Purpose: To explore the psychometric properties of the full 22-item English (UK and US) version of the Zarit Caregiver Burden Interview administered to caregivers to patients with Duchenne muscular dystrophy.
Materials and methods: Caregivers to patients with Duchenne muscular dystrophy from the United Kingdom and the United States, recruited through the TREAT-NMD network, completed the Zarit Caregiver Burden Interview online. The psychometric properties of the Zarit Caregiver Burden Interview were examined using Rasch analysis.
Results: A total of 475 caregivers completed the Zarit Caregiver Burden Interview. Model misfit was identified for 9 of 22 items (mean item fit residual 0.061, SD: 2.736) and 13 of 22 items displayed disordered thresholds. The overall item-trait interaction chi-square value was 499 (198 degrees of freedom, p < 0.001). The mean person fit residual was estimated at -0.213 (SD: 1.235). The Person Separation Index and Cronbach's α were estimated at 0.902 and 0.914, respectively. Item dependency was low and we found no significant differential item functioning by country or sex.
Conclusion: Our Rasch analysis shows that the Zarit Caregiver Burden Interview fails to fully operationalize a quantitative conceptualization of caregiver burden among caregivers to patients with Duchenne muscular dystrophy from the United Kingdom and the United States. Further research is needed to understand the psychometric properties of the Zarit Caregiver Burden Interview in other populations and settings. Implications for Rehabilitation Duchenne muscular dystrophy is a terminal disease characterized by progressive muscle degeneration resulting in substantial disability and a significant burden on family caregivers. The Zarit Caregiver Burden Interview is one of the most widely applied measures of caregiver burden. Our Rasch analysis suggests that the Zarit Caregiver Burden Interview is not fit for purpose to measure burden in UK and US caregivers to patients with Duchenne muscular dystrophy. Clinicians and decision-makers should interpret Zarit Caregiver Burden Interview data from these populations with caution.
Keywords: DMD; Psychometric analysis; ZBI; disability; patient-reported outcome.