChi-square test.

^bStudents t-test.

Half of the participants (50.3%) responded that they had experienced pain during the previous week, and 40.1% had chronic pain (≥3 months). While the mean duration of chronic pain was 13.6 years, the data was heavily skewed; the median duration was 7 years (Q1 = 2, Q3 = 20). Participants with chronic pain were more likely to be women and to belong to the middle-aged group (50–64 years). The majority of those with chronic pain reported experiencing constant or daily pain (64.6%), and 35.4% had frequent or periodic pain. Chronic pain prevalence was inversely associated with educational level and household income; individuals reporting unsatisfactory household income were substantially more likely to report chronic pain than those with satisfactory income. Participants with chronic pain also had higher mean body mass index and a higher prevalence of obesity compared with those without chronic pain. Disability status, low physical activity, and moderate or serious sleep problems were more common among individuals with chronic pain, whereas marital status did not differ between groups.

Prevalence of chronic pain according to alternative definitions

The estimated prevalence of chronic pain varied markedly depending on the operational definition applied (Figure 1). When chronic pain was defined solely by pain duration of 3 months or longer, 40.1% of the population met the criterion. Introducing additional criteria progressively reduced prevalence estimates.

Figure 1.

Prevalence of chronic pain under different definitions.

Restricting the definition to constant or daily pain reduced the prevalence to 26.5%. Applying thresholds for pain severity resulted in prevalences of 23.8% for severity ≥3 and 16.5% for severity ≥4. Similarly, incorporating pain interference criteria identified smaller subgroups, with prevalences of 16.4% for interference ≥3 and 12.0% for interference ≥4. When the different chronic pain definitions were stratified by sex, prevalence was consistently higher among women than men across all definitions.

Health-related quality of life by chronic pain definition

PCS declined progressively as chronic pain definitions became more restrictive (Table 2). Participants meeting only the duration-based criterion (≥3 months) exhibited a moderate reduction in PCS compared with those without chronic pain. In contrast, definitions incorporating pain pattern, severity, or interference were associated with substantially larger reductions in PCS.

Table 2.

Physical and mental health-related quality of life (SF-12 PCS and MCS scores) among participants with and without chronic pain under alternative operational definitions.

	No chronic pain	Chronic pain	p-value^a	Cohen’s d	95% CI
PCS physical component score
Pain ≥3 months	51.5 (8.7/3199)	43.6 (11.0/2221)	<0.001	0.810	0.754	0.866
Pattern constant	51.2 (8.7/3952)	40.5 (10.9/1468)	<0.001	1.142	1.078	1.205
+Daily intermittent
Pain severity ≥3	51.0 (8.9/4104)	40.0 (10.8/1316)	<0.001	1.173	1.107	1.239
Pain severity ≥4	50.4 (9.2/4506)	37.9 (10.4/914)	<0.001	1.331	1.256	1.407
Pain interference ≥3	50.6 (8.9/4513)	36.7 (9.9/907)	<0.001	1.528	1.451	1.605
Pain interference ≥4	50.2 (9.1/4757)	34.8 (9.6/663)	<0.001	1.679	1.592	1.766
MCS mental component score
Pain ≥3 months	50.1 (9.2/3202)	47.0 (10.4/2223)	<0.001	0.316	0.261	0.370
Pattern constant	49.9 (9.3/3956)	46.1 (10.5/1469)	<0.001	0.396	0.336	0.456
+Daily intermittent
Pain severity ≥3	49.9 (9.3/4107)	45.6 (10.7/1318)	<0.001	0.448	0.385	0.511
Pain severity ≥4	49.6 (9.4/4509)	45.0 (10.8/916)	<0.001	0.477	0.406	0.549
Pain interference ≥3	49.8 (9.3/4516)	43.9 (10.7/909)	<0.001	0.623	0.551	0.696
Pain interference ≥4	49.7 (9.4/4760)	42.7 (10.7/665)	<0.001	0.738	0.655	0.820

^aStudent´s t-test.

