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Wechsler Intelligence Scale
The Wechsler intelligence scale is an intelligence test designed to test the intelligence of various age groups. It is develoiped by David Wechsler (1896-1981).
The intelligence test developed by Binet encountered problems and preferred to be an ineffective test for different age groups. The test was originally meant for children, although the Stanford-Binet edition had been adopted to test adult intelligence by adding more difficult items it was still an ineffective intelligence test for this age group.
Thus, David Wechsler, a chief psychologist at the Bellevue Hospital in New York City, developed a family of tests for people of various age groups. The tests consist of:
- The Wechsler Adult Intelligence Scale III (WAIS-III) for ages 16 to 74 (Wechsler, 1997)
- Wechsler Intelligence Scale for Children III (WISC-III) for ages 6 to 16
- The Wechsler Preschool and Primary Scales of Intelligence – Revised (WPPSI-R) is used to assess children age 4 to 61/2 (Wechsler, 1992, 1994).
Scores on these tests are calculated by comparing a person’s score with scores obtained by people from a range of ages rather than a single age. An intelligent quotient (IQ) is derived from some subtests measuring verbal and nonverbal intellectual abilities. Wechsler’s subtests can be grouped into two broad categories verbal and performance.
Verbal subtest requires an understanding of the test’s language with symbolic thought e.g. knowledge of general information, arithmetic skills, etc. In the situation where no verbal tests are applied performance tests are used. Performance tests are advantageous to people with limited verbal skills, foreigners, or poorly educated that can not follow proper instructions. These individuals achieve better results if they take the performance test and not the verbal tests.
Subtests on Wechsler Intelligence Scale
The items on the verbal and performance test are as follows:
Subtest (Verbal)
Information
Orally presented questions that tap the knowledge of common events, objects, places, and people. Sample items are, how many wings does a bird have? How many nickels make a dime?
Similarities
The examiner is asked to explain the similarity in pairs of words that are presented orally. Sample items, In what way is a lion and a tiger alike? In what way are a saw and a hammer alike?
Arithmetic
A series of arithmetic questions are to be solved without the use of pencil and paper or a calculator. Sample items, three women divided eighteen golf balls equally among themselves. How many golf balls did each person receive?
Vocabulary
The examiner must provide the definitions for a series of orally presented words. Sample items, what does near mean? What does slander mean?
Comprehension
A series of orally presented questions that require the examinee to give solutions to everyday problems or to demonstrate an understanding of social rules and concepts. Test items, What should you do if you see someone forget his book when he leaves a restaurant? What is the advantage of keeping money in the bank?
Digit Span
Number sequences are presented orally and the examinee is asked to repeat them verbatim or in reverse order. Test, I am going to say some numbers. Listen carefully and when I am through you say them right after me: 2,4,7. Repeat these numbers backward 4,6,1,7,5.
Subtest (Performance)
Picture Completion
The examiner is asked to identify the important part that is missing in each of a set of colorful pictures of common objects and themes. Sample, Look at this picture. What important part is missing?
Digit-Symbol Coding
Each of a series of shapes or numbers is paired with a simple symbol, based on a key, the examinee draws the symbol under the corresponding number. Test, look carefully at the key that matches numbers with symbols. Then write the number that goes with each symbol in the space below it.
Picture Arrangement
A set of colorful pictures is presented out of order, and the examinee rearranges them in a logical story sequence. Arrange the pictures on these cards so they tell a story that makes sense.
Block Design
The examinee uses two-color blocks to replicate a design from a model or a picture. Test, arrange the blocks so they look like the design in the picture.
Symbol Search
The examinee scans two groups of symbols and a search group of 5 symbols and indicates whether either target symbol matches any symbols in the search groups.
Wechsler test is an individual test in which only one person can be tested at a time. Wechsler tests provide an overall IQ score, and a separate score for each of the 14 subtests, as well as yielding overall scores for verbal and performance IQ. The advancements in neuroscience are making these tests more cognitively important in intellectual aspects.
Wechsler’s intelligence test is also time-consuming like the Binet test, taking about 1 to 2 hours to finish the test. The Wechsler test too needs to be administered by a skilled professional. These tests have several benefits, while administrating tests the examiner can assess the test takers’ strengths, weaknesses, emotions, and other problematic areas. Wechsler’s test also helps to differentiate different problems in children including learning disabilities.
Wechsler in his intelligence scale developed the deviation IQ which is now widely used in well-standardized intelligence tests. The deviation IQ is taken from the standard deviation, which indicates the number of the scores derived from the average or means. A large deviation or variability indicates that many scores deviate more and a small standard deviation shows less variability. This method allows any individual’s score to express in terms of how it compares to the standard deviation. The deviation IQ is a standard score in which the IQ is expressed in standard deviation units. Wechsler tests have three different deviations IQ, one for the verbal subtests, another for the performance subtests, and a third full-scale IQ. Where, X = Individual score, M = Mean score, and SD = Standard deviation.
Deviation IQ can be expressed in the formula: Standard Score = X-M/SD
Suppose in a psychological test your score is 80, and the mean score of your peers is 70, and the standard deviation is 10 (80-70/10=1). The answer to your deviation IQ is 1. Likewise, in a second class test, you received an 80 again. The mean is 70, but the standard deviation is 15, making your deviation IQ (80-70/15=0.67). In the first case, a score of 80 was equal to +1 standard deviation unit above the mean and 0.67 standard deviations above the mean on the second test. Wechsler converted the standard score to 100 and the actual standard deviation to 15. The test makers of Scholastic Assessment est (SAT) make the mean score 500 and standard deviation equal to 100. In that case, the first test score would be converted to 600 and the second to 567.