Ability tests are assessment instruments designed to measure the capacity of individuals to perform particular physical or mental tasks. Ability tests were developed in the individual differences tradition of psychology and evolved from early tests of general intelligence. Most major ability tests assess a range of broad ability factors that are conceptually and empirically related to general intelligence (or g, also referred to as general cognitive ability). Ability tests are frequently used in settings such as schools, military organizations, business and industry, hospitals and rehabilitation centers, and private practice. Several ability tests with strong evidence of reliability and validity are currently available and are commonly used for purposes such as educational screening or diagnosis, personnel selection and classification, neuropsychological assessment, and career guidance and counseling.

The first successful "mental test," predecessor to all subsequent tests of characteristics of individual differences characteristics (including ability), is generally considered to be the intelligence test developed by French psychologist Alfred Binet and his associate, Théodore Simon. First published in 1905, the Binet-Simon Intelligence Scale was designed to identify children presumably unable to benefit from regular classroom instruction by measuring their ability to judge, understand, and reason. The test was found to be an effective predictor of scholastic achievement. The success of the Binet-Simon scales and of later measures, such as Lewis M. Terman's Stanford-Binet Intelligence Scale (published in 1916), led the emerging testing industry to focus on the further development of intelligence measures. Many of these early intelligence tests actually measured a range of different abilities.

At the outset of World War I, leading psychologists in the intelligence testing movement began attending to the problem of selecting and classifying recruits for the United States military. These efforts resulted in the development of group-administered intelligence tests such as the Army Alpha and Beta. The practical usefulness of these assessments and the efficiency with which they could be administered to large numbers of people led to the widespread use of tests and also to intensified research on specific areas of ability relevant to success in a variety of contexts. During the 1920s and 1930s, this shift from measures of general Page 2  |  Top of Article intelligence to measures of specific abilities was accompanied by the development of a Statistical technique called factor analysis. By identifying underlying factors on the basis of patterns of intercorrelations among a large number of variables, factor analysis made it possible to demonstrate that specific abilities (e.g., reading speed, reaction time) are indicators of broad areas of ability (e.g., broad visual perception, broad cognitive speediness) and that these broad abilities are somewhat independent of g.

Largely on the basis of evidence obtained from early factor analytic studies, two opposing theoretical approaches to understanding the ability domain emerged. The London school, led by Charles Spearman, emphasized g as the single most important ability. In contrast, a group of American scientists, led by Truman Kelley and Louis L. Thurstone, identified several relatively independent, broad ability factors. A classic study of mechanical ability, led by D. G. Paterson, provided early empirical evidence to support the claim that general areas of ability other than g accounted for significant variance in practical outcomes, such as job performance.

With World War II came the demand for follow-up efforts to the work conducted in the 1920s and 1930s. During the 1940s and 1950s, general multiple-ability test batteries, such as the Differential Aptitude Tests (DAT) and General Aptitude Test Battery (GATB), among many others, were developed and used frequently in subsequent decades. During the 1980s, controversy erupted over the question of fair use of the GATB, which was developed by the United States Employment Service, with prospective employees from racial and ethnic minorities. This controversy led to its suspension from use pending further study. A variety of alternative test batteries (three of which are reviewed below) measuring multiple areas of ability are available and in use today.

The construct of ability, as defined above, refers to the power of an individual to perform a specified act or task. Abilities are generally assumed to be fairly stable, to have a biological basis, and to be both learned and innate. Ability may be differentiated from related constructs, such as achievement, which is defined as the level of knowledge or skill that has already been attained in an endeavor; aptitude, which is defined as the capacity to develop particular knowledge or skills in the future; and intelligence, which is typically defined as a general, higher-order ability relevant to tasks that have cognitive demands. These constructs clearly are related, and in practice the terms are sometimes used interchangeably. To further complicate the matter, tests of abilities or intelligence technically measure achievement and usually are used to infer aptitude. In the context of assessment, a general rule of thumb is as follows: achievement tests typically are designed to measure knowledge of a specified content area that has been explicitly taught; ability tests typically are designed to measure current performance in a particular content area or, when composed of a battery of subtests, across multiple content areas; and intelligence tests typically are designed to measure general cognitive ability. All three are used to infer aptitude, although the terms aptitude tests and multiaptitude tests usually refer to tests of ability.

There are a variety of theoretical approaches to understanding human ability, but the view most commonly held by scholars is that the domain of abilities can be represented using a hierarchical structure. For example, the Cattell-Horn-Carroll (CHC) theory of cognitive abilities, supported by one of the most comprehensive factor-analytic investigations of abilities in history, posits a three-level hierarchy. Like many hierarchical theories of abilities, CHC theory places g at the highest level, followed by several broad factors at the intermediate level of specificity and, in turn, by a large number of more narrowly defined, specific abilities at the lowest level (in the CHC model, these are approximately 70 in number). The 10 broad ability factors in the second level of the CHC model are similar to those posited by other hierarchical ability models and are as follows:

The preceding list of broad abilities in the CHC model is generally representative of the ability factors traditionally targeted for measurement by multiaptitude test batteries, although some differences exist across competing models of ability and measures of the domain. For example, because the CHC model targets cognitive ability, some abilities that are not traditionally considered cognitive in nature (e.g., psychomotor dexterity) and that are integral parts of other models of ability are excluded from the list. Also, some scholars have called for an expanded view of abilities that may include, for example, emotional intelligence, social intelligence, situational judgment, and other areas of human performance not typically included in traditional theoretical models of the ability domain.

