Intelligence Theory pp


Gateway THEME Measuring intelligence is worthwhile, but tests provide limited definitions of intelligent behavior.

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Unlike other species, humans owe their success more to thinking abilities and intelligence than to physical strength or speed. That’s why our species is called Homo sapiens (from the Latin for man and wise). Our intelligence makes us highly adaptable creatures. We live in deserts, jungles, mountains, frenzied cities, placid retreats, and space stations.

Consider Stephen Hawking. He can’t walk or talk. When he was 13, Lou Gehrig’s disease began to slowly destroy nerve cells in his spinal cord, short-circuiting messages between his brain and muscles. Today, he is confined to a wheelchair and “speaks” by manually controlling a speech syn- thesizer. Yet, despite his severe disabilities, his brain is unaffected by the disease and remains fiercely active. He can still think. Stephen is a theoretical physicist and one of the best-known sci- entific minds of modern times. With courage and determination, he has used his intellect to advance our understanding of the universe.

What do we mean when we say that a person like Stephen Hawking is “smart” or “intelligent”? Can intelligence be measured? Can intelligence tests predict life success? What are the conse- quences of having extremely high or low intelligence? These questions and others concerning intelligence have fascinated psychologists for more than 100 years. Let’s see what has been learned and what issues are still debated.

Gateway QUESTIONS 9.1 How do psychologists define intelligence? 9.2 What are typical IQ tests like? 9.3 How do IQ scores relate to sex, age, and

occupation? 9.4 What does IQ tell us about genius?

9.5 What causes intellectual disability? 9.6 How do heredity and environment affect

intelligence? 9.7 Are there alternate views of intelligence? 9.8 Is there a downside to intelligence testing?



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Chapter 9304

Defining Intelligence— Intelligence Is … You Know, It’s …

Gateway Question 9.1: How do psychologists define intelligence? Like many important concepts in psychology, intelligence cannot be observed directly. Nevertheless, we feel certain it exists. Let’s compare two children:

When she was 14 months old, Anne wrote her own name. She taught her- self to read at age 2. At age 5, she astounded her kindergarten teacher by bringing an iPad to class—on which she was reading an encyclopedia. At 10, she breezed through an entire high school algebra course in 12 hours.

Billy, who is 10 years old, can write his name and can count, but he has trouble with simple addition and subtraction problems and finds multipli- cation impossible. He has been held back in school twice and is still incapa- ble of doing the work his 8-year-old classmates find easy.

Anne is considered a genius; Billy, a slow learner. There seems little doubt that they differ in intelligence.

Wait! Anne’s ability is obvious, but how do we know that Billy isn’t just lazy? That’s the same question that Alfred Binet faced in 1904 (Benjafield, 2010; Jarvin & Sternberg, 2003). The French minister of education wanted to find a way to distinguish slower students from the more capable (or the capable but lazy). In a flash of bril- liance, Binet and an associate created a test made up of “intellec- tual” questions and problems. Next, they learned which questions an average child could answer at each age. By giving children the test, they could tell whether a child was performing up to his or her potential (Kaplan & Saccuzzo, 2009; Kaufman, 2000).

Binet’s approach gave rise to modern intelligence tests. At the same time, it launched an ongoing debate. Part of the debate is related to the basic difficulty of defining intelligence (Sternberg, Grigorenko, & Kidd, 2005).

Defining Intelligence Isn’t there an accepted definition of intelligence? Traditionally, yes. Intelligence is the global capacity to act purposefully, to think rationally, and to deal effectively with the environment (Wechsler, 1939). The core of intelligence is usually thought to consist of a small set of general mental abilities (called the g-factor) in the areas of reasoning, problem solving, knowledge, memory, and successful adaptation to one’s surroundings (Barber, 2010; Sternberg, 2004).

Intelligence has traditionally been considered a cognitive, not an emotional, capacity. Is there such a thing as emotional intelligence? To find out, see Chapter 10, pages 363–364.


Beyond this, however, there is much disagreement. In fact, many psychologists simply accept an operational definition of intelligence by spelling out the procedures they use to measure it (Neukrug & Fawcett, 2010). Thus, by selecting items for an intel- ligence test, a psychologist is saying in a very direct way, “This is

what I mean by intelligence.” A test that measures memory, reason- ing, and verbal fluency offers a very different definition of intelli- gence than one that measures strength of grip, shoe size, length of the nose, or the person’s best Guitar Hero score (Goldstein, 2011).

