Special Guest Blogger! Dr Sylvia Moody writes on IQ testing in dyslexia assessment

IQ?  Leave it out!    Cognitive profile?  Leave it in…

Sylvia Moody

I’m writing this article to try to correct some misconceptions about the use of an IQ battery in dyslexia assessments.


  1. My comments are relevant to assessors of dyslexic adults; assessors of dyslexic children may have a different perspective on the matter in question.
  2. I have been working as an assessor of adults in both HE and the workplace for twenty years. During this period I have viewed or re-viewed hundreds of dyslexia assessment reports, written by both psychologists and – in more recent years – specialist teachers.
  3. Though I am myself a psychologist, I am not writing this article solely from a psychologist’s perspective; for nearly ten years I have been co-ordinating a CPD group which consists almost wholly of experienced PATOSS assessors – and so I have had ample opportunity to discuss with specialist teachers their opinions and/or concerns about dyslexia assessment.

Uses of an IQ test battery

One may sometimes hear the following statement made:

‘It is not useful to use an IQ battery in a dyslexia assessment.’

 But this statement is meaningless. Whether an IQ battery is useful or not in a dyslexia assessment depends on how and for what purpose the battery is being used. The Wechsler test, for example can be used for two purposes:

(a)   to obtain a set of IQ scores;

(b)   to obtain a cognitive profile, ie, scores on tests of verbal ability,

perception (non-verbal ability), working memory and processing speed.

In a dyslexia assessment (a) is unlikely to be useful, but (b) is essential.

An example of a situation in which IQ scores would be useful is as follows:

A client comes to me and says ‘I want to join MENSA. Please will you test me?’ I would then administer the WAIS and calculate the IQ scores, as I assume that these are what MENSA requires.

An example of a situation in which IQ scores would not be useful is as follows:

A client comes to me and says: ‘I think I’m dyslexic. Will you test me?’ In this case I  would administer the WAIS but not calculate the IQ scores; I would simply obtain a cognitive profile, ie. the scores on the sub-tests and (if appropriate) the index scores.

Of course, if a particular examination board required IQ scores, then I would calculate them so as to smooth the way for my client, even though I myself regarded them as otiose.

Reasons not to calculate IQ scores

It seems to be the case that the majority of assessors – whether they be psychologists or specialist teachers – do quote IQ scores in a dyslexia assessment. But it is hard to understand why. There are at least three reasons for not doing so:

  1. Statistical

It is stated in IQ manuals that, if the differences between sub-test scores are significant at the clinical level, then it is inappropriate (because misleading) to give IQ scores. In other words if there is a pronounced spiky profile, IQ scores become meaningless – they are uninformative ‘average’ scores which mask the strengths and weaknesses usually found in a dyslexia profile.

  1. Technical

If an assessor calculates IQ scores, presumably he/she feels that they are of some use. But it is difficult to see what use they could be in the context of adult dyslexia assessment, given that the scores are not going to be compared with anything, and that we are not testing for IQ.

On this point I will quote informal guidance recently received from Dr David McLoughlin, Chairman of the SpLD Test Evaluation Committee:

“I do not use the WAIS as an IQ test, but as a measure of four competencies [verbal/non-verbal abilities, memory, processing speed]. On the Wechsler scale,

the verbal comprehension index score provides a better predictor than

an overall IQ of attainment in reading, spelling and writing.”

  1. Pragmatic

Dyslexia reports on adults are read by many people outside the educational world, e.g., employers, lawyers, HR and occupational health professionals. Such readers rarely take the time to read our reports in detail; they tend to look at the Summary, Conclusions and Recommendations. So quoting a composite IQ score can give a misleading impression.

An example:

Maria, twenty-six years of age, had just completed a Law degree and gained a 2,1. She had begun work, as a probationer, in the legal department of a multinational company. She had difficulty finishing work on time, and was becoming increasingly prone to careless errors. She referred herself for a dyslexia assessment, which was carried out by a psychologist.

The WAIS results showed that Maria had verbal and perceptual (non-verbal) abilities in the high range, while her memory and processing speed scores were just below average. Although the differences between several sub-test scores were clinically significant, the psychologist had nonetheless calculated the IQ scores – and these were all in the average range.

In her report the psychologist began the first-page Summary of her findings with the phrase: “Maria is a woman of average abilities…”. Although the scores had been analysed in more detail in the body of the report, this section of the report was written in too technical a way for the relevant managers to understand it. They focussed on the ‘average abilities’ phrase and argued that Maria did not have the intellectual ability to do her job.

Fortunately in this case Maria sought a second opinion from a different psychologist, and the latter was able to explain the assessment results to the managers in a more informative way. After this Maria was able to continue in her job with the help of relevant support.

WRIT-based cognitive profile

Obtaining a WRIT-based cognitive profile is a slightly more tricky process than obtaining a cognitive profile on the WAIS. The WAIS includes all the tests one needs to measure the

level of a client’s verbal and non-verbal abilities, working memory and processing speed. By contrast, the WRIT includes only the first two sets of tests, those of verbal and non-verbal ability; and so memory and processing speed tests have to be imported from elsewhere. This means that the tests in this profile are not all co-normed. However, in many cases the differences between the scores on the WRIT and the non-WRIT tests is so large that one can say with reasonable confidence that they are indicative of dyslexic difficulties.

The fact that the WRIT battery contains only verbal and non-verbal tests has given rise to a mistaken perception in some quarters that these tests are different in nature from memory and processing speed tests – and so cannot be directly compared with the latter. In fact this is not the case. All of these tests are simply cognitive tests, irrespective of whether or not they come from an IQ battery, and so they can be directly compared to give a full cognitive profile. They may together be usefully regarded as a group of tests that measure innate (or underlying) abilities – and as such they stand in contrast to tests of literacy and numeracy skills, which measure ‘surface’ or learned abilities.

And so, once IQ scores have been disregarded, a WRIT-based profile could look like this:

Source Name of test Scores
WRIT Vocabulary 118
Verbal Analogies 114
Block Design 120
Diamonds 117
Turner & Risdale Digit Memory Test(Working memory) 85
Western Psych. Services Symbol Digit Modalities Test (Processing speed) 81



1. There is strong evidence that the Verbal Analogies test may under-estimate verbal ability, particularly in the case of high-achieving clients. So, if the score on this test seems suspiciously low, use Vocabulary alone as the verbal comparator (and explain in the report why you are doing this).

2. The score on a digit span test could be misleadingly high if the client successfully uses a visual strategy to remember the digits. Always ask the client what strategy they used.

Carrying out an assessment

The process of carrying out an assessment can now be simply and briefly described:

  1. Familiarise yourself with the shapeof cognitive profiles typically found for dyslexia and other specific learning difficulties; and also for general learning difficulties. (See Appendix.) 
  2. Choose appropriate tests (verbal, non-verbal, memory, processing speed, phonology, etc.).


  1. Do not worryif some of these tests come from an IQ battery; you are not using the tests to derive IQ scores, but simply to obtain a cognitive profile. 
  2. Obtain the said cognitive profile.
  3. Analyse your results on the basis of the sub-test or (if appropriate) index scores.

Et voila!

Dr Sylvia Moody Dyslexia Assessment Service

Author of many excellent books regarding dyslexia in the workplace: http://www.amazon.co.uk/s/ref=nb_sb_noss_1?url=search-alias%3Dstripbooks&field-keywords=sylvia+moody&x=0&y=0