The relationship between intelligence and crime remains a fiercely debated topic. Despite recent advancements through revised intelligence tests and sophisticated brain imaging techniques, there remain numerous theoretical deficiencies regarding the mechanisms underlying the intelligence – crime relationship. Needless to say, these short comings need to be examined more thoroughly, and new hypotheses must emerge, before the role of intelligence in criminal behavior can be fully explained.
II. What Is Intelligence?
III. How Is Intelligence Measured?
VIII. Intelligence and Interventions
Intelligence is the most studied human characteristic in the world. Since World War I, millions of individuals across virtually every continent have taken intelligence tests. The information garnered from these tests has been subject to intense debate over the validity of the results and the interpretation of the patterns found. IQ (intelligence quotient, a score on any of several standardized tests), it seems, is an important predictor of life outcomes, such as the level of education one achieves and the amount of money a person will earn over his or her lifetime. IQ, however, is also linked to a number of social problems. IQ predicts the use of welfare and other social safety nets. It predicts the number of births one will have out of wedlock and, more important, it predicts criminal involvement. For these reasons, and more, it is fair to say that no other variable has generated as much debate or as much criticism as has IQ.
II. What Is Intelligence?
Definitions of human intelligence generally point to at least three characteristics. First, intelligence is best understood as a compilation of brain-based cognitive abilities. According to 52 eminent intelligence researchers, intelligence reflects “a very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience” (Ellis & Walsh, 2003, p. 343).
Intelligence comprises a multidimensional set of cognitive abilities that allow an individual to cognitively assess complex situations, use reason and logic to solve problems, and formulate adaptive behavioral responses to environmental situations and alter those responses when necessary. The collection of abilities that fall under the umbrella of “intelligence” provide an individual the ability to learn, to learn from mistakes, and to recall situations in which mistakes were made so that they will not be made again. In short, intelligence reflects a range of cognitive abilities, not just a single ability.
Second, IQ reflects the intercorrelations between these brain-based abilities. Virtually all studies find that the unique abilities that compose intelligence have a strong tendency to correlate with each other (Ellis & Walsh, 2003). Individuals who score high on measures of specific mental abilities, such as spatial visualization, are also more likely to score high on measures of other mental abilities. For example, people who are capable of using reason to solve problems are also more likely to be able to plan for the future, to seek out and to acquire information to make better informed decisions, and to be able to use that information to their advantage.
Third and finally, general intellectual abilities are hierarchical. Because unique intellectual abilities correlate strongly with a diverse array of other intellectual abilities, their patterns of correlations can be subsumed under a broad, overall quantitative assessment of general intelligence. This quantitative assessment is referred to as g.
To understand the hierarchical nature of g, think of a professional athlete. The qualities that compose professional athletes are multidimensional. Many athletes are physically strong, can endure tremendous amounts of physical stress, and are highly competitive. These components are usually visible in the best athletes—that is, these athletic abilities correlate. Now, if we wished to assess an athlete’s overall level of athleticism, we could score the athlete on each of the dimensions that compose our measure of athleticism and create an overall score. Psychologists do much the same to measure g.
III. How Is Intelligence Measured?
A range of intelligence tests have been created and intensively analyzed. Some of the better-known intelligence tests are the Stanford–Binet (e.g., Roid, 2005), the Wechsler Intelligence Scale for Children (e.g., Wechsler, 2003), the Wechsler Adult Intelligence Scale–Third Edition (Wechsler, 1997), the Wechsler Preschool and Primary Scale of Intelligence–Third Edition (Wechsler, 2002), and the KaufmanAssessment Battery for Children (Kaufman & Kaufman, 2002).
These tests have been found to meet the criteria for scientific acceptance. They have high test–retest reliability, and they predict important life outcomes (i.e., they have construct validity). They also appear to be valid indicators of an individual’s overall level of intellect. No critical assessement of contemporary IQ tests has yet revealed substantial bias, and no critical assessement of these tests have proven them to be invalid measures of cognitive abilities.
To aid in comparing scores on IQ tests, scientists statistically norm the tests. Doing this allows individual scores to be compared with others’ scores and ranked accordingly. Because of the norming of the tests, the distribution of g follows the mathematical properties of a normal curve. Under a normal curve, which resembles the shape of a bell, scientists can easily compute the proportion of individuals with a specific IQ. For example, intelligence tests have a mean (average) of 100 and a standard deviation of 15 points. Between ±1 standard deviations (85–115 IQ points) falls slightly over 68% of the population; ±2 standard deviations (70–130 IQ points) encompasses 95% of the population.