Chapters 9-11: Intelligence and Psychological Testing PDF

CHAPTER 9 THEMES IN THIS CHAPTER Sociohistorical Context Cultural Heritage Heredity & Environment...

CHAPTER 9 THEMES IN THIS CHAPTER Sociohistorical Context Cultural Heritage Heredity & Environment Steve Tulley/Alamy Stock Photo Intelligence and Psychological Testing Key Concepts in Psychological Testing 330 The Evolution of Intelligence Testing and Our Understanding of the Construct of Intelligence 332 Basic Issues in Intelligence Testing 340 Extremes of Intelligence 343 Heredity and Environment as Determinants of Intelligence 347 Putting It in Perspective: Themes 3, 5, and 6 354 PERSONAL APPLICATION Understanding Creativity 356 CRITICAL THINKING APPLICATION The Intelligence Debate, Appeals to Ignorance, and Reification 359 Concept Chart 361 328 02940_ch09_ptg01.indd 328 08/01/21 9:32 PM  A s we suggested in Chapter 3, people seem to be continuously fascinated with the brain. The research and theory we discussed in that chapter revealed the many important functions that the brain serves and the abilities it affords us. Among these, of course—and this may be part of the reason for our fascination—is the notion of intelligence. In this chapter we will discuss the scientific theories of intelligence and intelligence testing. Of course, you do not have to be a scientist to have a theory about the Photo by Alfred Eisenstaedt/Pix Inc./The nature of intelligence and whether or not it is immu- LIFE Picture Collection/Getty Images table. According to Carol Dweck (2000, 2002), many of the rest of us have our own beliefs about the nature of intelligence—lay theories of intelligence that affect our own behaviour and how we view others. According to Dweck, many of us adopt either an entity or incremental theory of intelligence. People who adopt an entity theory of intelligence believe that intel- Albert Einstein, one of history’s great intellectuals, failed ligence is fixed at birth and is not affected by experi- Thomas Edison’s trivia test of intelligence. ences or attempts to change it. On the other hand, those who adopt an incremental theory of intelligence No matter how dismal his performance on believe that their intelligence can be changed by effort Edison’s test, when many of us think of highly intel- and seeking out formative experiences. In this chapter ligent people we often apply the label “genius” to we will detail what scientists know about the nature of someone like Albert Einstein. Einstein made critical intelligence and the extent to which it is inherited at contributions to our understanding of the nature birth, affected by our experiences, or both. of the universe, some of which we are only now, Being smart or highly intelligent is often seen as a decades later, able to evaluate and confirm (Holz, guarantee of success. If this is true, and we will evaluate 2011). Surely, any list of geniuses must also contain the validity of this idea later in the chapter, then it Marie Curie, who won two Nobel prizes in two dif- makes sense that we should try to determine our abso- ferent sciences. She is the only person to have ever lute or relative level of intelligence. As we are growing achieved that (Nobel Lectures, 1967). Closer to up, it seems as if we are always trying to answer ques- home, some of us might point to Gerhard Herzberg, tions such as “Am I smart?” or “Who is the smartest a Canadian who won Canada’s first Nobel Prize in kid in the class?” Of course, these questions raise addi- Chemistry in 1971. Canadians have won the Nobel tional questions such as “What is intelligence?” and Prize in Chemistry six times. Herzberg’s main con- “How would you know if you were intelligent?” The tributions were to the field of atomic and molecular last question is a difficult one to answer, and it often spectroscopy (Stoicheff, 2002). leads us to look for markers/tests of intelligence. But how can we assess someone’s level of intelligence? Thomas Edison, one of the greatest and most cre- ative of American inventors, thought trivia was a way to assess intelligence and ability level and so he devel- oped his own trivia intelligence test to give to pro- The Canadian Press Images/Ottawa Citizen spective employees. But how do we know it is a valid test of intelligence? There was little scientific interest in Edison’s test, but we do have one result that might help you decide about its status as a reliable and valid IQ test. On a visit to the United States in 1921, Albert Einstein took the test. His results were announced Photo by Hulton Archives/Getty Images to the world by the New York Times in its headline: “Einstein Sees Boston: Fails on Edison Test” (New York Gerhard Herzberg (left) won the Nobel Times, 1921). Einstein