Reliability and equivalence of the 8-item version of the Patient Health Questionnaire (PHQ-8) to screen for depressive symptoms in adults with chronic pain: A representative U.S. population study

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 complicated by overlapping symptoms. 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 small, non-representative studies are heterogenous; suitability of the PHQ-8 to screen for depression in those with CP remains unclear. We aimed to determine the reliability and equivalence of PHQ-8 in adults with and without CP.

Methods

This cross-sectional observational population study used representative data from the 2019 National Health Interview Survey. Descriptive statistics and visualizations were generated; reliability, cross-group equivalence and measurement invariance were assessed.

Findings

The final sample contained 30,983 U.S. adults. Prevalence of clinically significant depressive symptoms was 3.5% in those without CP, 20.1% in those with CP, and 34.8% in those with high-impact chronic pain (HICP). Reliability, measurement invariance and cross-group equivalence were observed at the configural, metric, and scalar levels. No evidence consistent with overestimation of depression prevalence or severity in the contexts of CP or HICP was observed.

Interpretation

The PHQ-8 is reliable and measures depressive symptoms equivalently in the context of CP, supporting the continued use of PHQ-8 to screen for depression in clinical and research settings and in population surveillance of adults with and without CP. CP was associated with five times higher prevalence of clinically significant depressive symptoms; findings suggest this reflects true cross-group differences in prevalence and severity of depressive symptoms and is unlikely to result from measurement issues.

Funding

This work was funded in part by the Comprehensive Center for Pain & Addiction, University of Arizona, and by NIH K23HD104934.

RESEARCH IN CONTEXT

Evidence before this study

PubMed and Google Scholar were searched without time constraints using Key Terms: “depress∗” and (“chronic pain” OR “fibromyalgia” OR “migraine” OR “headache” OR musculoskeletal” OR “arthritis”) and “assess∗” OR (“measur∗” OR “evaluat∗ OR “screen*”). Additional studies were identified from the reference lists of the resulting papers. Though many studies have examined assessment of depression in the context of chronic pain, nearly all appear to be limited by non-representative samples, failure to incorporate non-focal comparison groups, or both. As a result, the reliability and equivalence of standard depression screening tools to measure depressive symptoms in the clinical 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: it is frequently used in clinical practice, scientific research, and is becoming increasingly influential in the global surveillance of unmet mental health needs. Systematic bias of depression screening in the context of chronic pain is an important concern. If PHQ-8 functions differently in those with chronic pain, clinical decisions, scientific studies, and even epidemiological estimates could be substantially biased. To our knowledge, this cross-sectional survey study of 30,983 U.S. adults is the first to use representative population data comparing those with and without chronic pain to determine the reliability and cross-group equivalence of the PHQ-8: addressing a persistent knowledge gap with important implications for clinical practice, scientific research, and global public health. The PHQ-8 was demonstrated to be reliable in adults with chronic pain. Cross-group equivalence and measurement invariance were observed between those with and without chronic pain at the configural, metric, and scalar levels. These results provide compelling evidence that PHQ-8 is reliable and functions equivalently to screen for depression in adults with and without chronic pain.

Implications of all the available evidence

Findings should enhance confidence among clinicians and researchers that PHQ-8 is appropriate to screen for depressive symptoms in the clinical context of chronic pain and that the interpretation of screening results is comparable and straightforward. The available evidence does not support the hypothesis that measurement artifacts contribute to elevated rates of positive PHQ-8 screenings in those with chronic pain. On the contrary, the findings underscore the existence of the profound mental health disparities experienced by U.S. adults with chronic pain from end-to-end across the patient journey, including: higher prevalence of clinically significant depressive symptoms, a lower likelihood that such symptoms will be identified, and a lower likelihood of receiving needed mental health support.