Construct validity of the Lifespan Sibling Relationship Scale measuring adult sibling relationship quality where one sibling has intellectual or developmental disabilities

The Lifespan Sibling Relationship Scale (LSRS) has been validated in samples where neither sibling has intellectual or developmental disabilities. We sought to examine the construct validity of the LSRS with a sample of adult siblings of people with intellectual or developmental disabilities. Adult siblings of people with intellectual or developmental disabilities (N = 646) completed Adult LSRS items measuring Affect, Behavior, and Cognitions. Confirmatory Factor Analysis (CFA) and Exploratory Factor Analysis (EFA) were employed to examine the construct validity of the LSRS in this sample. The initial CFA fit for a three-factor model was inadequate (CFI = 0.86, TLI = 0.84, RMSEA = 0.10, (Formula presented.) = 1752.97, df = 249). Further analyses using EFA suggested alternative two-factor and three-factor models. CFA models based on these potential factor solutions also had inadequate fit. These findings indicate that the LSRS may not be an appropriate measure of sibling relationships where one sibling has intellectual or developmental disabilities. Future research may need to utilize sibling relationship measures developed specifically for siblings where one has intellectual or developmental disabilities