Estimating pre-morbid ability

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Estimating pre-morbid ability

Neuropsychological assessments are often done to determine if there has been a deterioration in a patient’s functioning due to, for example, dementia or a traumatic brain injury.  The test scores are mostly meaningless, though, if the examiner does not have some indication or an estimate of how the person performed pre-morbidly.  To illustrate, if a patient scores in the average range for most cognitive tests but used to function at a significantly higher level, then the average scores are significantly low.  If you did not know that the patient had such high functioning pre-morbidly, then you might come to the wrong conclusion that his functioning has not deteriorated.

There are several ways to estimate pre-morbid functioning, and research has shown that certain tests are fairly resilient to brain insult (Lezak, 2012).  There does not seem to be any research, though, into the validity of those tests in the South African population.

One of the methods of estimating pre-morbid functioning, is to test a patient’s vocabulary (Lezak, 2012).  Since most of these tests (such as those found in the Wechsler IQ tests) are in English, this approach cannot be used with any confidence with the majority of South Africans whose first language is not English.  Even with English first language speakers, level and quality of education is likely to interfere with the validity of such a method.

Research is needed into suitable measures of pre-morbid functioning for South Africans.

Specific suggestions:

  • Vocabulary tests can be devised for different South African languages and different cultural groups and compared with measures of IQ to determine compatibility.
  • The non-verbal tests that have been found to be resilient to brain injury in westernised groups can be evaluated on South African groups.  Non-verbal tests found to provide good pre-morbid estimations in westernised persons are the Picture Completion (Krull, et al., 1995), Block Design and Object Assembly (Vanderploeg & Schinka, 1995) of the Wechsler tests .  (This research was done using the old WAIS-R and would need to be evaluated using the newest version of the WAIS.).
  • Word-reading tests have been found to be good estimators of pre-morbid ability because they tap into a person’s knowledge of how to pronounce words when they are read.  Examples of these tests are the National Adult Reading Test (NART) and the Wechsler Test of Adult Reading (WTAR).  Research can be done into devising suitable alternatives to these tests in the major South African languages, taking level and quality of education into account.
  • Demographic variables are sometimes used to estimate pre-morbid functioning.  A study can be done on the efficacy of this method in our diverse cultures.
  • Number of years of schooling and quality of schooling (e.g. township schooling vs. private schooling) can be evaluated as a pre-morbid indicator by comparing results of IQ tests done on persons with the different levels and quality of schooling.
  • Occupational history of family members are also often used to help with pre-morbid estimation of patients. The validity of this method can be explored.
  • The Spot the Word test (now in its second edition, Baddeley & Crawford, 2012) is a test to measure pre-morbid functioning and can be used with people who have difficulty with speech.The examinee is required to recognise words and distinguish them from non-words. A study can be done where this test is adapted for various languages spoke in South Africa, where the validity and reliablity is explored (particularly in the light of reading levels of examinees) and normative data collected in the process. Alternately, the test can be kept in its original English form and, the correlation between the test results and English reading level can be explored.

Please leave a reply/comment below, especially if you are thinking of doing this research.


Baddeley A, Emslie H, Nimmo-Smith I. The Spot-the-Word test: a robust estimate of verbal intelligence based on lexical decision. Br J Clin Psychol. 1993;32(1):55-65. doi:10.1111/j.2044-8260.1993.tb01027.x

Krull, K.R., Scott, J.G., & Sherer, M. (1995).  Estimation of premorbid intelligence from combined performance and demographic variables.  The Clinical Neuropsychologist, 9, 83 – 88.

Lezak, M.D., Howieson, D.B., Bigler, E.D., & Tranel, D. (2012).  Neuropsychological Assessment.  Oxford University Press: Oxford.

Vanderploeg, R.D. & Schinka, J.A. (1995).  Predicting WAIS-R IQ premorbid ability: Combining subtest performance and demographic variable predictors.  Archives of Clinical Neuropsychology, 10, 225 – 239.