Traumatic brain injury (TBI) may lead to enduring cognitive end emotional deficits. Assessment of such deficits by psychological testing requires testing for effort and cooperativeness, especially when litigation is involved. How strong is the effect of effort and does lesion site, especially frontal lobe damage, influence effort?

N= 208 subjects with TBI were assessed between 2004 and 2006 by a neurological, a psychiatric and a psychological examination. The referral sources were the German workers compensation board and private insurance companies. The psychological battery comprised measures of memory, attention, cognitive speed and intelligence as well as self report instruments for assessment of psychiatric symptoms. Effort was assessed with the WMT (Green 2003). Lesion site and type was available through reports on brain CAT scans and MRIs. Assessment was done a median 25 months after the injury.

The results indicate that effort explained the largest share (50%) of the variance in psychological tests scores. There was no effect for lesion site on effort. A factor analysis on test scores produced a two factor solution, with the largest loadings on effort.

It is evident that in cases involved in litigation the performance in neuropsychological assessment is mainly explained by effort. However, there was no evidence, that injury to some brain areas would specifically impair effort. The study adds support to the construct validity of effort testing and its robustness in frontal lobe damage.