Accuracy of the Wechsler Test of Adult Reading (WTAR) and National Adult Reading Test (NART) when estimating IQ in a healthy Australian sample

The recently published Wechsler Test of Adult Reading (WTAR) has been co-normed with the third editions of the Wechsler Adult Intelligence and Memory Scales (WAIS-III, WMS-III), and has been shown to reliably estimate intelligence in U.S. and U.K. samples. However, the suitability of the WTAR for use in Australia has not been established, nor is there any clear basis for determining whether to use U.S. or U.K. norms to convert WTAR raw scores to obtain estimates of IQ. This study examined the accuracy with which both the WTAR and the National Adult Reading Test (HART) estimated concurrent WAIS-III IQ performance in a sample of 93 healthy Australian adults who completed all three measures. WTAR reading, demographics, and combined (reading and demographics) estimates of WAIS-III IQ (verbal IQ, full-scale IQ) were calculated using both U.S. and U.K. norms. NART estimates of IQ were also calculated. Although the WTAR and NART IQ estimates all significantly correlated with WAIS-III IQ, there were significant discrepancies between the mean estimated and concurrent IQs. These discrepancies were smallest for the NART. Moreover, the accuracy of all IQ estimates was related to ability level, such that the WTAR and NART overestimated the IQs of persons who were below average in ability and underestimated the IQs of those who were of high average or above average ability. IQs were underestimated or overestimated by as many as 36 or 30 points, respectively. Clinicians are therefore advised to use these measures with caution.