Validation of psychometric scales for malingering in a student sample
Objective. To determine South African cut scores for established tests of malingering. Design. A prospective study with an experimental group of subjects that was instructed to feign illness and a control group instructed to perform optimally on a set of psychometric tests. Setting. The study was conducted at the Medical School and main campus of the University of Stellenbosch. Subjects. Seventy-six under- and postgraduate university students. Outcome measures. Each subject completed the Dot-Counting Test (DCT), the Rey 15-item Test (Rey 15-item), the 21-item verbal memory Forced Choice Test (FCT), and the Structured Inventory of Malingered Symptomatology (SIMS). Results. The DCT correctly identified 94% of the feigners by the combined (grouped and ungrouped dots) time score, using a cut-off time of ≤ 63.5 seconds. The Rey 15-item was less specific than the other tests and only the number-of-rows-correct score produced significant results with a correct classification of 88%. A cut score of ≤ 15 for the FCT correctly classified 94% of the malingerers and 100% of the subjects who were asked to perform optimally. The SIMS correctly classified 97% of subjects when a cut score of ≤ 20 was used. Conclusions. The most effective discriminators were the total time to complete the DCT, recognition memory on the 21-item FCT, and the SIMS total score. The results of this study should assist clinicians in South Africa in improving the diagnosis of malingering.