Measuring QoL with SF-36 in Older Americans with TBI

This study demonstrated reliability and factor structure of the Medical Outcomes Study Short-Form Health Survey (SF-36) among
older Americans with Traumatic brain injury (TBI), and evaluated effects of injury severity and race on SF-36’s items and
latent domains. A representative sample of 654 older, racially diverse patients with TBI was selected from the South Carolina
Traumatic Brain Injury Follow-up Registry. Reliability and factor structure of SF-36 were evaluated using Cronbach’s alpha
and confirmatory factor analysis (CFA). Multiple-indicator multiple-causes (MIMIC) models were used to study effects of injury
severity and race on items (differential item functioning, DIF) and latent domains (population heterogeneity) of SF-36. SF-36
was reliable and its current eightfactor structure was confirmed. While TBI severity did not impact latent domain scores of
SF-36, race did. Blacks had higher vitality and lower role-emotional scores than whites. The measurement model was invariant
to injury severity and race (free of DIF), and DIF did not contribute to the differences of vitality and role-emotional between
black and white older TBI patients. SF-36 was valid to measure quality of life (OoL) after TBI in racially diverse elderly
population. Blacks tend to assert to strong coping behaviors in the presence of physical stress while admitting low performance
due to emotional stress. In QoL research where the primary outcomes are usually composite scores from instruments, MIMIC models
have advantages over conventional multivariable regression models in testing the validity of the instruments and assessing
covariate effects on latent traits of instruments while controlling for DIF effects.