Longitudinal measurement invariance of the patient health questionnaire in a German sample

Abstract

Background The Patient Health Questionnaire-8 (PHQ-8) is a screening questionnaire of depressive symptoms. However, it is unknown whether it is equivalent across time and between groups of individuals. The aim of our paper was to test whether the PHQ-8 has the same meaning in two groups of individuals over time. Methods Primary care patients were proactively recruited from three German cities. PHQ-8 data from a baseline assessment (n = 588), two assessments during the intervention (n = 246/225), and a six (n = 437) and 12 months (n = 447) follow-up assessment were first used to examine the factor structure of the PHQ-8 by confirmatory factor analysis (CFA). The best fitting factor solution was then used to test longitudinal invariance across time and between intervention and control group by Multiple Group CFA. Results A two-factor structure consistently showed the best model fit. Only configural longitudinal invariance was evidenced when the baseline assessment was included in the analysis. Without the baseline assessment, strict longitudinal invariance was shown across the intervention and the follow-up assessments. Scalar invariance was established between the intervention and control group for the baseline assessment and strict invariance between groups and across the 6- and 12-month follow-up assessments. Conclusions The lack of longitudinal invariance might be attributed to various differences between the baseline assessments and all following assessments, e.g., assessment mode (iPad vs telephone), potential changes in symptom perception, and setting. Trial registration DRKS00011635, date of trial registration: 20.01.2017; DRKS00011637, date of trial registration: 25.01.2017.

Longitudinal invariance of the Patient Health Questionnaire–9 among patients receiving pharmacotherapy for major depressive disorder: A secondary analysis of clinical trial data.

“…One potential explanation for this could be that, unlike the other PHQ-9 items, Item 9 was heavily skewed toward the least severe response. Because our study goal was to examine the LMI of the PHQ-9 and not the reduced PHQ-8 scale that omits Item 9 (which has also seen similar mixed findings in previous studies, e.g., Dong et al, 2022; Downey et al, 2016; Moehring et al, 2021), we only explored PHQ-8 LMI in a full-sample one-factor sensitivity analysis and not across veteran subgroups. Future research could help determine if Item 9 provides additional clinical utility over the remaining eight items with regards to the longitudinal monitoring of depressive symptoms.…”