Determining clinically meaningful cognitive impairment following traumatic brain injury

To study the reliability and validity of ratings of: neuropsychological impairment with test data from traumatically brain-injured patients.

Neuropsychological test results from 66 traumatically brain-injured adults and 27 orthopaedic controls were rated for neuropsychological impairment by an experienced neuropsychologist and three undergraduate students provided with brief training in test interpretation. Ratings were based on the discrepancy between a patient's current cognitive level and their estimated premorbid cognitive level. Decision making rules were utilised in making the ratings. The raters, who were blind with respect to the patients diagnostic group membership, independently rated test results. Test results were rerated using the same method approximately two weeks later.

The ratings of novice raters were in good to very good agreement with the ratings of an expert. All raters evidenced very good to excellent test-retest reliability. Higher rates of neuropsychological impairment were found in the traumatically brain-injured group than in the orthopaedic control group. Discriminant function analysis suggested that raters employed information from all neuropsychological measures (with the exception of current intellectual level), in making their overall ratings of neuropsychological impairment.

These findings provide encouraging preliminary evidence in support of the reliability and validity of individual case-based ratings of neuropsychological impairment. The high false positive rate in the control sample may reflect the relatively low specificity of neuropsychological impairment.