Although people may give a reasonable description of intelligent behavior, psychologists have difficulty formally defining intelligence.

1. What is intelligence?
   Is intelligence a general characteristic that appears in many behaviors and activities, or does it consist of separate skills and abilities? Should intelligence be conceptualized in terms of the products that arise from people's activities (emphasized by the psychometric approach) or in terms of the processes people use to solve problems (emphasized by the learning and information-processing approaches)?
   1. Psychometric approaches
      Alfred Binet and Théophilius Simon developed the first formal intelligence test and thus established the psychometric model of intelligence. Psychometric models test large numbers of individuals to quantify and rank-order individual differences in abilities. Charles Spearman's two-factor theory emphasized a general (or global) intelligence factor that is involved in any cognitive task, although he did acknowledge more specific knowledge and abilities as well. Louis Thurstone believed that intelligence is composed of seven independent mental abilities rather than one general factor. J. P. Guilford also posited separate abilities, but he placed his estimate at 180 factors. Raymond Cattell and John Horn distinguished between two types of intelligence: fluid intelligence, which consists of biologically based mental abilities that are relatively free of cultural influences, and crystallized intelligence, which consists of mental skills acquired through experience in a particular cultural context. Psychometric models have successfully demonstrated individual differences in various mental tasks.
   2. Information-processing approaches
      Information-processing models focus on mental processes rather than on mental structures. Some of these models have suggested that differences in the speed of cognitive activities, as measured by reaction times in children and adults, reflect differences in intelligence. Processing times, however, may differ among individuals due to motivational, attentional, and cultural factors rather than to differences in intelligence.
      A new approach to intelligence examines individual differences in working memory. Successful performance on working memory tasks is related to scores on intelligence tests, and may be an even better predictor of intelligence than processing speed.
      Robert Sternberg's triarchic theory of intelligence emphasizes global and specific skills. His theory combines three major subtheories of intelligence to precisely define the large number of cognitive processes and abilities necessary for human intelligence: the individual's ability to adapt to a new environment (contextual subtheory), to process information effectively and efficiently (componential subtheory), and to deal with novelty and the automatization of cognitive processes (two-facet subtheory). Howard Gardner places greater emphasis on eight specific skills in his theory of multiple intelligences and stresses the role that culture plays in defining intelligence by specifying the skills that it values.
      
      
2. Measuring intelligence
   The scores on standardized tests of intelligence, such as the IQ test, are assumed to be normally distributed in the population. Because of the statistical nature of normal curves, the percentage of people attaining each possible score can be estimated.
   
   

   Atypical Development: Exceptional Intelligence Children who obtain an IQ score above 130 are often classified as gifted, and children who score below 70 are often classified as mentally retarded. Gifted children may have exceptional abilities in a number of domains. The most extensive study of gifted children, conducted by Lewis Terman over many decades, revealed that these individuals generally achieve considerable success throughout life. Moreover, giftedness may not always be the result of biological factors since gifted children often exercise their talents to a great extent. The difference between gifted and other children appears to be one of degree in more effective planning, dealing with novelty and automatizing routines, and speedier processing of information. Mental retardation consists of limitations in intellectual and adaptive functioning before age 18. Some cases of mental retardation can be linked to genetic and biological factors, however, most instances have no obvious organic roots and may be due to an impoverished, unstimulating environment. Children with mental retardation often develop just as other children do, although somewhat slower and to a lesser degree in cognitive abilities. The label mental retardation has negative connotations and has led to new efforts in the classroom to promote educational achievements, including mainstreaming.

   
   
   1. Standardized tests of intelligence
      Psychometricians construct and interpret tests of intelligence. Some tests are administered to individuals, while others are given to groups. Infant tests of intelligence are administered individually. The Bayley Scales of Infant Development, specifically designed to predict later childhood competence, measures mental and motor abilities. The Fagan Test of Infant Intelligence measures infants' recognition memory as determined by their visual fixations to novel stimuli. The Fagan Test shows some predictive ability for intelligence at three years of age.
      Individually administered tests for older children include the Stanford-Binet Intelligence Scale, the Wechsler Intelligence Scale for Children-Revised (WISC-R), and the Kaufman Assessment Battery for Children (K-ABC). Alfred Binet first introduced the concept of mental age, an expression of a child's mental abilities. Lewis Terman modified and standardized the Binet scales and introduced the intelligence quotient (IQ). In the newest version of the Stanford-Binet test, a deviation IQ is provided for each of four different test areas. The Wechsler Intelligence Scale for Children provides information about IQ based on verbal performance and on visual-spatial skill. The Kaufman Assessment Battery differs from the other two tests in that it focuses on how children process information rather than on the level of abilities that children display.
   2. Stability and prediction
      Many psychologists believe that intelligence tests administered early in life can be used to predict future performance. Two longitudinal studies, the Berkeley Growth Study and the Fels Longitudinal Study, found that although IQ scores are fairly stable from the preschool years to early adulthood, large fluctuations in IQ scores also occur. Shifts in IQ scores result from environmental influences such as the presence or absence of family stress and parents' child-rearing styles. Correlations between some infant measures of intelligence and later childhood measures have been low. Higher correlations are seen when measures of visual attention in infancy are compared to cognitive and language proficiency at three to five years.
      IQ tests are generally good for predicting which children will succeed in school. Although IQ tests are also good predictors of job status, it may be that IQ influences job status indirectly through educational attainment. More disagreement is found for predictive value of IQ for other measures, such as general life satisfaction.
      
