Differential Item Functioning in the WHODAS 2.0 Scale in Schizophrenia: An Application of the Rasch Trees Method Based on Demographic and Clinical Covariates.

Identifying disability score differences in people with schizophrenia according to sociodemographic and clinical variables can help design better rehabilitation or care programs, but in order to compare the scores, it is necessary to confirm the measurement invariance. This study analyses differential item functioning (DIF) in the WHODAS 2.0 (WHO Disability Assessment Schedule) by applying two procedures based on Rasch trees (TREE-PCM and PCM-IFT). A total of 352 patients with schizophrenia spectrum disorder aged between 18 and 55 years took part. Sociodemographic (gender, age, marital status, and education) and clinical (depressive symptomatology, and presence of positive and negative symptoms) covariates were analysed in each of the WHODAS 2.0 domains. The TREE-PCM did not detect DIF, while with PCM-IFT an item with DIF was detected for the age variable. Although the findings suggest that only one item presents DIF, this refers to important issues when assessing functioning in patients with schizophrenia and should be reviewed.