did not know, for example, the Prize in Chemistry in 1971. He worked at the University of Saskatchewan and the speed of sound. He did not think it was important to National Research Council. Marie Curie remember such things since they are “readily avail- (right) won the Nobel Prize twice—in able” in textbooks. Physics in 1903 and for Chemistry in 1911. Intelligence and Psychological Testing 329 02940_ch09_ptg01.indd 329 08/01/21 9:32 PM  Variation in intelligence, especially assumed low We’ll begin by introducing some basic concepts intelligence, has had important personal conse- in psychological testing. Then we’ll explore the his- quences for many Canadians. Consider, for example, tory of intelligence tests because they provided the the story of Leilani Muir, who was sterilized in 1959 model for subsequent psychological tests. Next we’ll at the age of 14 in Alberta (Pringle, 1997; Wahlsten, address practical questions about how intelligence Edmonton Journal-Shaughn Butts 1997). She had tested low on one IQ test and was con- tests work. And we’ll explore some recent develop- sidered a “mental defective.” Before the operation, ments in the study of intelligence. Along the way, she was deceived and was told she was having sur- we will also discuss how racism has been implicated gery on her appendix. She was a resident of Alberta’s in the scientific debate about the nature of group Provincial Training School for Mental Defectives and differences in IQ and the primacy of genetics in was one of many who suffered a similar fate. She explaining those group differences (Gould, 1996; Leilani Muir was sterilized learned about her sterilization after she consulted Jensen, 1969). In the Personal Application, we’ll dis- without her consent at physicians due to her inability to conceive. She later cuss efforts to measure and understand another type the age of 14 in 1959. She later successfully sued the successfully sued the Government of Alberta and was of mental ability: creativity. In the Critical Thinking Government of Alberta for awarded a settlement of $740,000 and legal costs. Application, we will critique some of the reasoning wrongful sterilization under She died at age 72 in 2016. She was a life-long advo- used in the vigorous debate about the roots of the Sexual Sterilization Act of Alberta. Leilani passed away cate on behalf of people who were treated as she was. intelligence. on March 12, 2016. Key Concepts in Psychological Testing A psychological test is a standardized measure of aspects of personality, including motives, interests, KEY LEARNING GOALS a sample of a person’s behaviour. Psychological values, and attitudes. If you had to describe yourself tests are measurement instruments. They’re used to in a few words, what words would you use? Are you Identify the main categories of psycho- measure the individual differences that exist among introverted? Independent? Ambitious? Enterprising? logical tests and dis- people in such things as intelligence, aptitudes, Conventional? Assertive? Domineering? Words such cuss what makes a test interests, and aspects of personality. as these refer to personality traits. These traits can be standardized. Intelligence tests measure general mental ability. assessed systematically with personality tests. Describe test norms, percentile scores. They’re intended to assess intellectual potential rather Many psychologists prefer to call these tests per- Discuss the nature of than previous learning or accumulated knowledge. sonality scales because, unlike tests of mental abili- reliability and how it is Aptitude tests are also designed to measure potential ties, the questions do not have right and wrong measured and identify more than knowledge, but they break mental ability answers. We’ll look at the various types of person- the three types of validity. into separate components. Thus, aptitude tests assess ality scales in Chapter 12. specific types of mental abilities. Your responses to a psychological test represent Like aptitude tests, achievement tests have a spe- a sample of your behaviour. The word sample should cific focus, but they’re supposed to measure previous alert you to one of the key limitations of psycho- learning instead of potential. Thus, achievement logical tests: A particular behaviour sample may not tests gauge a person’s mastery and knowledge of be representative of your characteristic behaviour. various participants (such as reading, English, or Everyone has bad days. A stomachache, a fight with history). Finally, personality tests measure various a friend, a problem with your car—all might affect your responses to a particular test on a particular day. Because of the limitations of the sampling process, test scores