Patient Health Questionnaire-9 scores do not accurately estimate depression prevalence: individual participant data meta-analysis

Depression symptom questionnaires are not for diagnostic classification. Patient Health Questionnaire-9 (PHQ-9) scores ≥10 are nonetheless often used to estimate depression prevalence. We compared PHQ-9 ≥10 prevalence to Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders (SCID) major depression prevalence and assessed whether an alternative PHQ-9 cutoff could more accurately estimate prevalence. Individual participant data meta-analysis of datasets comparing PHQ-9 scores to SCID major depression status. A total of 9,242 participants (1,389 SCID major depression cases) from 44 primary studies were included. Pooled PHQ-9 ≥10 prevalence was 24.6% (95% confidence interval [CI]: 20.8%, 28.9%); pooled SCID major depression prevalence was 12.1% (95% CI: 9.6%, 15.2%); and pooled difference was 11.9% (95% CI: 9.3%, 14.6%). The mean study-level PHQ-9 ≥10 to SCID-based prevalence ratio was 2.5 times. PHQ-9 ≥14 and the PHQ-9 diagnostic algorithm provided prevalence closest to SCID major depression prevalence, but study-level prevalence differed from SCID-based prevalence by an average absolute difference of 4.8% for PHQ-9 ≥14 (95% prediction interval: −13.6%, 14.5%) and 5.6% for the PHQ-9 diagnostic algorithm (95% prediction interval: −16.4%, 15.0%). PHQ-9 ≥10 substantially overestimates depression prevalence. There is too much heterogeneity to correct statistically in individual studies. •We compared Patient Health Questionnaire-9 (PHQ-9) ≥ 10 prevalence with Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders (SCID) major depression prevalence in 44 primary studies (9,242 participants and 1,389 SCID major depression cases) that administered the PHQ-9 and SCID.•We also examined whether an alternative PHQ-9 cutoff could more accurately estimate prevalence.•Pooled PHQ-9 ≥10 prevalence (25%) was double-pooled SCID major depression prevalence (12%); pooled difference from each study was 12%.•PHQ-9 ≥14 and PHQ-9 diagnostic algorithm prevalence most closely matched SCID major depression prevalence, but study-level PHQ-9 ≥14 and PHQ-9 diagnostic algorithm prevalence differed from SCID major depression prevalence with 95% prediction intervals of −14% to 15% and −16% to 15%, respectively.•Estimates of depression prevalence should be based on validated diagnostic interviews designed for determining case status; users should evaluate published reports of depression prevalence to ensure that they are based