Estimating Premorbid IQ in New Zealand

The experience of brain injury changes the world for the person experiencing it and their family. It is important for health providers to know as accurately as possible how severe the brain damage is to be able to deliver the appropriate level of treatment and rehabilitation. Tests are available to measure current cognitive functioning which can be expressed as an intelligence quotient (IQ). One such test is the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV). Other tests are able to estimate premorbid IQ, for example the National Adult Reading Test (NART), the Test of Premorbid Functioning (TOPF) and the New Zealand Adult Reading Test (NZART). The discrepancy between the current IQ and the estimated premorbid IQ scores provides an estimate of the decrease in cognitive function as a result of brain injury. Most of these IQ tests have not been developed or normed for the New Zealand population and their suitability for this population is therefore not known. This study aimed to evaluate the ability of the tests of premorbid IQ to estimate the current WAIS-IV IQ in a New Zealand sample. This sample consisted of 86 New Zealand born, neurologically healthy, men and women (mean age of 46 years), who were administered the WAIS-IV, NART, TOPF and NZART. The results showed that the tests of premorbid IQ significantly over estimated lower IQ scores and significantly under estimated higher IQ scores. New regression formulae for the NART, TOPF and NZART were developed based on the WAIS-IV FSIQ and were found to be only marginally better at predicting current IQ. These new regression formulae also over-and under-estimated current IQ in the lower and upper ranges. The NZART, a New Zealand developed test, showed slightly better performance than the overseas tests. It was concluded that the tests of premorbid functioning are not very accurate in in their prediction of WAIS-IV current IQ for people in New Zealand and alternative methods of estimating premorbid IQ are suggested

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

Premorbid IQ estimates are used to determine decline in cognitive functioning following trauma or illness. This study aimed to: 1) further validate the New Zealand Adult Reading Test (NZART) in a New Zealand population and compare its performance to the UK developed National Adult Reading Test, and 2) develop regression formulae for the NZART to estimate Wechsler Adult Intelligence Scale-IV (WAIS–IV) IQ scores. The 67 participants (53 females; 16 Māori), aged 16 to 90 years old (mean age = 46.07, SD 23.21) completed the WASI-IV, the NART and the NZART. The NZART predicted Verbal Comprehension Index (VCI) scores slightly better than the NART (r =.63 vs. r = .62) and explained 33% of the variance in FSIQ scores. Reasons for developing regression formulae for the NZART are discussed, regression formulas for the NZART based on the WAIS–IV are included and suggestions of alternate ways of determining premorbid IQ are made

The Detection of subtle cognitive differences

Abstract Background: Physical health and age both influence cognitive functioning. The detection of subtle cognitive differences is particularly important, as these differences might be early indicators of pathological processes. Early detection is central to earlier commencement of treatment. However, few existing measures are available to detect subtle cognitive change within people or difference between people. Aim: This thesis examines the detection of subtle cognitive change in people with Coeliac Disease (CD) and subtle cognitive difference between healthy, elderly people to determine if subtle cognitive difference and change can be detected in the domains of episodic memory, processing speed and response accuracy. These three domains were chosen because previous research has shown that these domains are vulnerable to pathological processes. Methods: In Study 1, 11 participants with CD were administered seven cognitive tests at four time points over the 12 months study period. Blood and duodenal biopsy samples were also obtained at three time points during the first 12 months following the participants’ commencement of a gluten free diet. In the systematic literature review for Study 2, cognitive tests used in 59 publications were reviewed for their ability to detect subtle cognitive difference between healthy people and those with mild cognitive impairment (MCI) in the domains of episodic memory, processing speed and response accuracy. In Study 3, the choice reaction time (CRT) and accuracy (A) scores of the Subtle Cognitive Impairment Test (SCIT), administered to 182 community dwelling, neurologically healthy elderly people (age range from 60 to 89 years), were used to create a performance measure able to detect subtle cognitive differences between the participants. Scores were standardised, and cluster analysis performed to create three performance groups based on subtle cognitive differences in CRT and A. In Study 4, the scores of eight further cognitive tests were examined with non-parametric tests for differences between the three performance groups. Results: For the first time, subtle cognitive improvement in people with CD on a gluten free diet was proven to exist and was measured. The systematic literature review showed that the Hopkins Verbal Learning Test (HVLT) was able to detect subtle cognitive differences, but that too few measures of processing speed and response accuracy were used by the included publications to allow comparison. A performance measure was created that was able to discriminate between good, cautious and impulsive performer profiles based on differences in CRT and A. Significant differences in performance between the three profiles were found in the domains of memory (verbal episodic, semantic memory and nonverbal visuospatial memory), executive functioning (attention and accuracy) and processing speed (decision speed and perceptual speed). Good performers performed better than cautious performers, and these differences were significant in four out of 12 tests and subtests. Cautious performers performed better than impulsive performers in 10 of 12 tests. Relative to good performers, impulsive performers performed significantly worse in nine tests and subtests (p < 0.017). Conclusion: Subtle cognitive change and difference is detectable in people with CD and in the healthy elderly. This ability to detect subtle change and difference can be used to screen and monitor people at risk of health or age related cognitive changes