should always be interpreted cautiously. Standardization and Norms Both personality scales and tests of mental abilities are standardized measures of behaviour. Standardization Mike Flippo/Shutterstock.com refers to the uniform procedures used in the admin- istration and scoring of a test. All participants get the same instructions, the same questions, and the same time limits so that their scores can be compared meaningfully. The standardization of a test’s scoring system Most children become familiar with standardized psycholog- ical tests—intelligence, achievement, and aptitude tests—in includes the development of test norms. Test norms school settings. provide information about where a score on a 330 CHAPTER 9 02940_ch09_ptg01.indd 330 08/01/21 9:32 PM  psychological test ranks in relation to other scores 2005). One widely used approach is to check test– on that test. The sample of people that the norms retest reliability, which is estimated by comparing par- are based on is called a test’s standardization group. ticipants’ scores on two administrations of a test. Ideally, test norms are based on a large sample of Reliability estimates require the computation people who were carefully selected to be representa- of correlation coefficients, which we introduced in tive of the broader population. For example, sepa- Chapter 2 (see Figure 9.1 for a brief recapitulation). rate norms have been developed for Canadians and A correlation coefficient is a numerical index of the Americans on most intelligence tests. This might degree of relationship between two variables. In esti- seem odd—aren’t we very similar to those living to mating test–retest reliability, the two variables that the south of us? Even though Canadian and U.S. soci- must be correlated are the two sets of scores from eties are similar in many ways, there are also many the two administrations of the test. If people get important differences in culture, language, and edu- fairly similar scores on the two administrations of cational systems that might be important consider- our hypothetical assertiveness test, this consistency ations when evaluating an individual’s performance yields a substantial positive correlation. The magni- on a test. Thus, for many tests, the most appropriate tude of the correlation gives us a precise indication comparison group is other Canadians of similar age of the test’s consistency. The closer the correlation and status. Although intelligence tests have been comes to +1.00, the more reliable the test is. standardized pretty carefully, the representativeness of standardization groups for other types of tests Validity varies considerably from one test to another. Even if a test is quite reliable, we still need to be con- Why are test norms needed? Because in psycho- cerned about its validity. Validity refers to the ability logical testing, everything is relative. Psychological of a test to measure what it was designed to measure. tests tell you how you score relative to other people. If we develop a new test of assertiveness, we have to They tell you, for instance, that you are average in provide some evidence that it really measures asser- creativity or slightly above average in clerical ability. tiveness. Increasingly, the term validity is also used These interpretations are derived from the test norms to refer to the accuracy or usefulness of the infer- that help you understand what your test score means. ences or decisions based on a test (Moss, 1994). This Usually, test norms allow you to convert your “raw broader conception of validity highlights the fact score” on a test into a percentile. A percentile score that a specific test might be valid for one purpose, indicates the percentage of people who score at or such as placing students in school, and invalid for below the score one has obtained. another purpose, such as making employment deci- sions for a particular occupation. The most common Reliability and useful techniques for establishing validity are Any kind of measuring device, whether it’s a tire gauge, content, criterion-related, and construct validity. a stopwatch, or a psychological test, should be rea- Achievement tests and educational tests such sonably consistent. That is, repeated measurements as classroom exams should have adequate content should yield reasonably similar results. Psychologists validity. Content validity refers to the degree to call this quality reliability. Consistency in measure- which the content of a test is representative of the ment is essential to accuracy in measurement. domain it’s supposed to cover. Reliability refers to the measurement consistency Criterion-related validity is estimated by corre- of a test (or of other kinds of measurement