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On Dimensionality, Measurement Invariance, and Suitability of Sum Scores for the PHQ-9 and the GAD-7.

Accepted version
Peer-reviewed

Type

Article

Change log

Authors

Fried, Eiko I 
Fritz, Jessica 
Russo, Debra A 

Abstract

In psychiatry, severity of mental health conditions and their change over time are usually measured via sum scores of items on psychometric scales. However, inferences from such scores can be biased if psychometric properties such as unidimensionality and temporal measurement invariance for instruments are not met. Here, we aimed to evaluate these properties for common measures of depression (Patient Health Questionnaire-9) and anxiety (Generalized Anxiety Disorder Assessment-7) in a large clinical sample (N = 22,362) undergoing psychotherapy. In addition, we tested consistency in dimensionality results across different methods (parallel analysis, factor analysis, explained common variance, the partial credit model, and the Mokken model). Results showed that while both Patient Health Questionnaire-9 and Generalized Anxiety Disorder Assessment-7 are multidimensional instruments with highly correlated factors, there is justification for sum scores as measures of severity. Temporal measurement invariance across 10 therapy sessions was evaluated. Strict temporal measurement invariance was established in both scales, allowing researchers to compare sum scores as severity measures across time.

Description

Keywords

GAD-7, PHQ-9, dimensionality, measurement invariance, sum scores, Anxiety, Anxiety Disorders, Depression, Humans, Patient Health Questionnaire, Psychometrics, Reproducibility of Results

Journal Title

Assessment

Conference Name

Journal ISSN

1073-1911
1552-3489

Volume Title

Publisher

SAGE Publications

Rights

All rights reserved
Sponsorship
National Institute for Health Research (NIHR) (via Cambridgeshire and Peterborough NHS Foundation Trust (CPFT) (RP PG-0616-20003)
Medical Research Council (1800905)
National Institute for Health and Care Research (NIHR200177)
NIHR