Note from NeuropsychologySA:
- The reading tests that this article refers to that are excellent at estimating pre-morbid ability, are English tests and will only have validity with English first language examinees. For this reason they are unsuitable for use with most South African examinees.
- The article explains why the “best performance” method of predicting pre-morbid ability tends to over-estimate pre-morbid ability and is therefore not a suitable test of pre-morbid ability.
- The Wechsler sub-tests of Vocabulary, Matrix Reasoning, Information and Picture Completion, regardless of which Wechsler test they are from, are acknowledged in this article as being “hold” tests. That means that these sub-tests are the least likely of the Wechsler sub-tests to be affected by brain damage. However, these sub-tests are not perfect “hold” tests because they can be affected by brain damage. Clinicians using them need be aware of the areas of the brain that are activated when examinees do these sub-tests, because if an examinee has damage in an area of the brain that is needed to do a sub-test, then that sub-test is no longer a good predictor of that examinee’s pre-morbid functioning.
- If the Vocabulary sub-test is only available in English, as is the case with the WAIS-IV, then it can only be validly used as an estimator of pre-morbid functioning with English first language examinees. Informally translating the words into another language while using English normative data for the sub-test, invalidates the test as a measure of pre-morbid functioning.
- Performance on the Information sub-test is strongly affected by level and quality of education. For this reason, if the Information sub-test is used to predict pre-morbid functioning, the normative data used with which the examinee’s test results are compared, need to match the level of and quality of education of the examinee.
- Basing an estimation of pre-morbid ability on demographic factors such as education and occupational status is described as “a course method” in this article and is far from ideal. Considering our limited options for non-English patients, this is still an important method in South Africa but must be used cautiously.
Abstract (taken directly from the article):
To evaluate impact of neurological injury on cognitive performance it is typically necessary to derive a baseline (or “premorbid”) estimate of a patient’s general cognitive ability prior to the onset of impairment. In this paper, we consider a range of common methods for producing this estimate, including those based on current best performance, embedded “hold/no-hold” tests, demographic information, and word reading ability. Ninety-two neurologically healthy adult participants were assessed on the full Wechsler Adult Intelligence Scale – Fourth Edition (WAIS-IV; Wechsler, D. (2008). Wechsler Adult Intelligence Scale (4th ed.). San Antonio, TX: Pearson Assessment.) and on two widely used word reading tests: National Adult Reading Test (NART; Nelson, H. E. (1982). National Adult Reading Test (NART): For the assessment of premorbid intelligence in patients with dementia: Test manual. Windsor: NFER-Nelson.; Nelson, H. E., & Willison, J. (1991). National Adult Reading Test (NART). Windsor: NFER-Nelson.) and Wechsler Test of Adult Reading (WTAR; Wechsler, D. (2001). Wechsler Test of Adult Reading: WTAR. San Antonio, TX: Psychological Corporation.). Our findings indicate that reading tests provide the most reliable and precise estimates of WAIS-IV full-scale IQ, although the addition of demographic data provides modest improvement. Nevertheless, we observed considerable variability in correlations between NART/WTAR scores and individual WAIS-IV indices, which indicated particular usefulness in estimating more crystallised premorbid abilities (as represented by the verbal comprehension and general ability indices) relative to fluid abilities (working memory and perceptual reasoning indices). We discuss and encourage the development of new methods for improving premorbid estimates of cognitive abilities in neurological patients.*In the WAIS-IV, GAI is derived from the core Verbal Comprehension and Perceptual Reasoning subtests.
Bright, P. & van der Linde, I. (2020). Comparison of methods for estimating premorbid intelligence. Neuropsychological Rehabilitation, 30 (1), 1-14.