The question of validity of neuropsychological test scores among head-injured litigants: development of a dissimulation index.

Two groups of 20 head-injured subjects were studied. One group was involved in litigation related to the head injury and the other group was not involved in litigation. Every subject had been tested twice, with the intertest mean interval for the two groups ranging from 12.00 to 14.45 months, a statistically insignificant difference. Two indexes of consistency of test-retest performance, which have been reported previously (Reitan Dissimulation Index. Comparison of the distributions for the two groups on the Dissimulation Index revealed no overlap; in fact, a gap of several points separated the groups. Every litigation subject performed with less consistency than any nonlitigation subject. Using an approach based on intra-individual test comparisons shows promise of alleviating the vexing problem of invalidity of neuropsychological test results.