Definition:  Tests designed to measure intelligence or other constructs related to cognitive ability.

       Description.   The ambiguous definition above reflects the longstanding uncertainty about what traditional intelligence tests measure. Sternberg (1984) summarized the beliefs of many when he wrote that although many psychologists “act as though ‘intelligence is what intelligence tests measure’…few of us believe it” (p. 307).  Measures of cognitive abilities can predict educational and occupational performance and are associated with health and mating choices (Plomin & Deary, 2015). What these tests measure, however, remains in some doubt. On the basis of strong positive correlations among intelligence measures, Spearman introduced the idea of g, or a general factor of intelligence. Subsequent work by Thurstone (1938) and Guilford (1967) indicated that more specific group factors accounted for the operation of cognitive abilities.  Ascertaining the structure of cognitive abilities remains an important but elusive goal for those who desire to improve the measurement of cognitive abilities and skills.

Three related types of tests are:  (a) achievement tests, intended to measure students’ current academic skills and accomplishments, (b) ability tests, broad tests of skills intended to estimate general intellectual ability, and (c) aptitude tests, tests designed to measure specific skills, independent of previous learning, in the hope of predicting future performance in that domain.  While often described as distinct types of cognitive ability tests, achievement and ability tests correlate highly.  Ability or intelligence tests typically tap into verbal comprehension, reasoning, and perceptual organization; aptitude tests focus on one of these specific areas.

While many achievement and aptitude tests are administered in groups, ability tests such as the Wechsler tests of general intelligence–the Wechsler Adult Intelligence Scale-Revised (WAIS-R) and the Wechsler Intelligence Scale for Children (WISC-III)–are individually administered.  Both tests consist of a battery of tasks that produce a verbal, performance, and full scale IQ scores.  Tasks include arithmetic, vocabulary, picture arrangement, object assembly, and comprehension. Reviews of the WAIS typically find high reliability; full scale WAIS scores have been found to correlate highly with other intelligence measures as well as with years of education.

Here is an excellent video about the WAIS-IV.