Aptitudes As a child, Hedda displayed an aptitude for art. Today, Hedda is a successful graphic artist. How does an aptitude like Hedda’s differ from general intelligence? An aptitude is a capacity for learning certain abilities. Persons with mechanical, artistic, or musical apti- tudes are likely to do well in careers involving mechanics, art, or music, respectively (• Figure 9.1).

Are there tests for aptitudes? How are they different from intelli- gence tests? Aptitude tests measure a narrower range of abilities than do intelligence tests (Kaplan & Saccuzzo, 2009). For example, special aptitude tests predict whether you will succeed in a single


Multiple aptitude tests

Special aptitude tests

Intelligence tests

Modern intelligence tests are widely used to measure cognitive abilities. When properly administered, such tests provide an operational definition of intelligence.

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• Figure 9.1 Special aptitude tests measure a person’s potential for achieve- ment in a limited area of ability, such as manual dexterity. Multiple aptitude tests measure potentials in broader areas, such as college work, law, or medicine. Intelli- gence tests measure a very wide array of aptitudes and mental abilities.

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Intelligence 305

Intelligence An overall capacity to think rationally, act purposefully, and deal effectively with the environment.

g-factor A general ability factor proposed to underly intelligence; the core of general intellectual ability that involves reasoning, problem-solving ability, knowledge, and memory.

Operational definition The operations (actions or procedures) used to measure a concept.

Aptitude A capacity for learning certain abilities. Special aptitude test Test to predict a person’s likelihood of succeeding in

a particular area of work or skill. Multiple aptitude test Test that measures two or more aptitudes. General intelligence test A test that measures a wide variety of mental

abilities. Psychometric test Any scientific measurement of a person’s mental

functions. Reliability The ability of a test to yield the same score, or nearly the same

score, each time it is given to the same person. Validity The ability of a test to measure what it purports to measure. Objective test A test that gives the same score when different people

correct it. Test standardization Establishing standards for administering a test and

interpreting scores. Norm An average score for a designated group of people.

area, such as clerical work or computer programming (• Figure 9.2). Multiple aptitude tests measure two or more types of ability. These tests tend to be more like intelligence tests. The well-known SAT Reasoning Test (SAT), which measures aptitudes for language, math, and reasoning, is a multiple aptitude test. So are the tests required to enter graduate schools of law, medicine, business, and dentistry. The broadest aptitude measures are general intelligence tests, which assess a wide variety of mental abilities (Cohen & Swerdlik, 2005).

Psychologists use a variety of aptitude tests to select people for employment and to advise people about choosing careers. For more information, see Chapter 18, pages 608–611.


Reliability and Validity Whether it is an intelligence test or aptitude test or, for that matter, any other kind of psychometric test—any measurement of a per- son’s mental functions—there will always be two questions you should ask about the test: “Is it reliable?” and “Is it valid? ”

To what does reliability refer? If you weigh yourself several times in a row, a reliable bathroom scale gives the same weight each time. Likewise, a reliable psychometric test must give approximately the same score each time a person takes it (Kaplan & Saccuzzo, 2009). In other words, the scores should be consistent and highly corre- lated. It is easy to see why unreliable tests have little value. Imagine a medical test for pregnancy or breast cancer, for instance, which gives positive and negative responses for the same woman on the same day.

To check the reliability of a test, we could give it to a large group of people. Then, each person could be tested again a week later to establish test-retest reliability. We also might want to know whether scores on one half of the test items match scores on the other half (split-half reliability). If two versions of a test are avail-

able, we could compare scores on one version to scores on the other (equivalent-forms reliability).

Just because a psychometric test is reliable, however, does not mean that it should be trusted; test validity is also important. To see why this is the case, try creating an IQ test with ten questions only you could possibly answer. Your test would be very reliable. Each time you give the test, everyone scores zero, except you, who scores 100  percent (so you thereby proclaim yourself the only human with any intelligence). Even though we all have days when it seems we are the only smart person left on the planet, it should be obvious this is a silly example. A test must also have validity; it should measure what it claims to measure (Neukrug & Fawcett, 2010). By no stretch of the imagination could a test of intelligence be valid if the person who wrote it is the only one who can pass it.

How is validity established? Validity is usually demonstrated by comparing test scores to actual performance. This is called criterion validity. For example, scores on a test of legal aptitude might be com- pared with grades in law school. If high test scores correlate with high grades, or some other standard (criterion) of success, the test might be valid. Unfortunately, many “free” tests you encounter, such as those found in magazines and on the Internet, have little or no validity.