      

      Research Applied to Education: Interpreting IQ Test Scores Many psychologists advocate that educators and parents use caution when interpreting IQ test scores because low scores may result from a number of factors, including poor motivation, anxiety, unfamiliarity with the language, or different cultural experiences. In addition, labeling a child as an "underachiever" or a "slow learner" on the basis of IQ score may affect teacher expectations. IQ test scores do not have direct application for educational practices or instructional techniques. Other information in addition to IQ score must be used to evaluate children's intellectual abilities.

      
      
      
3. Factors related to intelligence
   As we have seen in earlier chapters, chromosomal and prenatal events can influence intelligence. However, appropriate environmental arrangements can sometimes dramatically benefit intellectual development in a positive way. Evidence exists that performance on culture-fair intelligence tests has improved by as much as 15 points in about every thirty years of evaluation as a consequence of the improved environments in which children are reared, a phenomenon called the "Flynn effect."
   1. Group differences in IQ scores
      Children from different socioeconomic and ethnic backgrounds do not perform equally well on IQ tests. Arthur Jensen argued that lower IQ scores among African Americans compared to Caucasians are due largely to genetic, or heritability, factors. Hernstein and Murray made similar claims more recently. Their conclusions were criticized on several grounds; the strongest criticism stressed the difficulty of explaining between-group differences in intelligence with estimates of within-group heritability. Cross-fostering studies have provided considerable support for the strong role of environmental influences on IQ scores of African American children, but they have also provided support for a role of heredity in intelligence. Some psychologists argue that group differences in IQ are a result of test bias. Traditional psychometric tests are seen as not being culturally fair for children of some social and cultural backgrounds. Tests that have been described as culturally fair have yielded mixed results; some have found group differences similar to those seen with more traditional tests, while others have yielded smaller group differences than those typically observed. Another explanation of observed group differences in IQ scores centers on the differences between minority and majority children in terms of experience with and attitude toward test taking. Stereotype threat, or how an individual thinks about his or her abilities in relation to negative stereotypes about gender or race, can also affect performance.
   2. The role of early experiences
      The Home Observation for Measurement of the Environment (HOME) inventory was designed to examine the quality of caregiver-child interactions in the home and its relationship to later IQ scores and other competencies. Studies have found significant relationships between certain features of the home environment and later IQ scores, language proficiency, and school achievement. Parental emotional and verbal responsivity to the child and the degree of parental involvement with the child were among the important factors identified.
      
      

      Examining Research Methods: Using Correlations to Test Models of Causality Correlational studies do not provide strong evidence about causality. For example, parents' expectations may influence or be influenced by their children's performance on tests. A sophisticated statistical technique called structural equation modeling attempts to provide better information about the direction of influence involved in correlational relationships. An illustration of structural equation modeling is provided in the text. Measurements of the home environment, as well as the encouragement parents provide and the involvement they display with their children for learning and educational activities, are evaluated with respect to math motivation several years later. Path diagrams provide a pictorial summary of the directionality in which influences are hypothesized to have their effects. How well the path "explains" the findings are represented by path coefficients, measurements similar to correlations and which highlight how closely a difference at the end of the assessment is associated with earlier assessments of performance. Because structural equation modeling is still based on correlational data, inferences about causality remain uncertain, although such procedures come closer than simple correlational data in informing researchers about causal relationships.

      
      One of the earliest nationwide programs in the United States designed to promote intellectual development in very young children was Head Start. It placed children from lower socioeconomic classes into programs that provided them with the cognitive stimulation presumed to be available to more advantaged middle-class children. Although initial evaluations were not very favorable, subsequent assessments have shown that IQ is benefited somewhat from this experience at least for the short term. The Carolina Abecedarian Project aimed to prevent lower intellectual functioning of infants determined to be at risk, by providing them with medical and nutritional assistance, as well as a structured program of day care. As with the Head Start program, critics argued that the increases in intellectual functioning initially observed to result from this program were transitory. More lasting effects of these early intervention programs may be evident when measures other than IQ, such as social competence and general success in school, are examined. To be successful, early intervention efforts need to begin early in development, should provide a broad array of health and social services, and are more effective when support continues beyond the preschool years.
   3. The child's sociocultural environment
      To better understand the role of culture in the development of intellectual abilities, psychologists have examined various cultures in terms of (1) the activities and behaviors that are essential for adaptation and survival within the culture, (2) parental attitudes toward the role of the child in the culture, and (3) the emphasis the culture places on the formal schooling of its children.