Factor analysis and Rasch analysis of the Zarit Burden Interview for acquired brain injury carer research.

OBJECTIVE: To examine the dimensionality of the Zarit Burden Interview in a sample of carers of adults with acquired brain injury.

DESIGN: A cross-sectional UK survey using postal questionnaires.

PARTICIPANTS: A sample of 222 carers; 43 men (19.4%) and 179 women (80.6%); mean age 54 years. Types of brain injury included traumatic brain injury (49.5%), stroke (25.9%), brain infection (17.3%), hypoxia (4.1%), and "other" (3.2%).

METHODS: Exploratory and confirmatory factor analysis and Rasch analysis.

RESULTS: Unidimensionality was tested using confirmatory factor analysis, which showed a poor fit. The underlying structure of the Zarit Burden Interview was explored using principal components analysis and varimax rotation. This revealed 3 factors, although 1 comprised only 2 items. The 2 major factors identified were personal strain and role strain. They were then examined using Rasch analysis, which identified 2 brief and reliable unidimensional scales. There was no evidence of differential item functioning for different types of carer/brain injury.

CONCLUSION: The Zarit Burden Interview is a promising mea-sure for the assessment of burden in carers of people with an acquired brain injury. It offers 2 reliable, brief subscales of personal strain and role strain for this purpose. However, it remains for these 2 brief subscales to be validated clinically in future research.