Wechsler Scale:
This scale may be considered as an improvement over Binet-Simon scale as it can measure the intelligence
This scale was developed in two equivalent forms and each form consisted of ten sub-tests of which five tests were verbal and five non-verbal or performance type.
This scale was revised in 1955 and renamed Wechsler Adult Intelligence Scale (WAIS). It comprised of 11 sub-tests of which 6 were verbal and 5 were non-verbal. This scale is used in persons above 16 years of age up to 64 and administration time of the scale is 1 hour. The details of these 11 sub-tests are given below:
1. Verbal Sub-Tests
i. Information: A total of 29 questions are given here to test the recall of knowledge concerning wide varieties of information.
ii. Comprehension: A total of 14 questions are given here to test the understanding of knowledge concerning a particular subject of events.
iii. Arithmetic: A total of 14 questions are given here to test numerical ability. These questions are solved orally without paper and pencil at all.
iv. Similarity: A total of 13 questions are given here to measure abstract verbal reasoning. Examinees are required here to compare two objects and find out the relationship between them.
v. Digit Span: Memory of digits is measured here. In the first half, the examinee is asked to repeat three to nine digits presented in forward directions in the same order and in the second half, the digits are repeated in backward direction.
vi. Vocabulary: In this test, a total of 40 words of increasing difficulty value are presented before the examinees and they are asked to tell the meaning of these words.
2. Non-Verbal or Performance Sub Tests:
i. Digital Symbol: Nine digits each with different symbols are given to the examinees here and they are asked to give the right side for each digit or symbols.
ii. Picture Completion: This sub-test measures the ability of the examinee to analyse the parts from the whole. Examinees are given 21 cards containing incomplete pictures and they are asked to fill the missing parts of each picture.
iii. Block Design: Its purpose is to measure the ability to analyse the complex whole. There are only seven designs in these blocks which have red, white, and red-white sides. Examinees are asked to produce a given design with the help of these blocks.
iv. Picture Arrangement: Its purpose is to measure the ability to identify the whole from the parts. Here, six sets of pictures are given to the examinees and they are asked to arrange them in order which tells a meaningful story.
v. Object Assembly: Its purpose is to measure the ability to synthesize the whole with the help of parts. Here, examinees are given some puzzle pictures where each represents some parts of the human body. They are then asked to assemble them in the form of a complete man.
Speed and accuracy factors are also scored in arithmetic, digital symbol, block design, picture arrangement, and object assembly. Raw scores of each subject are converted into normalized standard scores with a mean of 10 and standard deviation (SD) of 3. This makes the scores of each subtests comparable. Separate IQ for verbal and nonverbal subtest forms is calculated by adding up the respective sub-tests of the two forms. If we add up the scores on all the 11 sub-tests, we obtain the total score. These standard scores are expressed in the form of deviation IQ with a mean of 100 and SD of 15.
Wechsler developed another scale known as Wechsler Intelligence Scale for Children (WISC) in 1949 to test the intelligence of children from 5 to 15 years of age. Although there are 12 sub-tests in this scale, it also takes only 1 hour to administer. A maze subtest has eight mazes to be traced by the examinee with a pencil. These mazes are given in order of increasing difficulty.
The scoring system of both the tests (WAIS and WISC) is the same. Here also the scores are converted into deviation IQ with a mean of 100 and an SD of 15.
Advantages of Wechsler Scale:
1. Although both Binet's scale and Wechsler's scale are individual scales, the later can be administered on small groups of children and adults.
2. Wechsler scale is easier to administer than Binet's scale and its scoring is also less complex than former.
3. Wechsler has prepared separate scales for children and adults, while Binet's scale does not possess this advantage.
Other Differences of Wechsler Scales and Stanford-Binet (SB) Scale:
1. In Wechsler scale, items are not grouped in terms of mental age as is the case with SB scale. Points are given here for all the correct responses. Thus, WAIS or WISC is a point scale.
2. In SB scale, items are interpreted in terms of different age levels of examinees but in WAIS or WISC, similar types of items are grouped together to form sub-tests.
3. WAIS has separate age norms for adults, but in SB scale all the individuals above 18 are treated in a similar manner as far as computation of IQ is concerned. Thus, people of all age levels are treated as 18 years of age after 18.
4. In SB test are varied, unrelated and upgraded but in WAIS and WISC tests, items are graded according to various ranges of ages.
5. SB scale is internally standardized and rigid, but WAIS is externally standardized and flexible.
6. SB scale refers to qualitative evaluation, while WAIS refers to quantitative evaluation
7. Slight chance of statistical treatment is possible in SB scale, but WAIS is fully subject to all statistical analysis.
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