Abstract
BACKGROUND: The study aimed to validate the Zarit Burden Interview (ZBI) in a sample of 942 caregivers of patients with rare diseases (RDs) in Poland. METHODS: The validation process included exploratory and confirmatory factor analyses, as well as an assessment of internal consistency and interpretability. RESULT: Principal Component Analysis was conducted to determine the underlying structure of the scale, identifying a three-factor solution: Personal Sacrifice, Emotional Strain, and Caregiver Guilt and Future Worries. This model was then tested using Confirmatory Factor Analysis, which demonstrated superior model fit compared to a unidimensional approach (CFI = 0.942, TLI = 0.931, SRMR = 0.052, RMSEA = 0.061). Reliability analysis showed strong internal consistency, with Cronbach's alpha values of 0.861 for Personal Sacrifice, 0.848 for Emotional Strain, and 0.722 for Caregiver Guilt and Future Worries. Additionally, weighted scores were introduced for better interpretability, and stratified comparisons by age and sex provided normative references. CONCLUSIONS: Overall, the results confirm that the three-factor model of the ZBI effectively captures caregiver burden and can serve as a reliable tool for assessing the impact of caregiving in diverse populations. The final section provides normative data for the three ZBI subscales among Polish caregivers of individuals with RDs Stratified by sex and age, these norms aid clinicians and researchers in contextualizing individual scores, identifying high-risk groups, and guiding targeted support efforts.