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Abstract
We aimed to develop a word-reading test for Korean-speaking adults using irregularly pronounced words that would be useful for estimation of premorbid intelligence. A linguist who specialized in Korean phonology selected 94 words that have irregular relationship between orthography and phonology. Sixty cognitively normal elderly (CN) and 31 patients with Alzheimer’s disease (AD) were asked to read out loud the words and were administered the Wechsler Adult Intelligence Scale, 4th edition, Korean version (K-WAIS-IV). Among the 94 words, 50 words that did not show a significant difference between the CN and the AD group were selected and constituted the KART. Using the 30 CN calculation group (CNc), a linear regression equation was obtained in which the observed full-scale IQ (FSIQ) was regressed on the reading errors of the KART, where education was included as an additional variable. When the regressed equation computed from the CNc was applied to 30 CN individuals of the validation group (CNv), the predicted FSIQ adequately fit the observed FSIQ (R2 = 0.63). In addition, independent sample t-test showed that the KART-predicted IQs were not significantly different between the CNv and AD groups, whereas the performance of the AD group was significantly worse in the observed IQs. In addition, an extended validation of the KART was performed with a separate sample consisted of 84 CN, 56 elderly with mild cognitive impairment (MCI), and 43 AD patients who were administered comprehensive neuropsychological assessments in addition to the KART. When the equation obtained from the CNc was applied to the extended validation sample, the KART-predicted IQs of the AD, MCI and the CN groups did not significantly differ, whereas their current global cognition scores significantly differed between the groups. In conclusion, the results support the validity of KART-predicted IQ as an index of premorbid IQ in individuals with AD.
Highlights
Obtaining a good estimate for an individual’s premorbid cognitive functioning is critical in research as well as in practice to reliably interpret current cognitive performance or identify cognitive declines
Thirty CN calculation group (CNc), 30 CN individuals of the validation group (CNv), and 31 Alzheimer’s disease (AD) patients were compared on their age, gender distribution, and years of education
The AD group was older than the CNc or CNv groups; mean ages of the CNc and CNv groups did not significantly differ from each other
Summary
Obtaining a good estimate for an individual’s premorbid cognitive functioning is critical in research as well as in practice to reliably interpret current cognitive performance or identify cognitive declines. The NART, developed in England, has been adapted for American English speakers (i.e., AMNART) soon after the development of the NART [5]. Main rationale for such tests is that reading ability is shown to be resistant to mental deterioration due to organic causes [6]. Previous studies have demonstrated that performance on a word reading test is resistant to deterioration in patients with mild to moderate dementia of different etiologies and that its scores are stable after one year of progressive declines in other cognitive functions [7,8,9,10]
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