Objective Testing Let’s return to your “I’m the Smartest Person in the World IQ Test” for a final point. Is your test objective? Actually, it might be. If your IQ test gives the same score when corrected by different people, it is an objective test. However, objectivity is not enough to guaran- tee a fair test. Useful tests must also be standardized (Neukrug & Fawcett, 2010).

Test standardization refers to two things. First, it means that standard procedures are used in giving the test. The instructions, answer forms, amount of time to work, and so forth, are the same for everyone. Second, it means finding the norm, or average score,

1. If the driver turns in the direction shown, which direction will wheel Y turn? A B

2. Which wheel will turn the slowest? Driver X Y






• Figure 9.2 Sample questions like those found on tests of mechanical apti- tude. (The answers are A and the Driver.)

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Chapter 9306

made by a large group of people like those for whom the test was designed. Without standardization, we couldn’t fairly compare the scores of people taking the test at different times. And without norms, there would be no way to tell whether a score is high, low, or average.

Later in this chapter, we will address the question of whether intelligence tests are valid. For now, let’s take a practical approach and learn about some popular standardized IQ tests.

Testing Intelligence—The IQ and You

Gateway Question 9.2: What are typical IQ tests like? American psychologists quickly saw the value of Alfred Binet’s test. In 1916, Lewis Terman and others at Stanford University revised it for use in North America. After more revisions, the Stanford-Binet Intelligence Scales, Fifth Edition (SB5) continue to be widely used. The original Stanford-Binet assumed that a child’s intellectual abilities improve with each passing year. Today, the Stanford-Binet (or SB5) is still primarily made up of age-ranked questions. Naturally, these questions get a little harder at each age level. The SB5 is appropriate for people from age 2 to 85� years and scores on the test are very reliable (Raid & Tippin, 2009; Roid, 2003).

Five Aspects of Intelligence The SB5 measures five cognitive factors (types of mental abilities) that make up general intelligence. These are fluid reasoning, knowl- edge, quantitative reasoning, visual-spatial processing, and working memory. Each factor is measured with verbal questions (those involving words and numbers), and nonverbal questions (items that use pictures and objects). Let’s see what each factor looks like.

Fluid Reasoning Questions like the following are used to test Fluid Reasoning:

How are an apple, a plum, and a banana different from a beet? An apprentice is to a master as a novice is to an ____________. “I knew my bag was going to be in the last place I looked, so I

looked there first.” What is silly or impossible about that?

Other items ask people to fill in the missing shape in a group of shapes, and to tell a story that explains what’s going on in a series of pictures.

Knowledge The Knowledge factor assesses the person’s knowledge about a wide range of topics.

Why is yeast added to bread dough? What does cryptic mean? What is silly or impossible about this picture? (For example, a

bicycle has square wheels.)

Quantitative Reasoning Test items for Quantitative Reasoning measure a person’s ability to solve problems involving numbers. Here are some samples:

If I have six marbles and you give me another one, how many marbles will I have?

Given the numbers 3, 6, 9, 12, what number would come next? If a shirt is being sold for 50 percent of the normal price, and

the price tag is $60, what is the cost of the shirt?

Visual-Spatial Processing People who have visual-spatial skills are good at putting picture puzzles together and copying geometric shapes (such as triangles, rectangles, and circles). Visual-Spatial Processing questions ask test takers to reproduce patterns of blocks and choose pictures that show how a piece of paper would look if it were folded or cut. Verbal questions can also require visual-spatial abilities:

Suppose that you are going east, then turn right, then turn right again, then turn left. In what direction are you facing now?

Working Memory The Working Memory part of the SB5 measures the ability to use short-term memory. Some typical memory tasks include the following:

Correctly remember the order of colored beads on a stick. After hearing several sentences, name the last word from each

sentence. Repeat a series of digits (forward or backward) after hearing

them once. After seeing several objects, point to them in the same order as

they were presented.

If you were to take the SB5, it would yield a score for your general intelligence, verbal intelligence, nonverbal intelligence, and each of the five cognitive factors (Bain & Allin, 2005). For another per- spective on the kinds of tasks used in the SB5, see “Intelligence— How Would a Fool Do It?”

