Credibility of neuropsychological performances of Persian Gulf War veterans and military control subjects participating in clinical epidemiological research.

We investigated whether Persian Gulf War veterans (GWVs) were more likely than Persian Gulf War-era veterans deployed elsewhere (GEVs) to have noncredible neuropsychological examinations. A total of 301 GWVs and 99 GEVs underwent neuropsychological testing. The credibility of 173 examinations showing impairment was evaluated based on test performances, clinical background, psychometric measures, and other self-report data. All 11 examinations judged less than fully credible by one neuropsychologist, plus 19 examinations judged impaired but credible, were then evaluated independently by two more neuropsychologists. Noncredibility was judged with excellent reliability (93% agreement). Seven examinations were judged noncredible. Rates of noncredibility did not differ between GWVs (1%) and GEVs (4%). The pattern of associations of noncredible examinations with cognitive, psychological, and clinical variables generally indicated defective neuropsychological scores, with no coherent pattern, and personality disorder. Findings supported the validity of noncredibility judgments and suggested that noncredible examinations are not a significant problem in neuropsychological investigations of GWVs.