Factor analysis of an outcome interview for use in clinical trials of traumatically brain-injured patients - A preliminary study

Objective: To study the factor structure, internal consistency, concurrent validity, and sensitivity to detect change in patient report of problems of a structured interview in relationship with accepted outcome measures. Design: Outcome status of patients with severe traumatic brain injury parti cipating in a randomized, phase ill, multicenter clinical trial was assesse d at 6 mo postinjury using the Glasgow Outcome Scale, the Disability Rating Scale, and the Severe Traumatic Brain Injury Outcome Interview. Results: Exploratory factor analysis of the Severe Traumatic Brain Injury O utcome Interview produced a meaningful five-factor model: (1) activities of daily living; (2) cognitive; (3) affective; (4) behavioral; and (5) instru mental activities of daily living. The internal consistency of the factors ranged from moderate (0.61 instrumental activities of daily living) to high (0.94 activities of daily living); the interfactor correlations were moder ate. The summed factor scores were significantly correlated with measures o f global outcome: the Glasgow Outcome Scale (r = 0.66; P < 0.0001) and the Disability Rating Scale (r = 0.61; P < 0.0001). Patient report of cognitive problems correlated moderately with the neuropsychological tests. The summ ed factor scores were sensitive to change over time. Conclusions: Overall, the interview assessed the major important features o f outcome pertinent to traumatic brain injury and demonstrated greater sens itivity to subtle changes over time than the unidimensional approaches, suc h as the Glasgow Outcome Scale and Disability Rating Scale.