The evaluation of insufficient cognitive effort in schizophrenia in light of low IQ scores

Low IQ has recently been shown to predict neuropsychological effort test failure in healthy and neurological populations. Although low IQ is common in schizophrenia (SZ), its effect on effort test performance remains unclear in this population. The current study examined the role of IQ in effort test performance in a sample of 60 outpatients with SZ and 30 demographically matched healthy controls (CN). Participants were administered a battery of neuropsychological tests, and insufficient effort was calculated using two embedded effort indices: the Reliable Digit Span Effort Index and the Finger Tapping Effort Index. Results indicated that 16.1% of SZ patients and 0% CN failed both effort measures and that 32.1% of SZ and 3.3% of CN failed one measure. In SZ, IQ in the <70 or 70-79 range was associated with the highest rates of falling below the effort cut-off scores; however, patients with IQs in the low-average or higher range (>80) did not fall below effort cut-offs. Findings suggest that low IQ is a significant predictor of insufficient effort during neuropsychological test performance in schizophrenia, calling into question the validity of neuropsychological effort testing in SZ patients with low IQ.