Abstract
BACKGROUND: Depression is a leading cause of disability worldwide, requiring reliable and adaptable screening tools. The Patient Health Questionnaire- 9 (PHQ- 9) is widely used, yet its reliability across diverse populations and cultural adaptations remains unclear. OBJECTIVE: This meta-analysis assessed the reliability generalization of the PHQ- 9 across different populations, settings, and cultural contexts to determine its applicability in global mental health assessments. METHODS: A reliability generalization (RG) meta-analysis was conducted on 60 studies with 232,147 participants. A random-effects model was used to estimate pooled internal consistency (Cronbach's α) and test-retest reliability. Subgroup analyses examined the effects of administration modes, cultural adaptations, and study settings. RESULTS: The pooled Cronbach's α was 0.86 (95% CI [0.85, 0.87]), indicating high internal consistency. Test-retest reliability, based on eight studies, was 0.82 (95% CI [0.74, 0.90]). Self-administered formats had the highest reliability (α = 0.87), while face-to-face interviews were lower (α = 0.80). Substantial heterogeneity (I(2) = 99.3%) was observed. CONCLUSIONS: The PHQ- 9 is a reliable depression screening tool globally, but significant heterogeneity highlights the need for continued cultural adaptation and validation to enhance its applicability across diverse contexts.