Reliability and cross-group equivalence of the 8-item version of the Patient Health Questionnaire (PHQ-8) to screen for depression in adults with and without chronic pain: a nationally representative U.S. population study
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Background
The 8-item Patient Health Questionnaire (PHQ-8) is the most widely implemented clinical depression screener in the world and is increasingly influential in population surveillance of unmet mental health needs. However, in the context of chronic pain (CP), depression screening could be challenging due to overlapping somatic symptoms. Concerns have been raised that inaccurate attribution of CP symptoms to depression could lead to overestimation of depressive symptom severity or even artifactual inflation of depression prevalence estimates. Results of several small, non-representative studies are inconclusive; suitability of the PHQ-8 to screen for depression in those with CP remains unclear. We aimed to determine the reliability and cross-group equivalence of PHQ-8 in adults with and without CP.
Methods
This cross-sectional observational survey study used representative data from the 2019 National Health Interview Survey. Descriptive analyses, confirmatory factor analyses, tests of measurement invariance and cross-group equivalence, and item response theory analyses were completed.
Findings
The final sample contained 30,983 respondents. Measurement invariance and cross-group equivalence was observed at the configural, metric, and scalar levels. Prevalence of clinically significant depressive symptoms was 3.5% in adults without CP, 20.1% in those with CP, and 34.8% in high-impact chronic pain (HICP). No evidence consistent with overestimation of depression prevalence or severity in the contexts of CP or HICP was observed.
Interpretation
The PHQ-8 measures depressive symptoms equivalently in the context of chronic pain, supporting the continued use of PHQ-8 to screen for depression and to support epidemiological surveillance in adults with and without CP. Empirical evidence suggests that CP-associated disparities are very unlikely to result from measurement issues more likely to be reflective of true differences in prevalence and severity of depressive symptoms in this high-risk group.
Funding
Comprehensive Center for Pain & Addiction, University of Arizona Health Sciences.
RESEARCH IN CONTEXT
Evidence before this study
Depression screening tools have been implemented into general health settings worldwide; today, most cases of major depression are identified and addressed in primary or urgent care settings. Chronic pain frequently co-occurs with depression, and chronic pain may be especially prevalent in settings most likely to implement depression screening is part of routine clinical practice.
However, screening for depression among those with chronic pain could be complicated by overlapping somatic symptoms that are part of diagnostic criteria for depression and often occur with chronic pain—e.g. sleep disturbance, fatigue, appetite changes, and psychomotor slowing. Furthermore, concerns about criterion contamination are not exclusive to somatic symptoms: chronic pain is also associated with cognitive and affective symptoms that similarly overlap with diagnostic criteria for depression. Systematic bias in depression screening among those with CP could lead to overestimation of depressive symptom severity in clinical settings or artificial inflation of depression prevalence among those living with chronic pain.
Several studies have examined small, non-representative patient samples; findings are inconclusive. The reliability and equivalence of standard depression screening tools to measure depressive symptoms in the context of chronic pain has remained persistently unclear.
Added value of this study
The PHQ-8 is the most widely implemented depression screening tool in the world, and it holds an increasingly influential role in epidemiological surveillance of unmet mental health needs. If PHQ-8 functions differently in those with chronic pain, clinical decisions, scientific studies, and even epidemiological surveillance tools could be systematically biased. This representative cross-sectional survey study of 30,983 U.S. adults is the first to determine the reliability and cross-group equivalence of the PHQ-8 in those with and without CP: addressing a persistent knowledge gap with important implications for clinical practice, scientific research, and global public health. Cross-group equivalence and measurement invariance were observed between those with and without CP at the configural, metric, and scalar levels. These results provide clear evidence that PHQ-8 is reliable, consistent, and functions equivalently in adults with and without CP.
Implications of all the available evidence
Empirical evidence did not support with the hypothesis that measurement artifacts contribute to elevated depressive symptoms in those with CP. Findings should enhance confidence among clinicians and researchers that PHQ-8 is appropriate to screen for depressive symptoms in the clinical context of CP and that the interpretation of screening results is straightforward. Findings underscore the verifiable existence of profound mental health disparities experienced by U.S. adults with CP, including increased prevalence of depression, increased severity of depressive symptoms, reduced likelihood that depressive symptoms will be identified, and reduced likelihood of receiving needed mental health support.
