Psychometric validation of the patient health questionnaire 4 items for screening anxiety and depression among returned Cambodian migrant workers

Background Ultra-brief mental health screening tools are increasingly needed for large-scale surveys and resource-constrained settings in low- and middle-income countries (LMICs). The Patient Health Questionnaire-4 (PHQ-4) is a widely used instrument for assessing anxiety and depression; however, its psychometric properties have not been validated among returned migrant workers in Cambodia. Methods A cross-sectional study was conducted among 392 returned Cambodian migrant workers recruited across four high-migration provinces in October 2022. Internal consistency was evaluated using Cronbach’s alpha. Confirmatory factor analysis (CFA) compared one-factor and two-factor structural models. Construct validity was evaluated by examining associations between PHQ-4 scores and occupational health risk factors using multivariable logistic regression. Results The sample comprised 392 returned migrant workers (mean age = 34.7 years, SD = 8.9; 52% male, 48% female). The mean overall PHQ-4 score was 2.13 (SD = 2.24) with the majority exhibiting none to mild psychological distress. The PHQ-4 demonstrated acceptable internal consistency ( α = 0.78). CFA supported a two-factor structure representing distinct anxiety and depression dimensions, showing superior model fit compared to the poor fit of the one-factor model (CFI = 0.97, TLI = 0.78, RMSEA = 0.23, SRMR = 0.028). The two-factor model demonstrated excellent fit (CFI = 0.99, TLI = 0.98, RMSEA = 0.035, SRMR = 0.016) and the two latent factors were strongly correlated ( r = 0.79, p < 0.001). Higher PHQ-4 scores were significantly associated with long working hours (AOR = 1.45, 95% CI [1.10, 1.92]), unsafe working conditions (AOR = 1.63, 95% CI [1.21, 2.20]) and hazardous work exposure (AOR = 1.38, 95% CI [1.05, 1.82]) supporting exposure-based construct validity. Conclusions The PHQ-4 is a reliable and valid ultra-brief screening tool for evaluating anxiety and depression among returned Cambodian migrant workers. Evidence supports its application in both occupational settings (workplace surveillance, returnee checks) and non-occupational settings (primary care, NGO community outreach). Its ultra-brief format provides a low-burden, scalable instrument for rapid mental health screening by non-specialized personnel in resource-limited settings across Cambodia.