The most widely-used IQ tests are the Wechsler, the Stanford-Binet and the Raven’s Progressive Matrices tests.
Wechsler (WAIS IV)
In 1955, American psychologist David Wechsler published a new intelligence test that became known as the Wechsler Adult Intelligence Scale (WAIS). He defined intelligence as “the global capacity of a person to act purposefully, to think rationally, and to deal effectively with his environment.” To measure this faculty, he created two sub-tests: one measuring “verbal intelligence” and the other, “non-verbal (performance) intelligence”. Assuming that intelligence is normally distributed, Wechsler mapped his test scale onto a normal distribution with mean 100 and standard deviation 15. By standardizing his tests in this way, Wechsler linked his scale directly to percentiles, allowing for immediate comparisons to average intelligence.
Wechsler’s departure from a single measure of intelligence offered by the Stanford-Binet test evolved from his recognition that intelligence may have more than one dimension. Growing recognition of these multiple dimensions led to subsequent revisions of the Wechsler tests to include measures of verbal comprehension, perceptional reasoning, working memory, and processing speed. WAIS-IV, the fourth edition of the Wechsler tests, released by Pearson in 2008, has 10 subtests and 5 supplemental tests that summarize intelligence with two measures–a final IQ score and a General Ability Index, along with scores on the four dimensions described above It is the most widely-used test for adolescents and adults.
Raven’s Progressive Matrices
The multiple-choice format was used in the WAIS tests to simplify as well as standardize the scoring, by removing human judgment of answers as a variable. Despite this, however, some items involving vocabulary were criticized as culturally dependent, because people from educationally deprived environments may not have been exposed to an expansive vocabulary. To address this criticism, psychologist John Raven developed multiple choice tests known as the Raven’s Progressive Matrices. Items in these tests were language-free and required the recognition in patterns of change across a display of visual elements. An example of such a test item can be seen at: https://www.intelligence-and-iq.com/how-does-an-iq-test-measure-reasoning-skills/
Each test consists of either 48 or 60 items, presented in order of increasing difficulty and is time-limited to about 40 minutes. Answering an item correctly involves choosing the matrix or matrices that complete the pattern or patterns evident within the progression from left to right and/or top to bottom.
In 2008, the Psychometrics Centre at the University of Cambridge was awarded a contract from Pearson Assessment to undertake the standardisation of the Ravens Progressive Matrices and Vocabulary Scales throughout the United Kingdom. This lead to the publication of the Raven’s Educational versions of the SPM+ and the MHV, as well as the CPM and CVS scales described below.
The Raven’s Progressive Matrices tests come in 2 formats:
- Coloured Progressive Matrices (CPM) (for use with children under 8 and elderly people)
- Standard Progressive Matrices (SPM) (for use with children of 8 and above as well as the general population)
The vocabulary scales associated with these tests measure the ability to store, process and apply information and knowledge particular to a given culture. They are the:
- Crichton Vocabulary Scale (CVS) (for use with the CPM)
- Mill Hill Vocabulary Scale (MHV) (for use with SPM)
Commercial books and on-line IQ tests containing items similar to the WAIS IV and Raven’s Progressive Matrices are available, but these are not generally normed across a large population using appropriate statistical techniques to guarantee IQ accuracy. However, they can be very useful in practising for a formal IQ test. To achieve a reasonably accurate measure of your IQ you should have a test administered by a trained psychometrician under proper supervision.