The Wechsler Tests Is the Stanford-Binet the only intelligence test? Many other IQ tests have been developed. Psychologist David Wechsler (1939) designed one widely used alternative. Whereas the original Stanford-Binet was better suited for children and adolescents, the first Wechsler test was specifically designed to test adult intelligence. The current version is the Wechsler Adult Intelli- gence Scale—Fourth Edition (WAIS-IV). With newer versions of the Stanford-Binet and a children’s version of the Wechsler scales (currently the Wechsler Intelligence Scale for Children— Fourth Edition or WISC-IV; see Baron, 2005), both alternatives are now widely used across all ages.

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Intelligence 307

Performance intelligence Intelligence measured by solving puzzles, assembling objects, completing pictures, and other nonverbal tasks.

Verbal intelligence Intelligence measured by answering questions involving vocabulary, general information, arithmetic, and other language- or symbol-oriented tasks.

Individual intelligence test A test of intelligence designed to be given to a single individual by a trained specialist.

Group intelligence test Any intelligence test that can be administered to a group of people with minimal supervision.

Like the Stanford-Binet, the Wechsler tests yield a single overall intelligence score. In addition, these tests also separate scores for performance (nonverbal) intelligence and verbal (language- or symbol-oriented) intelligence. The abilities measured by the Wechsler tests and some sample test items are listed in ■ Table 9.1.

Group Tests The SB5 and the Wechsler tests are individual intelligence tests, which are given to a single person by a trained specialist. In con- trast, group intelligence tests can be given to a large group of people with minimal supervision. Group tests usually require people to read, to follow instructions, and to solve problems of logic, reasoning, mathematics, or spatial skills. The first group intelligence test was the Army Alpha, developed for World War I military inductees. As you can see in ■ Table 9.2, intelligence test- ing has come a long way since then.

Scholastic Aptitude Tests If you’re wondering if you have ever taken an intelligence test, the answer is probably yes. As mentioned earlier, the SAT Reasoning Test is a multiple aptitude test. So are the American College Test (ACT) and the College Qualification Test (CQT). Each of these group tests is designed to predict your chances for success in col-

Adapted from Wechsler, D. (2008). Wechsler Adult Intelligence Scale, Fourth Edition (WAIS-IV). San Antonio, TX: Pearson.

Sample Items Similar to Those Used on the WAIS-IV

Verbal Comprehension Sample Items or Descriptions

Similarities In what way are a wolf and a coyote alike?

In what way are a screwdriver and a chisel alike?

Vocabulary The test consists of asking, “What is a ____________?” or “What does ____________ mean?” The words range from more to less familiar and difficult.

Information How many wings does a butterfly have?

Who wrote Romeo and Juliet?

Perceptual Reasoning

Block Design Copy designs with blocks (as shown at right).

Matrix Reasoning Select the item that completes the matrix.

Visual Puzzles Choose the pieces which go together to form a figure.

Working Memory

Digit Span Repeat from memory a series of digits, such as 8 5 7 0 1 3 6 2, after hearing it once.

Arithmetic Four girls divided 28 jellybeans equally among themselves. How many jellybeans did each girl receive?

If 3 peaches take 2 minutes to find and pick, how long will it take to find and pick a dozen peaches?

Processing Speed

Symbol Search Match symbols appearing in separate groups.




Symbol Search

Coding Fill in the symbols: 3 21244 1 31 2 3 4


■ TABLE 9.1

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Chapter 9308

Intelligence—How Would a Fool Do It?Human Diversity

You have been asked to sort some objects into categories. Wouldn’t it be smart to put the clothes, containers, implements, and foods in separate piles? Not necessarily. When members of the Kpelle culture in Libe- ria were asked to sort objects, they grouped them together by function. For example, a potato (food) would be placed together with a knife (implement). When the Kpelle were asked why they grouped the objects this way, they often said that was how a wise man would do it. The researchers finally asked the Kpelle, “How would a fool do it?” Only then did the Kpelle sort the objects into the nice, neat categories that we Westerners prefer.

This anecdote, related by cultural psy- chologist Patricia Greenfield (1997), raises serious questions about general definitions of intelligence. For example, among the Cree of northern Canada, “smart” people are the ones who have the skills needed to find food on the frozen tundra (Darou, 1992). For the Puluwat people in the South Pacific, smart means having ocean-going naviga- tion skills necessary to get from island to is- land (Sternberg, 2004). And so it goes, as each culture teaches its children the kinds of “intelligence” valued in that culture— how the wise man would do it, not the fool (Barber, 2010; Correa-Chávez, Rogoff, & Arauz, 2005).

How important do you think the mental abilities assessed in modern intelligence tests are to this Bushman hunter in Africa’s Kalahari Desert?

