Do somatic symptoms bias depression screening? Reliability and equivalence of PHQ-8 in those with and without chronic pain: A nationally representative study of U.S. adults.

The 8-item Patient Health Questionnaire (PHQ-8) is implemented into clinical practice and scientific research worldwide. However, in the context of chronic pain (CP), depression screening could be confounded by overlapping somatic symptoms. Inaccurate attribution of CP symptoms to depression could lead to overestimation of depressive symptom severity or even artifactual inflation of depression prevalence estimates. We aimed to determine the reliability and equivalence of PHQ-8 in adults with and without CP. This nationally representative survey study examined data from the 2019 National Health Interview Survey. The final analytic sample contained (n = 30,983) U.S. adults who completed survey items on CP and the PHQ-8. Descriptives and visualizations were generated; reliability, cross-group equivalence, and measurement invariance were assessed. The PHQ-8 was reliable; measurement invariance and cross-group equivalence were observed at the configural, metric, and scalar levels; differential item functioning was not observed. No evidence consistent with overestimation of depression prevalence or severity in the contexts of CP or HICP was observed. The PHQ-8 is reliable and measures depressive symptoms equivalently in the context of CP, supporting the use of PHQ-8 to screen for depression in clinical practice, scientific research, and population health surveillance of adults with and without CP. CP is regularly observed to be associated with five to ten times greater prevalence of positive screens for clinically significant depressive symptoms. This study offers compelling evidence that this disparity reflects true differences in the prevalence of depression in those with chronic pain and is not attributable to measurement artifacts.