Abstract

Objective: Intelligence has recently been shown to predict performance on effort testing in healthy individuals, with lower IQ associated with higher rates of effort test failure. Similar results have been found in patients with epilepsy. However, the relationship between IQ and effort test performance has yet to be examined in psychiatric populations, including schizophrenia (SZ). The current study sought to address this question across two experiments. Method: Participants in Experiment 1 included 97 outpatients with SZ and 63 healthy controls who completed the Victoria Symptom Validity Test (VSVT). Experiment 2 included 46 outpatients with SZ and 33 CN. A very low rate of SZ failed effort testing (VSVT = 1%; WMT = 15%). Patients were separated into WASI full-scale IQ groups (60–79, 80–89, 90–99, 100+) and compared on demographics and effort test performance. Results: Higher current full-scale IQ was associated with higher personal and parental education, higher premorbid IQ, and greater likelihood of being male and Caucasian. IQ in the 60–79 or 80–89 range was associated with greater rates of failure on the WMT and lower scores on the VSVT difficult items. Patients falling above the 90 IQ range did not fail the WMT and had nearly perfect scores on the VSVT. Conclusion(s): Consistent with findings in healthy individuals and individuals with epilepsy, low IQ is a significant predictor of effort test performance in SZ. Our findings indicate that performance on effort tests, which are presumed to be relatively stable even in the face of intellectual deficits, may actually be influenced by intelligence.