The Detection of subtle cognitive differences

Abstract Background: Physical health and age both influence cognitive functioning. The detection of subtle cognitive differences is particularly important, as these differences might be early indicators of pathological processes. Early detection is central to earlier commencement of treatment. However, few existing measures are available to detect subtle cognitive change within people or difference between people. Aim: This thesis examines the detection of subtle cognitive change in people with Coeliac Disease (CD) and subtle cognitive difference between healthy, elderly people to determine if subtle cognitive difference and change can be detected in the domains of episodic memory, processing speed and response accuracy. These three domains were chosen because previous research has shown that these domains are vulnerable to pathological processes. Methods: In Study 1, 11 participants with CD were administered seven cognitive tests at four time points over the 12 months study period. Blood and duodenal biopsy samples were also obtained at three time points during the first 12 months following the participants’ commencement of a gluten free diet. In the systematic literature review for Study 2, cognitive tests used in 59 publications were reviewed for their ability to detect subtle cognitive difference between healthy people and those with mild cognitive impairment (MCI) in the domains of episodic memory, processing speed and response accuracy. In Study 3, the choice reaction time (CRT) and accuracy (A) scores of the Subtle Cognitive Impairment Test (SCIT), administered to 182 community dwelling, neurologically healthy elderly people (age range from 60 to 89 years), were used to create a performance measure able to detect subtle cognitive differences between the participants. Scores were standardised, and cluster analysis performed to create three performance groups based on subtle cognitive differences in CRT and A. In Study 4, the scores of eight further cognitive tests were examined with non-parametric tests for differences between the three performance groups. Results: For the first time, subtle cognitive improvement in people with CD on a gluten free diet was proven to exist and was measured. The systematic literature review showed that the Hopkins Verbal Learning Test (HVLT) was able to detect subtle cognitive differences, but that too few measures of processing speed and response accuracy were used by the included publications to allow comparison. A performance measure was created that was able to discriminate between good, cautious and impulsive performer profiles based on differences in CRT and A. Significant differences in performance between the three profiles were found in the domains of memory (verbal episodic, semantic memory and nonverbal visuospatial memory), executive functioning (attention and accuracy) and processing speed (decision speed and perceptual speed). Good performers performed better than cautious performers, and these differences were significant in four out of 12 tests and subtests. Cautious performers performed better than impulsive performers in 10 of 12 tests. Relative to good performers, impulsive performers performed significantly worse in nine tests and subtests (p < 0.017). Conclusion: Subtle cognitive change and difference is detectable in people with CD and in the healthy elderly. This ability to detect subtle change and difference can be used to screen and monitor people at risk of health or age related cognitive changes