The largest impairments in physical health were observed among participants meeting definitions that included pain interference thresholds, particularly interference ≥4. Effect size estimates confirmed a clear gradient, with Cohen’s d increasing from 0.81 for the duration-only definition to 1.68 for the most restrictive interference-based definition (Table 2), indicating large and clinically meaningful differences in physical functioning.

Global comparisons of the differences in PCS across chronic pain definitions supported the observed monotonic decline in physical health with increasing definition strictness.

MCS also differed across chronic pain definitions, although the magnitude of differences was smaller than for physical health (Table 2). Participants classified as having chronic pain based solely on duration showed modest reductions in Mental Component Scores (MCS). Increasingly restrictive definitions incorporating pain severity and interference were associated with progressively lower MCS values.

Effect sizes for mental health outcomes ranged from small to moderate, with Cohen’s d increasing from 0.32 for the duration-only definition to 0.74 for pain interference ≥4 (Table 2). As with physical health, global differences in MCS across chronic pain definitions indicated a gradual increase in psychological burden with stricter chronic pain criteria.

Across both physical and mental health outcomes, stricter chronic pain definitions consistently identified subgroups with greater impairment in health-related quality of life. Definitions incorporating pain severity and in particular, pain interference with daily life were most effective in distinguishing individuals with clinically meaningful reductions in HRQoL, whereas reliance on duration alone captured a broader and more heterogeneous group with comparatively smaller impairments.

Discussion

This population-based study demonstrates that both the estimated prevalence of chronic pain and the identification of individuals with clinically meaningful impairment vary substantially depending on how chronic pain is operationally defined. Reliance on pain duration alone identifies a broad and heterogeneous segment of the population, whereas definitions incorporating pain severity and, most notably, pain interference with daily life more consistently identify individuals with pronounced reductions in health-related quality of life (HRQoL).

When chronic pain was defined solely by duration of 3 months or longer, approximately 40% of the population met the criterion. However, when introducing additional criteria, the prevalence estimates progressively reduced. Restricting the definition to individuals with constant or daily pain reduced prevalence to approximately one quarter of the population, while applying thresholds for pain severity or pain interference identified substantially smaller subgroups. These findings align with prior studies demonstrating wide variability in prevalence estimates depending on operational choices and confirm that duration-based definitions capture a large group with highly variable pain burden.^5,7,9

Clinical evidence indicates that persistent pain patterns are associated with higher pain severity than intermittent patterns, underscoring the importance of incorporating both temporal characteristics and severity into chronic pain definitions.²⁰ Consistent with this, recent studies incorporating pattern or frequency, severity, or functional impact yield markedly lower prevalence estimates. For example, Shibata et al. (2025)⁵ reported prevalence ranging from approximately 13% under strict criteria to nearly 48% when duration alone was used, and Daoust et al. (2025)⁷ demonstrated similar variability (17–45%) depending on definition. Together, these studies confirm that operational choices substantially influence who is classified as having chronic pain.

The observed sociodemographic gradients, including higher prevalence of chronic pain among women, middle-aged individuals, and those with lower education or household income, are consistent with established epidemiological patterns.^1,4,25,26 Associations with higher body mass index, lower physical activity, sleep problems, and disability further support the external validity of the findings. Importantly, these gradients were evident across alternative definitions, suggesting that while prevalence estimates vary with definition, underlying social and health inequalities in chronic pain burden remain robust.

A key contribution of this study lies in its systematic examination of HRQoL across alternative chronic pain definitions. Physical health (PCS) declined monotonically as definitions became more restrictive, with the largest impairments observed among individuals meeting criteria that included pain interference thresholds. Effect size estimates confirmed that definitions incorporating interference identified groups with large and clinically meaningful reductions in physical functioning, whereas duration-only definitions were associated with more moderate impairments. Mental health (MCS) outcomes followed a similar trend, though less pronounced, gradient. These findings align with previous work emphasising the biopsychosocial nature of chronic pain and the importance of lived experience and functional impact in distinguishing high-burden pain conditions.^1,13,27