tech- lating participants’ scores on a test with their scores niques). Like most other types of measuring devices, on an independent criterion (another measure) of psychological tests are not perfectly reliable. A test’s the trait assessed by the test. For example, let’s say you reliability can be estimated in several ways (Hempel, developed a test to measure aptitude for becoming an Figure 9.1 Acceptable Correlation and reliability. As Negative correlation Positive correlation reliability coefficients explained in Chapter 2, a positive correlation means that two variables co-vary in the same direction; a negative correlation means that two variables co-vary in opposite directions. The closer the correlation coefficient High Moderate Low Low Moderate High gets to either +1.00 or –1.00, the stronger the relationship. At a minimum, –1.00 –.90 –.80 –.70 –.60 –.50 –.40 –.30 –.20 –.10 0.10.20.30.40.50.60.70.80.90 1.00 reliability estimates for psychological Strength of relationship tests must be moderately high positive correlations. Most reliability coefficients Increasing Increasing fall between 0.70 and 0.95. Intelligence and Psychological Testing 331 02940_ch09_ptg01.indd 331 08/01/21 9:32 PM  training. The performance ratings would be the inde- CONCEPT CHECK 9.1 pendent criterion of pilot aptitude. If your test has reasonable validity, there ought to be a reasonably Recognizing Basic Concepts in Testing strong positive correlation between the test and the Check your understanding of basic concepts in psychological testing by answering the criterion measure. Such a correlation would help vali- questions below. Select your responses from the following concepts. The answers are date your test’s predictive ability. in Appendix A near the back of the book. Many psychological tests attempt to measure Test norms Construct validity abstract personal qualities, such as creativity, intel- ligence, extraversion, or independence. No obvious Test–retest reliability Criterion-related validity Content validity criterion measures exist for these abstract qualities, 1. At the request of the HiTechnoLand computer store chain, Professor Charlz develops which are called hypothetical constructs. In measuring a test to measure aptitude for selling computers. Two hundred applicants for sales abstract qualities, psychologists are concerned about jobs at HiTechnoLand stores are asked to take the test on two occasions, a few construct validity—the extent to which there is weeks apart. A correlation of +0.82 is found between applicants’ scores on the two administrations of the test. Thus, the test appears to possess reasonable _________. evidence that a test measures a particular hypo- thetical construct. 2. All 200 of these applicants are hired and put to work selling computers. After six The process of demonstrating construct validity months, Professor Charlz correlates the new workers’ aptitude test scores with can be complicated. It depends on starting with a the dollar value of the computers that each sold during the first six months on the job. This correlation turns out to be –0.21. This finding suggests that the test clear idea of the hypothetical construct to be mea- may lack _________. sured (Clark & Watson, 2003; Jackson, 1968), and it usually requires a series of studies that examine the 3. Back at the university, Professor Charlz is teaching a course in theories of per- correlations between the test and various measures sonality. He decides to use the same midterm exam that he gave last year, even though the exam includes questions about theorists that he did not cover related to the trait in question. A thorough demon- or assign reading on this year. There are reasons to doubt the _________ of stration of construct validity requires looking at the Professor Charlz’s midterm exam. relationship between a test and many other mea- sures (Han, 2000). Ultimately, it’s the overall pattern of correlations between the test being developed airplane pilot. You could check its validity by corre- and tests assessing related concepts that provides lating participants’ scores on your aptitude test with convincing (or unconvincing) evidence of a test’s subsequent ratings of their performance in their pilot construct validity. The Evolution of Intelligence Testing and Our Understanding of the Construct of Intelligence Origins of Modern Intelligence Testing Nonetheless, his work was an important starting KEY LEARNING GOALS The use of elaborate tests for selection purposes point. In pursuing this line of investigation, Galton Summarize the con- dates back to the Chinese imperial examinations coined the phrase nature versus nurture to refer to tributions of Galton, that began over 1400 years ago. But