CONTEXT: Previous studies have supported the psychometric properties of the 22-item Zarit Burden Interview (ZBI-22) scale among family caregivers of people with various disorders, including Parkinson´s disease (PD). However, its short-forms have not been psychometrically tested among PD family caregivers, and available psychometric analyses have not accounted for the ordinal nature of item-level data.

OBJECTIVES: To assess the psychometric properties of the ZBI-22 and its short forms among family caregivers of people with PD, while taking account for the ordinal nature of data.

METHODS: Cross-sectional postal survey ZBI-22 data from 66 family caregiver members (59% women; mean age, 69.6 years) of a local Swedish PD society branch were analysed according to classical test theory methods based on polychoric/polyserial correlations.

RESULTS: Missing item responses were ≤5%. Corrected item-total correlations were ≥0.42 and floor-/ceiling effects were <20%, besides for the briefest (4- and 1-item) short-forms (20% and 40% floor effects, respectively). Reliability was good for all scales (ordinal alpha, 0.89-0.95). External construct validity was in general accordance with a priori expectations. Short-forms demonstrated good criterion-related validity (rs 0.87-0.99) and discriminative ability (AUC, 0.91-0.98) relative to the full ZBI-22.

CONCLUSION: This study provides support for the reliability and validity of the ZBI-22 and its various short forms for use among PD family caregivers. In studies where caregiver burden is a central outcome, either ZBI-22 or -12 is suggested for use; other short-forms can be used when caregiver burden is of less central focus or for clinical screening.