Detection of sub-optimal performance using a floor effect strategy in patients with traumatic brain injury

This archival study examined the effectiveness of using a normative floor effect method to detect suboptimal performance in a clinical sample of 120 cases consecutively referred for a neuropsychological evaluation. These cases were divided into moderate-severe TBI, mild TBI, and poor effort litigants (demonstrating suboptimal effort). Percentiles, sensitivity, specificity, positive and negative predictive power, and overall correct classification rates were calculated using the moderate-severe TBI sample as the clinical reference group. Several levels of stringency for the floor effect using different base rates were also examined. Setting the floor at the 50th percentile consistently appeared to provide for the best overall hit rate when comparing cases with mild brain injury versus poor effort. At this level, a strong trend (greater than one third of total scores) toward the generation of positive scores offers compelling evidence that, in general, the neuropsychological data have been invalidated by poor motivation. Clinical implications are discussed.