Many psychologists define intelligence as a capacity learned from experience and to adapt successfully to one's environment.
The Stanford-Binet is an intelligence test that yields an intelligence quotient (IQ): mental age divided by chronological age and multiplied by 100. Today, an IQ represents a person's performance relative to the average of same-age peers.
The Wechsler Adult Intelligence Scale (WAIS) distinguishes between different aspects of intelligence by producing separate verbal and performance scores. Wechsler scales also are available for children.
The SAT and ACT are examples of group aptitude tests. These tests attempt to make a distinction between aptitude and achievement but the two factors are difficult to separate.
For the sake of accuracy, an intelligence test must be standardized, reliable, and valid. Standardization means that the test provides a standard of norms than can be used to interpret a given score. Reliability means that the test yields consistent results. Two types of reliability exist: test-retest reliability and split-half reliability. The extent to which the test measures or predicts what it is supposed to assess and predict is called validity. There are two types of validity with regard to intelligence testing. Content validity is concerned with whether test questions adequately measure intelligence. Criterion validity refers to whether the results of intelligence tests predict academic achievement. These tests correlate highly with grades in school but are less predictive of how well people adapt to real-world circumstances.
It has been argued that intelligence tests are culturally biased because scores are influenced by such background factors as the test taker's racial or ethnic group. In response to this, advocates of testing note that ethnic differences occur even on "culture-fair" items and that intelligence tests do predict academic performance.
The Nature of Intelligence
General intelligence (g) is a broad factor underlying all mental abilities. With the use of factor analysis, a statistical technique used to identify clusters of test items that correlate with one another, Spearman found that all intellectual abilities are linked to g. There is some support for the general intelligence factor. Others in this field divide intelligence into various components.
Gardner proposed a theory of multiple intelligences. According to Gardner, different areas in the brain produce seven different types of intelligence: linguistic, logical-mathematical, spatial, musical, bodily-kinesthetic, interpersonal, and intrapersonal.
According to Sternberg's triarchic theory of intelligence, there are three basic types of intelligence. Analytic intelligence is the kind of skill shown on traditional IQ tests and by academic grades. Creativity refers to the mental processes that lead to unique and novel ideas or objects. One key to creative insight is divergent thinking, the ability to think flexibly and entertain a wide range of possible solutions. Practical intelligence is the ability to size up situations and adapt to real-life demands. This ability involves social competence, wisdom, and emotional intelligence.
The Great Debates
People disagree about the extent to which intelligence is determined by nature (genetics) and by nurture (environment). There is evidence that supports both sides of this debate. Studies of twins do show a hereditary influence on intelligence but social programs can have a measurable effect on IQ and academic success.
Girls score somewhat higher on verbal tests but boys perform better on mathematical and visual-spatial tasks. Both biological and social explanations are offered to explain these gender differences.
Gifted children do well in later life. Today, many children identified as gifted are offered special programs, which do benefit them. Individualized education programs assist students with different levels of mental retardation. However, reliance on test results may lead educators to underestimate a child's ability. According to studies of the self-fulfilling prophecy, teacher expectations influence student performance. If teachers expect that a child will not succeed academically based on a low IQ score, that child will likely perform accordingly. Recent studies of stereotype threat also indicate that social and cultural groups feel threatened by negative stereotypes about them. This threat makes them anxious and impairs their performance. Regarding tracking students, today most educators favor flexible within-classroom grouping policies.