PHQ-8 scores and estimation of depression prevalence


In the Article by Jorge Arias-de la Torre and colleagues the authors used data for 258,888 individuals obtained from the second wave of the European Health Interview Survey to estimate depression prevalence in 27 European countries based on scores of 10 or higher on the eight-item Patient Health Questionnaire (PHQ-8). The authors reported an overall prevalence of current depressive disorder of 6·38% (95% CI 6·24–6·52) with substantial heterogeneity across countries. Depression symptom questionnaires and standard cutoffs, such as PHQ-8 scores of 10 and higher, are not intended to estimate disorder prevalence, but are designed for screening purposes; they are intended to identify a higher number of individuals than would be diagnosed with depression if assessed using validated diagnostic criteria. An individual participant data meta-analysis of 44 studies,3 which included 9242 participants (of whom 1389 had Structured Clinical Interview for DSM [SCID] major depression) found that, on average, prevalence based on nine-item Patient Health Questionnaire (PHQ-9) scores of 10 or higher (which perform similarly to scores of 10 or higher on the PHQ-84) overestimated SCID-based prevalence by 11·9%. In the 44 studies, the mean ratio of PHQ-9 scores of 10 or higher to SCID-based prevalence was 2·5. Consistent with evidence that PHQ-9 scores of 10 or higher exaggerate prevalence, although the PHQ-8 assesses symptoms in the previous 2 weeks, in the European Health Interview Survey, the prevalence of current depressive disorder was higher than 12-month European prevalence based on a validated diagnostic interview. Depression is an important concern. However, using the proportion of individuals with scores above screening cutoffs on self-report questionnaires does not generate valid prevalence estimates, and the estimates reported by Arias-de la Torre and colleagues are not likely to represent the actual prevalence of depression in Europe. There are ways to incorporate self-report questionnaires into methods for estimating prevalence, but simply reporting the proportion of participants with positive screens is not recommended. We declare no competing interests.

THE LANCET: Public Health
Felix Fischer
Felix Fischer
Group Leader Psychometrics and Health Outcomes

Psychologist with a weakness for quantitative data analysis