title: Longitudinal measurement invariance of the Dutch Outcome Questionnaire-45 in a clinical sample.
abstract: In the absence of measurement invariance across measurement occasions, change scores based on pretest-posttest measurements may be inaccurate representations of real change on the latent variable. In this study, we examined whether measurement invariance held in the Dutch version of Outcome Questionnaire-45 (OQ-45).
  
  
  
  Using secondary data analysis of a sample of N = 540 Dutch outpatients, we tested the stability of the factorial structure (gamma change) and the metric and scalar invariance (beta change) across pretest and posttest measurements using a combination of factor analysis and item response theory methodology.
  
  
  
  Results revealed a stable factorial structure from pretest to posttest and minor violations of metric invariance for two items in the Dutch OQ-45.
  
  
  
  Even though for two items the assumption of invariance was violated, results suggest that the effects of these violations on practical change assessment using the OQ-45 were negligible.
authors.affiliation: University Medical Center Groningen, University of Groningen, Hanzeplein 1, 9713 GZ, Groningen, The Netherlands.
authors.forename: Ruslan
authors.initials: R
authors.lastname: Jabrayilov
authors.affiliation: Department of Methodology and Statistics, Tilburg School of Social and Behavioral Sciences (TSB), Tilburg University, PO Box 90153, 5000 LE, Tilburg, The Netherlands. w.h.m.emons@tilburguniversity.edu.
authors.forename: Wilco H M
authors.identifier: 0000-0001-7576-0037
authors.initials: WHM
authors.lastname: Emons
authors.affiliation: Institute of Psychology, Clinical Psychology Unit, Universiteit Leiden, PO Box 9555, 2300 RB, Leiden, The Netherlands.
authors.forename: Kim
authors.identifier: 0000-0002-7621-9290
authors.initials: K
authors.lastname: de Jong
authors.affiliation: Department of Methodology and Statistics, Tilburg School of Social and Behavioral Sciences (TSB), Tilburg University, PO Box 90153, 5000 LE, Tilburg, The Netherlands.
authors.forename: Klaas
authors.initials: K
authors.lastname: Sijtsma
mesh_terms: D005006:Ethnicity; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009426:Netherlands; D010045:Outpatients; D063868:Patient Outcome Assessment; D011594:Psychometrics / Q000379:methods; D011788:Quality of Life; D015203:Reproducibility of Results; D057566:Self Report; D011795:Surveys and Questionnaires
keywords: Change assessment; Item response theory; Longitudinal measurement invariance; Outcome Questionnaire 45 (OQ-45); Outcome measurement; Response shift