Objectives
The Primary Care Evaluation of Mental Disorders Patient Health Questionnaire (PRIME-MD PHQ-9) is a common screening tool designed to facilitate detection of depression according to DSM-IV criteria. However, the factor structure of the PHQ-9 within the palliative care population has not been evaluated.

Methods
300 participants completed the PHQ-9 within one week of referral to a palliative care service. Participants completed the PHQ-9 again four weeks later (n = 213). Confirmatory factor analysis (CFA) and multiple-group CFA were undertaken to test the factor structure of the PHQ-9 and evaluate model invariance over time.

Results
A two-factor model comprising somatic and cognitive–affective latent factors provided the best fit to the data. Multiple-group CFA suggested model invariance over time. Structural equation modelling revealed that follow-up (time 2) cognitive–affective and somatic symptoms were predicted by their baseline (time 1) factors.

Conclusions
The PHQ-9 measures two stable depression factors (cognitive–affective and somatic) within the palliative care population. Studies are now required to examine the trajectories of these symptoms over time in relation to clinical intervention and events.