Confirmatory Factor Analysis of the Patient Health Questionnaire-9: A Study of the Participants From the Spinal Cord Injury Model Systems

ObjectiveTo examine the factor structure of the Patient Health Questionnaire-9, a measure of depression, in persons with spinal cord injury (SCI).DesignCross-sectional, confirmatory factor analytic study.SettingCommunity.ParticipantsData for 7296 persons with an SCI who had sustained their injury at least 1 year prior to assessment and who had complete Patient Health Questionnaire-9 data collected at a follow-up interview were drawn from the National Spinal Cord Injury Statistical Center Database.InterventionsNone.Main outcome measuresFactor structure of the Patient Health Questionnaire-9.ResultsConfirmatory factor analysis indicated a marginal fit for the single factor solution (root mean square error of approximation [RMSEA] = 0.086), whereas the solution with 5 somatic items and 4 nonsomatic items had the best fit (RMSEA = 0.054) among 2-factor models that used all 9 items. Of the models that used fewer than 9 items, the best fit was for the 6-item solution with 3 somatic items (sleep, appetite, and fatigue) and 3 nonsomatic items (feeling down, feeling bad about self, and suicidal ideation; RMSEA = 0.043). Similar results were found across the strata except for the Hispanic group (for whom no model fit well).ConclusionsGiven the results of this analysis that support a 2-factor structure of the Patient Health Questionnaire-9 in persons with SCI, the next step in this line of research is to validate each of these dimensions against other ways of measuring depression.