Although the specific features of various theoretical models underlying particular ability tests may differ, most major ability tests assume the following: (a) There are multiple abilities that can be reliably and validly measured using a single, wide-range test or battery; (b) there are differences between people in terms of level of performance in each area of ability; (c) there are differences within people in terms of level of performance across different areas of ability; (d) differences between a person's level of abilities relative to a normative group, and differences within a person's pattern of ability scores, predict real-world outcomes (e.g., academic and occupational performance); and thus (e) scores from ability tests offer useful information in settings where decisions related to education, employment, and rehabilitation are made. It should also be noted that ability tests measure maximal performance; some have proposed that typical performance may better predict some real-world outcomes.

Several multiaptitude test batteries are currently available. Users are encouraged to select an instrument according to such criteria as the evidence for reliability and validity; the appropriateness of the normative samples used to standardize the test; the ease with which the test can be obtained, administered, and scored; the extent to which scale scores provide clear, unambiguous results; and the extent to which proposed applications of the test coincide with the needs of the user. The following are brief descriptions of three commonly used multiaptitude test batteries.

The Armed Services Vocational Aptitude Battery (ASVAB; U.S. Department of Defense) is best known for its use in military selection and classification and for its inclusion as part of a comprehensive career exploration program for high school and college students. The ASVAB consists of the following subtests, each separately timed: General Science, Arithmetic Reasoning, Word Knowledge, Paragraph Page 4  |  Top of Article Comprehension, Numerical Operations, Coding Speed, Auto and Shop Information, Mathematical Knowledge, Mechanical Comprehension, and Electronics Information. Factor analytic evidence suggests that the ASVAB measures general cognitive ability, verbal-math ability, clerical speed, and technical knowledge. The ASVAB was developed using impressive norms, but its usefulness for differential prediction has been questioned.

The Occupational Information Network (O*NET) Ability Profiler (published by the U.S. Department of Labor) is a component of the O*NET Career Exploration Tools system. The O*NET Ability Profiler is an updated version of the GATB and is available in paper-and-pencil format with optional apparatus subtests. The O*NET Ability Profiler consists of 11 subtests that measure nine job-related abilities: verbal ability, arithmetic reasoning, computation, spatial ability, form perception, clerical perception, motor coordination, manual dexterity, and finger dexterity. A major strength of the battery is that it generates a computer-generated score report that can be linked to a wealth of occupational data in the O*NET database, allowing individuals to, for example, compare their pattern of abilities to those required by different occupations.

The DAT, published by the Psychological Corporation, was designed primarily for educational and career guidance of individuals in middle school, high school, and adulthood. The DAT provides scores for the following eight areas of ability: verbal reasoning, numerical ability, abstract reasoning, perceptual speed and accuracy, mechanical reasoning, space relations, spelling, and language usage. The DAT scores are computed using very good norm groups, and efforts to address test fairness have been thorough. Evidence supporting the reliability of the DAT scores is strong, although relatively little evidence is available to assess the validity of the scale scores for predicting outcomes other than academic achievement.

Each of the preceding test batteries has garnered evidence of reliability and validity, and this evidence is reviewed in the user's manuals. As indicated in their descriptions, the ASVAB, O*NET Ability Profiler, and DAT typically are used for educational and vocational counseling and personnel selection. Other purposes for testing abilities, such as neuropsychological evaluation or educational diagnosis, naturally require tests with validity evidence supporting their use for those purposes.

As is the case with any test, users must be sensitive to the ways in which personal or group characteristics such as age, gender, ethnicity, linguistic background, disability status, and educational and work history may influence performance on ability tests. Although the weight of evidence suggests no difference between females and males in general cognitive ability, consistent differences have been found favoring females on tests of some verbal abilities and males on tests of some visual-spatial tasks. Evidence also suggests that scores on quantitative abilities tend to favor females in the early years of school and males from adolescence onward. Most scholars suggest that biological and social factors work in tandem to produce such differences.

Some differences between ethnic groups have been found in scores on tests of ability. This finding contributed to the previously noted controversy over the GATB, for example. The crux of the controversy was that some minority groups tended to score lower than the majority on some GATB subscales and, since the U.S. Department of Labor had suggested that states use the test as part of a new employment selection system, members of these groups were adversely impacted. However, scores on the GATB (and other tests of ability) tended to predict educational and occupational outcomes equally well, regardless of ethnicity. Eventually the use of within-group norms in employee selection was proposed, but this suggestion was also controversial, and as mentioned earlier, the GATB was eventually suspended from use. Because Page 5  |  Top of Article many tests measure abilities that are influenced by education and training, users must take into account the quality of the respondent's educational background. This is particularly important when interpreting scores of ethnically diverse respondents because minority groups are more likely than members of the majority to be socioeconomically disadvantaged, which in turn is related to poorer school systems and fewer educational opportunities that might improve test performance. Of course, it bears remembering that within-group differences are larger than between-group differences and that meaningful generalizations from the group to the individual can never be made responsibly without additional information.

Ability tests allow users to identify current and potential performance strengths for individuals, information that is useful for a wide range of purposes in a variety of contexts. Many ability tests are laden with positive features that likely contribute to their widespread use, such as ease of administration and scoring, strong psychometric evidence, and the provision of a large amount of meaningful information in a relatively brief period of time. With recent advances in technology, ability testing has become increasingly automated, and in the future, computer-administered testing will continue to improve convenience of use and also will allow users to customize their batteries to better suit their specific needs. When combined with other sources of information, the potential benefits of ability tests to individuals and society are substantial.