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Measurement stability and differential domain-specific trajectories of the PHQ-9 in late-life depression: Evidence from a collaborative care trial
Date
2026-11-01
Abstract
Background: The Patient Health Questionnaire-9 (PHQ-9) is routinely used to monitor depressive symptoms. However, whether its empirically derived two-factor structure remains stable across repeated assessments in clinically depressed populations is not well established. Methods: Using item-level data from a secondary analysis of the PROACTIVE cluster-randomised controlled trial (𝑁 = 558; PHQ-9 ≥ 10 at baseline; aged ≥ 60 years), we evaluated longitudinal measurement invariance of an empirically derived two-factor PHQ-9 structure across three assessment points using WLSMV structural equation modelling with multiple imputation. We then modelled domain-specific latent growth trajectories by trial arm and examined within-person temporal dynamics using a random intercept cross-lagged panel model (RI-CLPM). Results: Metric invariance was supported and partial scalar invariance achieved across all three time points, after freeing thresholds for three interpretable items (sleep disturbance, fatigue, and suicidal ideation). The intervention was associated with a steeper improvement in cognitive-affective symptoms but showed no significant effect on somatic symptom trajectories. Within-person somatic deviations at baseline were temporally associated with subsequent cognitive-affective deviations, whereas the reverse was not. Conclusions: The two-factor structure of the PHQ-9 is metrically stable through clinical recovery in older adults with moderate-to-severe depression. Domain-specific subscores capture differential treatment response and temporal symptom dynamics that total scores conceal, and can be calculated from existing PHQ-9 items at no additional burden. These findings support the routine use of domain-level monitoring in collaborative care programmes serving older adults in low- and middle-income country (LMIC) settings
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Publisher
Elsevier
Citation
Journal of Affective Disorders 413, 122171
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Funding Information
Sustainable Development Goals
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License
Attribution-NonCommercial-ShareAlike 4.0 International