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Items from the Army Alpha Subtest on “Common Sense”

The Army Alpha was given to World War I army recruits in the United States as a way to identify potential officers. In these sample questions, note the curious mixture of folk wisdom, scientific information, and moralism (Kessen & Cahan, 1986). Other parts of the test were more like modern intelligence tests.

1. If plants are dying for lack of rain, you should

h water them

h ask a florist’s advice

h put fertilizer around them

2. If the grocer should give you too much money in making change, what is the right thing to do?

h buy some candy for him with it

h give it to the first poor man you meet

h tell him of his mistake

3. If you saw a train approaching a broken track you should

h telephone for an ambulance

h signal the engineer to stop the train

h look for a piece of rail to fit in

4. Some men lose their breath on high mountains because

h the wind blows their breath away

h the air is too rare

h it is always cold there

5. We see no stars at noon because

h they have moved to the other side of the earth

h they are much fainter than the sun

h they are hidden behind the sky

■ TABLE 9.2

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Intelligence 309

Mental age The average mental ability displayed by people of a given age. Chronological age A person’s age in years. Intelligence quotient (IQ) An index of intelligence defined as mental age

divided by chronological age and multiplied by 100. Deviation IQ An IQ obtained statistically from a person’s relative standing

in his or her age group; that is, how far above or below average the person’s score was relative to other scores.

lege. Because the tests measure general knowledge and a variety of mental aptitudes, each can also be used to estimate intelligence.

Intelligence Quotients What is an “IQ”? Imagine that a child named Yuan can answer intelligence test questions that an average 7-year-old can answer. We could say that 7 is her mental age (average intellectual perfor- mance). How smart is Yuan? Actually, we can’t say yet, because we don’t know how old Yuan is. If she is 10, she’s not very smart. If she’s 5, she is very bright. Thus, although mental age is a good measure of actual ability, it says nothing about whether overall intelligence is high or low, compared with other people of the same age.

Thus, to estimate a child’s intelligence, we also need to know her chronological age (age in years). Then, we can relate mental age to chronological age. This yields an IQ, or intelligence quotient. A quotient results from dividing one number into another. When the Stanford-Binet was first used, IQ was defined as mental age (MA) divided by chronological age (CA) and multiplied by 100. (Multi- plying by 100 changes the IQ into a whole number rather than a decimal.)


� 100 � IQ

An advantage of the original IQ was that intelligence could be compared among children with different chronological and mental ages. For instance, 10-year-old Justin has a mental age of 12. Thus, his IQ is 120:

1MA2 12 1CA2 10

� 100 � 120 (IQ)

Justin’s friend Suke also has a mental age of 12. However, Suke’s chronological age is 12, so his IQ is 100:

1MA2 12 1CA2 12

� 100 � 100 (IQ)

The IQ shows that 10-year-old Justin is brighter than his 12-year- old friend Suke, even though their intellectual skills are about the same. Notice that a person’s IQ will be 100 when mental age equals chronological age. Therefore, an IQ score of 100 is defined as aver- age intelligence.

Then does a person with an IQ score below 100 have below average intelligence? Not unless the IQ is well below 100. Average intelli- gence is usually defined as any score from 90 to 109. The impor- tant point is that IQ scores will be over  100 when mental age is higher than age in years. IQ scores below 100 occur when a per- son’s age in years exceeds his or her mental age. An example of this situation would be a 15-year-old with an MA of 12:

12 15

� 100 � 80 (IQ)

Deviation IQs Although the preceding examples may give you insight into IQ scores, it’s no longer necessary to directly calculate IQs. Instead, modern tests use deviation IQs. Tables supplied with the test are used to convert a person’s relative standing in the group to an IQ score. That is, they tell how far above or below average the person’s score falls. For example, if you score at the 50th percentile, half the people your age who take the test score higher than you and half score lower. In this case, your IQ score is 100. If you score at the 84th percentile, your IQ score is 115. If you score at the 97th per- centile, your IQ score is 130. (For more information, see the Statis- tics appendix near the end of this book.)

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Chapter 9310

OK, so how does Stephen Hawking score? When Hawking was once asked about his IQ, he claimed he didn’t know and joked, “People who boast about their IQ are losers.”

The Stability of IQ How old do children have to be before their IQ scores become stable? IQ scores are not very dependable until about age 6 (Schuerger & Witt, 1989). IQ scores measured at age  3 correlate poorly with those measured at age 27. In …