Validation of two short versions of the Zarit Burden Interview in the palliative care setting: a questionnaire to assess the burden of informal caregivers

Purpose: Several validated outcome measures, among them the Zarit Burden Interview (ZBI), are valid for measuring caregiver burden in advanced cancer and dementia. However, they have not been validated for a wider palliative care (PC) setting with non-cancer disease. The purpose was to validate ZBI-1 (ultra-short version and proxy rating) and ZBI-7 short versions for PC. Methods: In a prospective, cross-sectional study with informal caregivers of patients in inpatient (PC unit, hospital palliative support team) and outpatient (home care team) PC settings of a large university hospital, content validity and acceptability of the ZBI and its structural validity (via confirmatory factor analysis (CFA) and Rasch analysis) were tested. Reliability assessment used internal consistency and inter-rater reliability and construct validity used known-group comparisons and a priori hypotheses on correlations with Brief Symptom Inventory, Short Form-12, and Distress Thermometer. Results: Eighty-four participants (63.1% women; mean age 59.8, SD 14.4) were included. Structural validity assessment confirmed the unidimensional structure of ZBI-7 both in CFA and Rasch analysis. The item on overall burden was the best item for the ultra-short version ZBI-1. Higher burden was recorded for women and those with poorer physical health. Internal consistency was good (Cronbach's α = 0.83). Inter-rater reliability was moderate as proxy ratings estimated caregivers' burden higher than self-ratings (average measures ICC = 0.51; CI = 0.23-.69; p = 0.001). Conclusion: The ZBI-7 is a valid instrument for measuring caregiver burden in PC. The ultra-short ZBI-1 can be used as a quick and proxy assessment, with the caveat of overestimating burden.