Word Memory Test failure 23 times higher in mild brain injury than in parents seeking custody: the power of external incentives.

PRIMARY OBJECTIVE Motivation has an important influence on neuropsychological test performances. This study examined effort on the Word Memory Test (WMT) in groups with differing external incentives. RESEARCH DESIGN 774 adults with Traumatic Brain Injury (TBI), tested as part of a Workers' Compensation, disability or personal injury claim stood to gain financially by appearing impaired on testing. In contrast, parents ordered by the Court to undergo a parenting assessment were highly motivated to do their best on cognitive tests because their goal was to regain custody of their children. OUTCOMES AND RESULTS Consistent with these assumptions, 98.3% of 118 parents seeking child custody passed the WMT effort subtests but in cases of mild TBI the pass rate on the WMT was only 60%. The WMT failure rate in the mild TBI sample was 23 times higher than in the group of parents seeking custody. WMT failure was twice as frequent in the mild TBI group than in those with more severe TBI. WMT failure was also much higher in adults with mild TBI than in children with significant impairment from various clinical conditions. CONCLUSIONS Such differences in failure rates on the WMT effort subtests cannot be explained by differences in cognitive skills but they are explainable by differences in external incentives. The findings support the recommendation that objective tests of effort should be used when evaluating cognitive impairment.