Abstract
Ecological momentary assessment is well-suited for capturing rapid symptom dynamics, and it is increasingly used to measure depression symptoms. However, few depression measures are validated for ecological momentary assessment use in the manner expected for traditional questionnaires. Therefore, this study examined the internal consistency, longitudinal stability, and convergent validity of the Mobile Patient Health Questionnaire-9 (MPHQ-9), a version of the Patient Health Questionnaire-9 (PHQ-9) modified for ecological momentary assessment. Depressed participants (N = 280; female = 83.93%; White = 79.29%) completed the MPHQ-9 three times daily for 90 days. Data from the first and last 2 weeks were analyzed to align with a prestudy PHQ-9 and poststudy PHQ-9 and Inventory of Depression and Anxiety Symptoms-II. The MPHQ-9 demonstrated fair to substantial adjusted item-total correlations (r = .42-.83), often exceeding the PHQ-9 (r = .39-.72), with Cronbach's α coefficients of .91 and .81, respectively. Reliability analyses of the MPHQ-9 using generalizability theory and multilevel modeling to account for repeated measures yielded substantial between-person reliability (∼1.0) but mixed within-person reliability estimates of .81 (generalizability theory) and .44 (multilevel modeling). The MPHQ-9 showed moderate stability (r = .69, intraclass correlation coefficient = .58), compared to the slight stability of the PHQ-9 (r = .39, intraclass correlation coefficient = .37). There was moderate agreement between the MPHQ-9 and both the PHQ-9 (r = .71) and the Inventory of Depression and Anxiety Symptoms-II General Depression subscale (r = .65). Supplementary analyses identified short forms with similar convergent validity but reduced symptom-level information. This study provides initial validation of the MPHQ-9 and compares its psychometric properties to the traditional PHQ-9. (PsycInfo Database Record (c) 2026 APA, all rights reserved).