Individual Differences

Intelligence

Wechsler Adult Intelligence Scale (WAIS)

Last updated:
13 Apr 2004

Brief information about the Wechsler Adult Intelligence Scale

WAIS Scales

Interpretation of the WAIS-R

Discussion question

More detailed notes about the WAIS-R

WAIS-R psychometrics (reliability & validity)

Brief information about the Wechsler Adult Intelligence Scale

  • David Wechsler designed intelligence tests made up of items that are appropriate for a wide range of ages.

  • There are three main types of Wechsler intelligence tests:

    • Wechsler Pre-school and Primary Scale of Intelligence (WPPSI) - 3-7 years

    • Wechsler Intelligence scale for Children (WISC) - 7-16 years

    • Wechsler Adult Intelligence Scale (WAIS) - 16 years and over

  • The first was the Wechsler-Bellevue Intelligence Scale (Wechsler, 1939).

  • Replaced 1955 by the Wechsler Adult Intelligence Scale (WAIS).

  • 1981 revision is referred to as the WAIS-R.

  • A subsequent revision was conducted in the US in 1997 and the present scale is the 3rd edition, known as the WAIS-III.  The revised version has almost 80 per cent of the original form. A number of improvements have been made including an attempt to make it more culturally fair.

  • The WAIS(R) was standardised on a sample of 1,800 U.S. subjects, ranging from 16 to 74 years of age. It was a highly stratified sample, broken down into 9 different age groups. Equal numbers of men and women were used, as were white and non­white subjects, in line with census figures. It was further broken down into four geographic U.S. regions and six occupational categories. There was also an attempt to balance urban and rural subjects. The mean I.Q. for each age group on this test is 100, with a standard deviation of 15. The WAIS scales have impressive reliability and validity.

  • There are different adaptations of the scale by country.  For example, in Australia we have the Australian adaptation of the WAIS-R (1989). 

  • 11 separate subtests, which are broken into the Verbal scale (6 subtests) and the Performance scale (5 subtests). 

  • A person taking the test receives a full-scale IQ score, a verbal IQ score, a performance IQ score, as well as scaled scores on each of the subtests.

WAIS Scales

  • Verbal WAIS scales

1. Information: 29 questions - a measure of general knowledge.

2. Digit Span: Subjects are given sets of digits to repeat initially forwards then backwards. This is a test of immediate auditory recall and freedom from distraction.

3. Vocabulary: Define 35 words. A measure of expressive word knowledge. It correlates very highly with Full Scale IQ

4. Arithmetic: 14 mental arithmetic brief story type problems. tests distractibility as well as numerical reasoning.

5. Comprehension: 16 questions which focus on issues of social awareness.

6. Similarities: A measure of concept formation. Subjects are asked to say how two seemingly dissimilar items might in fact be similar.

  • Performance WAIS scales

7. Picture Completion: 20 small pictures that all have one vital detail missing. A test of attention to fine detail.

8. Picture Arrangement: 10 sets of small pictures, where the subject is required to arrange them into a logical sequence.

9. Block Design: Involves putting sets of blocks together to match patterns
on cards.

10. Digit Symbol: Involves copying a coding pattern.

11. Object Assembly: Four small jig-saw type puzzles.

Interpretation of the WAIS (R)

  • Three IQ scores are obtained from the WAIS(R):
    1. Verbal IQ
    2. Performance IQ
    3. Full Scale IQ

  • Interpretation is fairly systematic and can be broken down into a number of discrete steps:

1. Obtain the 3 IQ scores. What standardized categories do they fall into?

2. Is there a Verbal-Performance discrepancy? Is it significant?

3. Break WAIS scores down into the factorial sub-structure:

(a) Verbal Comprehension

(b) Spatial Perceptual

(c) Freedom from Distraction

  • Are individual sub-tests very low or very high? why?

  • What is the degree of intra-subtest scatter?

Discussion question

  • Do you believe that this type of test is tapping "intelligence"

More detailed notes about the WAIS-R

“Intelligence is multifaceted as well as multidetermined…What it always calls for is not a particular ability but an overall competency or global capacity” (1981, p. 8). So speaks David Wechsler writing in 1981.  The WAIS-R is an individual test of intelligence, was a revision of the original Wechsler-Bellvue Scale created in 1939 and updated in 1955.  This revision has subsequently been updated in 1997 but I’ll talk about this one as it’s the one referred to in tutes this week and is very similar to the 1997 revision.

According to Wechsler, intelligence is influenced by personality traits and other nonintellective components, such as anxiety, persistence and goal awareness. These nonintellective factors are important,  according to Wechsler, but he remarks ”no amount of drive will develop a dullard into a mathematician” (1981, p.8).

The WAIS-R gives a global IQ and also two separate IQ’s for the two scales: verbal and performance.  There are 6 verbal subscales and 5 performance subscales. Wechsler believes that this test is a good measure of “g”. The two scales can be used separately to see if a person has particular strengths or weaknesses. Wechsler suggests that if there is more than 15 IQ points difference between the two main scales then this might be cause for further investigation. The design of the test, with the two scales, means that the verbal & performance scales can be used alone. The Performance section alone can be used with examinees who are unable to properly comprehend or manage language, or the Verbal scale alone can be used with examinees who are visually or motor impaired. There is little emphasis on speed in this test with only some subscales having time limits and some subscales having bonuses for speed.

WAIS-R Psychometrics

So what are some of the psychometric properties of the test? Well firstly a large standardization sample was used of 1880 Americans. This sample was 50% male and 50% female. The individuals who formed the standardization sample were aged from 16 years 0 months to 74 years 11 months.  The standardization sample was highly representative of the US population in terms of age, sex, race, geographic region, occupation, education and urban-rural residence. The individuals in the standardization sample were tested between Nay 1975 and May 1980 at 115 testing centres across the U.S.

The scaled scores were based on a reference group of 500 subjects in the standardization sample aged between 20 and 34. Although scaled scores for each of the 11 subtests are obtained using a single table based on the reference group, IQs are derived separately for each of the age groups (there are nine e.g. 16-17, 18-19, 20-24, 25-34….70-74).

The test can be used for people aged 16 and up. It has found to be appropriate for use with those over 74.

So the WAIS has a good standardization sample and it is also considered to be reliable and valid.

The reliability coefficients: (internal consistency) are .93 for the Performance IQ averaged across all age groups and .97 for the Verbal IQ, with an r of .97 for the full scale. Reliability for the 11 substests is not as strong.

Split half reliability:    .95+  (very strong)

Evidence supports the validity of test as a measure of global intelligence.  It does seem to measure what it intends to measure. It is correlated highly with other IQ tests (e.g. The Stanford-Binet), it correlates highly with empirical judgements of intelligence; it is significantly correlated with a number of criteria of academic and life success, including college grades, measures of work performance and occupational level.  There are also significant correlations with measures of institutional progress among the mentally retarded.

One concern we discussed in some of my tutorials was with reference to the comprehension subscale on the Verbal Scale. Was a question such as “What is the thing to do if you find an envelope in the street that is sealed and addressed and has a new stamp?” a valid measure of intelligence. The only fully correct response to that question (i.e. score of 2 is if you mail it or return it the post-office or a postman. You get one point if you recognise it belongs to someone else and try to give it to say a policeman and you get 0 points if you suggest opening it, which frankly is not morally correct in our society but may be a clever thing to do especially if you see some cash in it! So it’s a culturally and morally loaded question. The topic of culture-fair tests is a topic we’ll consider in the tutes this week.