Development of the New Zealand Adult Reading Test (NZART): Preliminary Findings

The National Adult Reading Test (NART) is used to estimate premorbid intelligence. To establish New Zealand norms for the original NART and develop a New Zealand NART, sixty-three participants were administered Wechsler's Abbreviated Scale of Intelligence (WASI), the NART and the New Zealand Adult Reading Test (NZART). Regression equations were developed to estimate full scale, verbal and performance IQ from the NART and the NZART. Premorbid IQ estimations did not differ between Maori and NZ European participants. The NZART correlated highly with current IQ, was most accurate within the average range and 70% of participants were placed into the correct IQ category. This preliminary study indicates that with further validation the NZART may useful for estimating premorbid IQ in NZ. Accurate diagnosis of cognitive impairment following the onset of illness (e.g., dementia) or injury (e.g., traumatic brain injury) relies upon knowledge of the individual's premorbid level of cognitive functioning (Lezak, Howieson, & Loring, 2004). However, as cognitive testing is uncommon in healthy individuals, this information is rarely available (Hebben & Milberg, 2002). One alternative is to compare an individual's performance to that of a normative sample, but the subtle nature of many cognitive deficits and different patterns of cognitive strengths and weaknesses within each individual mean that such comparisons are not ideal. In particular, comparisons with normative data may under-estimate cognitive decline in previously high functioning individuals and over-estimate deficits in those with lower levels of premorbid intellectual functioning (Green et al., 2008; Lezak et al., 2004). Taking these issues into account, Lezak et al. (2004) suggest that "only an individual comparison provides a meaningful basis for assessing deficit". To overcome this, estimates of premorbid intellectual functioning are frequently employed. To be accurate, these estimates must be reliable, correlate highly with current functioning in healthy individuals and be resistant to cognitive decline (Crawford, 1989; Lezak et al., 2004; Sharpe & O'Carroll, 1991). Such estimates can be obtained by entering historical and observational data (e.g., previous occupation, income, education) into a regression equation (e.g., Barona's formula; Barona, Reynolds, & Chastain, 1984), or on some aspect of their present ability which is resistant to cognitive deterioration (see Reynolds, 1997 for a review of estimation of premorbid IQ). As a New Zealand derived regression equation to predict premorbid IQ is not yet available, local researchers and clinicians use estimates based on current ability (Barker-Collo et al., 2008; Franzen, Burgess, & Smith-Seemillar, 1997). The use of regression equations to estimate current IQ has some problems, namely regression towards the mean and limited range of scores (Strauss, Sherman, & Spreen, 2006). In practical terms this means that the prediction accuracy is poor for IQ scores which deviate significantly from the mean. For those with true IQ scores above the population mean, generally the estimate will be too low, whilst for those with a true IQ below the population mean, the estimate will be too high (Graves, 2000; Veiel & Koopman, 2001). In addition, as these equations are developed based on group data, the derived IQ for any individual only provides an estimate of functioning, rather than an exact IQ (Hawkins, 1995). Given these limitations, it is recommended that estimated IQ data derived from regression equations are supplemented with clinical observations and information about the person's educational and occupational achievements before conclusions are reached regarding impaired functioning as a result of illness or injury (Strauss et al., 2006). Vocabulary based tests are a popular means of estimating premorbid ability, due to their high correlation with education / general ability and evidence suggesting that well learned verbal skills are retained even in those with cognitive deterioration (Crawford, Stuart, Cochrane, Parker, & Besson, 1989; Crawford, Stewart, Garthwaite, Parker, & Besson, 1988; Lezak et al. …