These findings are also consistent with earlier work by Michael Von Korff²⁸ and colleagues, who proposed that chronic pain is more meaningfully characterised by graded measures of pain severity and pain-related disability than by duration alone. The Graded Chronic Pain Scale (GCPS) and its revised version, distinguishing mild, bothersome, and high-impact chronic pain, emphasise the importance of functional consequences when identifying clinically significant pain states. Relatedly, recent work has suggested that pain bothersomeness may provide an additional patient-centred indicator of biopsychosocial burden and quality of life beyond pain severity alone.²⁹ Our findings similarly indicate that definitions incorporating pain interference more effectively identify individuals with substantial reductions in physical and mental health-related quality of life.

From a public health perspective, these findings have important implications. Reliance on duration alone identifies a broader segment of the population than definitions that incorporate pain severity and functional impact, suggesting that surveillance systems based exclusively on duration may overestimate clinically meaningful chronic pain burden. While the 3-month duration criterion remains an important foundation for defining chronic pain, the present findings suggest that duration alone may not adequately distinguish clinically meaningful cases from a more heterogeneous group of individuals with long-duration pain states. Definitions incorporating pain severity, and particularly pain interference with daily life, more consistently identify subgroups with pronounced reductions in HRQoL, thereby enhancing relevance for healthcare planning and resource allocation.

Strengths and limitations

The strengths of this study include its large population-based sample, acceptable response rate, and use of validated instruments for assessing pain severity, pain interference, and health-related quality of life. The ability to directly compare alternative chronic pain definitions within the same population represents a particular methodological advantage. Several limitations should be acknowledged. The cross-sectional design precludes causal inference, and all measures were self-reported, which may introduce reporting bias. Although the study sample was broadly representative of the adult general population with respect to age and sex, non-response bias cannot be excluded, and the findings may not be fully generalisable to populations with different healthcare systems or sociodemographic contexts. In addition, while commonly used thresholds for pain severity and interference were applied, no universally accepted cut-offs exist, and alternative operationalisations may yield different prevalence estimates. Although smoking and alcohol use were assessed in the broader survey, these variables were not included in the present analysis because the primary focus was on definitional differences in chronic pain and HRQoL. Future studies may examine their contribution in greater detail. Cultural norms, language, coping styles, and willingness to report pain may vary across countries and influence self-reported prevalence estimates. Consequently, the absolute estimates observed in this Icelandic sample may not be directly transferable to other settings. However, the broader methodological implication that multidimensional chronic pain definitions may better identify clinically meaningful burden than duration alone is likely to extend beyond the present context.

Conclusion

In conclusion, this study provides empirical evidence that the choice of chronic pain definition has a substantial impact on prevalence estimates and on the identification of individuals with clinically meaningful impairment. Definitions based only on duration may fail to capture the subgroup experiencing clinically meaningful interference and reduced HRQoL. In contrast, definitions incorporating pain severity and functional impact more effectively capture clinically relevant chronic pain. These results support ongoing calls for greater standardisation of chronic pain definitions that integrate both temporal and functional dimensions, thereby improving comparability across studies and enhancing the relevance of epidemiological estimates for clinical practice and public health planning.

Footnotes

Author note

Any other identifying information related to the authors and/or their institutions, funders, approval committees, etc, that might compromise anonymity: The study is done in Iceland, and Iceland is mentioned several times, but no identifying information related to the authors or their institutions is provided.

Acknowledgements

We thank all those who took part in the study. We also wish to thank the University of Akureyri Research Fund and the Icelandic Public Health Fund for supporting the study.

ORCID iDs

Thorbjorg Jonsdottir

E. Halapi

H. Skuladottir

G.K. Oskarsson

Ethical considerations

The study protocol was approved by the Icelandic National Bioethics Committee (VSN-19-096). Informed consent was implied by participants’ completion of the questionnaire.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The ICEPAIN-study is funded by the University of Akureyri Research Fund and the Icelandic Public Health Fund (Lýðheilsusjóður).

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data Availability Statement

Complete datasets, generated or analysed during this study, are not shared due to confidentiality.*

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