the first modern the heredity–environment issue (Fancher, 2009). Binet, Terman, and psychological tests were invented only a little over Along the way, he also invented the concepts of cor- Wechsler to the evolu- tion of intelligence a century ago and began with the work of a British relation and percentile test scores (Roberts et al., 2005). testing. scholar, Sir Francis Galton, in the later part of the Although Galton’s mental tests measuring simple Describe what 19th century (Galton, 1909). Galton studied family sensory processes to assess intelligence or cognitive Spearman and trees and found that success and eminence appeared ability were a failure, his work created an interest in Thurstone said about the structure of intel- consistently in some families over generations. For the measurement of mental ability, setting the stage ligence and its current the most part, these families were much like Galton’s: for a subsequent breakthrough by Alfred Binet, a status. well-bred, upper-class families with access to superior prominent French psychologist. Describe the ways in schooling and social connections that pave the way The key breakthrough came in 1904, when a com- which the construct of intelligence has been to success. Yet Galton discounted the advantages mission on education in France asked Alfred Binet to broadened in recent of such an upbringing (Fancher, 2005). In his book devise a test to identify mentally subnormal children. formulations. Hereditary Genius (1869), Galton concluded that The commission wanted to single out youngsters in success runs in families because great intelligence need of special training. It also wanted to avoid com- is passed from generation to generation through plete reliance on teachers’ evaluations, which might genetic inheritance. often be subjective and biased. In response to this 332 CHAPTER 9 02940_ch09_ptg01.indd 332 08/01/21 9:32 PM  need, Binet and a colleague, Theodore Simon, created world’s foremost intelligence test and the standard a test that ultimately revolutionized the measurement of comparison for virtually all intelligence tests that of intellectual ability (Esping & Plucker, 2015). Their followed. Today, it remains one of the world’s most Photo12/Universal Images Group via Getty Images scale, first published in 1905, was a success because widely used psychological tests. it was inexpensive, easy to administer, objective, Further advances in intelligence testing came from and capable of predicting children’s performance in the work of David Wechsler (1939), who published the school fairly well (Siegler, 1992). Hence, its use spread first high-quality IQ test designed specifically for adults across Europe, and it became particularly popular in in 1939. His test, the Wechsler Adult Intelligence Scale America (Carson, 2014; Mulberger, 2014). (WAIS), introduced two major innovations (Benisz et The Binet-Simon scale expressed a child’s score in al., 2015). First, Wechsler made his test less dependent terms of “mental level” or “mental age.” A child’s on participants’ verbal ability than the Stanford-Binet. mental age indicated that they displayed the mental He included many items that required nonverbal rea- ability typical of a child of that chronological (actual) soning. To highlight the distinction between verbal ALFRED BINET age. Thus, a child with a mental age of six performed and nonverbal ability, he formalized the computation “The intelligence of anyone is susceptible of like the average six-year-old on the test. Binet realized of separate scores for verbal IQ, performance (non- development. With prac- that his scale was a somewhat crude initial effort at verbal) IQ, and full-scale (total) IQ. Second, Wechsler tice, enthusiasm, and espe- measuring mental ability. He revised it in 1908 and discarded the intelligence quotient in favour of a new cially with method one can scoring scheme based on the normal distribution. This succeed in increasing one’s again in 1911. Unfortunately, his revising came to an attention, memory, judg- abrupt end with his death in 1911. However, other scoring system has since been adopted by most other ment, and in becoming psychologists continued to build on Binet’s work. IQ tests, including the Stanford-Binet. Although the literally more intelligent In the United States, Lewis Terman and his col- term intelligence quotient lingers on in our vocabulary, than one was before.” leagues at Stanford University soon went to work on scores on intelligence tests are no longer based on an a major expansion and revision of Binet’s test. Their actual quotient (Urbina, 2011). work led to the 1916 publication of the Stanford- Binet Intelligence Scale (Terman, 1916). This revi- The Debate about the