Investigating psychometric properties of the Thai version of the Zarit Burden Interview using rasch model and confirmatory factor analysis.

The ZBI-22 fitted the Rasch measurement model regarding unidimensionality but not for ZBI-12. Five items from ZBI-22, and 2 items from ZBI-12 were shown to be misfitting items. Half of ZBI items were shown to be disordered category or threshold, and were locally dependent. CFA revealed three-factor and four-factor fitted the data the best for ZBI-22 and ZBI-12, respectively. Reliability was good for both forms of the ZBI (α = 0.86-0.92). Significant correlations were found with caregiver's perceived stress, anxiety/depression, pain and mobility but not with self-care and usual activity (p > 0.05), indicating convergent and discriminant validity. To conclude, the Thai version ZBI-22, but not ZBI-12, supported the reliability and unidimensional scale among Alzheimer's disease caregivers. Some misfitting items of the ZBI undermined the unidimensionality of the scale, and need revision.