Further validation of the New Zealand test of adult reading (NZART) as a measure of premorbid IQ in a New Zealand sample

Neuropsychological assessments are frequently conducted to evaluate changes in cognitive functioning resulting from brain injury or degenerative decline (Lezak, 2004). To evaluate cognitive decline, comparisons between current and premorbid functioning need to be made, however as baseline assessment results are rarely available estimates of premorbid functioning are often used. The suitability of these measures depends on the resilience of the underlying cognitive domains to neurological disorders and their strong correlation with current Intelligence Quotient (IQ) in the absence of neurological disorder (Lezak, 2004). As such, one of the most commonly used methods for estimating premorbid IQ focuses on current skills which are relatively resistant to brain injury, such as word reading. Reading skills, and in particular single word reading skills, have been shown to be relatively free from the influence of age and gender (Crawford, Parker, & Besson, 1988), psychiatric diseases such as depression and schizophrenia (Crawford, 1992), and are resilient to mild to moderate dementia (McGurn et al., 2004), and mild to moderate traumatic brain injury (TBI) (Watt & O'Carroll, 1999). Reading skills are also highly correlated with IQ, a measure of the individuals' overall level of cognitive functioning (Crawford, Stewart, Cochrane, Parker, & Besson, 1989). One of the most widely used premorbid assessment tools based on current single word reading skills is the National Adult Reading Test (NART) (Nelson & Willison, 1991), which has been standardised against the Wechsler Adult intelligence Scale-Revised Edition (WAIS-R). The WAIS scales are viewed as the 'gold standard' of IQ tests to which assessments of premorbid function are compared (Lezak, 2004; Silverman, 2010). The NART was developed in Great Britain to assess the severity of dementia. It consists of 50 single words which are irregular in their grapheme-to-phoneme translation. Thus, if the reader is unfamiliar with a word they are likely to pronounce it incorrectly (Nelson & Willison, 1991). The NART error score is inserted into a regression formula provided in the test manual to obtain an estimated premorbid IQ score. The NART has a high split half reliability (r = .93), high inter-rater reliability (r = .96 to r = .98) and high test-retest reliability (r = .98) (Nelson & Willison, 1991). Criterion validity of the NART is reported to be good, explaining between 61% and 72% of the variance in Verbal IQ (VIQ), 55% to 66% of the variance of Full Scale IQ (FSIQ) scores, and 32-33% of the variance of Performance IQ (PIQ) (Crawford, Deary, Starr, & Whalley, 2001; Crawford, Stewart, Cochrane, Parker, et al., 1989; Sharpe & O'Carroll, 1991). The NART has been used extensively in Great Britain and other countries, either in its original form (Barker-Collo et al., 2008; McGurn et al., 2004; Watt & O'Carroll, 1999) or modified to better suit linguistic differences. The North American Adult Reading Test (NAART) (Blair & Spreen, 1989), the American National Reading Test (AMNART) (Gladsjo, Heaton, Palmer, Taylor, & Jeset, 1999) and the AUSNART (Hennessy & Mackenzie, 1995) in Australia are examples of modified versions of the NART. The addition of demographic variables (e.g., age, gender, years of education and occupation (Barona, Reynolds, & Chastain, 1984) to the NART-based regression formulae has been found to increase the formulae's accuracy of premorbid IQ prediction (Bright, Jaldow, & Kopelman, 2002; Crawford et al., 1988; Crawford, Stewart, Cochrane, Foulds, et al., 1989; Watt & O'Carroll, 1999). Other reading-based tests of premorbid functioning are also available, for example the Test of Premorbid Functioning (TOPF) (The Psychological Corporation, 2009) and its predecessor the Wechsler Test of Adult Reading (WTAR) (Wechsler, 2001). The WTAR, co-normed with the WAIS-III has been used widely due to its' large U. …