Structure sion was quite loyal to Binet’s original conceptions. of Intelligence The Drs. Nicholas and Dorothy Cummings Center for the History However, it incorporated a new scoring scheme based on William Stern’s “intelligence quotient” (Weiner, The first half of the 20th century also witnessed a long- 2013b). An intelligence quotient (IQ) is a child’s running debate about the structure of intellect. The mental age divided by chronological age, multi- debate was launched by Charles Spearman. He was of Psychology, The University of Akron. plied by 100. IQ scores originally involved actual a British psychologist who invented a complicated quotients, calculated as follows: statistical procedure called factor analysis. In factor analysis, correlations among many variables are Mental age analyzed to identify closely related clusters of vari- IQ 5 3 100 Chronological age ables. If a number of variables correlate highly with The IQ ratio placed all children (regardless of age) one another, the assumption is that a single factor is on the same scale, which was centred at 100 if their influencing all of them. Factor analysis attempts to mental age corresponded to their chronological age identify these hidden factors (Gorsuch, 1983). DAVID WECHSLER (see Table 9.1 for examples of IQ calculations). Spearman (1904, 1927) used factor analysis to “The subtests [of the WAIS] Terman’s technical and theoretical contribu- examine the correlations among tests of many spe- are different measures tions to psychological testing were modest. Yet he cific mental abilities. He concluded that all cognitive of intelligence, not mea- made a strong case for the educational benefits of abilities share an important core factor. He labelled sures of different kinds of intelligence.” testing and became the key force behind American this factor g for general mental ability. Spearman rec- schools’ widespread adoption of IQ tests. As a result ognized that people also have “special” abilities (e.g., of his efforts, the Stanford-Binet quickly became the numerical reasoning or spatial ability). However, he Table 9.1 CALCULATING THE INTELLIGENCE QUOTIENT MEASURE CHILD 1 CHILD 2 CHILD 3 CHILD 4 Mental age (MA) 6 years 6 years 9 years 12 years Chronological age (CA) 6 years 9 years 12 years 9 years MA 6 6 9 12 IQ 5 3 100 3 100 5 100 3 100 5 67 3 100 5 75 3 100 5 133 CA 6 9 12 9 Intelligence and Psychological Testing 333 02940_ch09_ptg01.indd 333 20/01/21 7:39 PM  Figure 9.2 g factors called primary mental abilities: word fluency, Spearman’s g. In his analysis verbal comprehension, spatial ability, perceptual of the structure of intellect, Charles Spearman found speed, numerical ability, inductive reasoning, and that specific mental talents S1 memory. Following in this tradition, J. P. Guilford (S1, S2, S3, and so on) were (1959, 1985) extended this reasoning. Guilford’s highly intercorrelated. Thus, he theory divided intelligence into 150 separate abilities concluded that all cognitive abilities share a common core, and did away with g entirely (see Figure 9.3). which he labelled g for general The debate about the nature structure of intel- mental ability. ligence continued for many decades and in some Source: From Weiten. Cengage Advantage Books: Psychology, 9E. © 2013 South-Western, respects the issue lingers even today (e.g., Rinaldi et a part of Cengage, Inc. Reproduced by permis- al., 2017; Savi et al., 2019). Paradoxically, both views sion. www.cengage.com/permissions of the structure of intellect have remained influ- S3 ential. Armed with computers, modern researchers S2 using enhanced approaches to factor analysis have shown again and again that batteries of cognitive tests are highly intercorrelated, as Spearman had sug- thought that individuals’ ability in these specific gested (Brody, 2005; Carroll, 1996; Gottfredson, 2009; areas is largely determined by their general mental Jensen, 1998). Today, researchers interested in the ability (see Figure 9.2). nature, determinants, and correlates of intelligence are A very different view of the structure of intel- still examining research evidence focused on under- lect was soon proposed by L. L. Thurstone. He standing the structure of intelligence, often employing was an American psychologist who developed the sophisticated technology only recently developed. test that evolved into the Scholastic Aptitude Test (SAT; Our Featured Study for this chapter is one example Jones, 2000). Using a somewhat different approach of this research. Conducted at Western University, it to factor analysis, Thurstone (1931, 1938, 1955) con- employed both traditional types of cognitive tests and cluded that intelligence involves multiple abilities. models of brain functional intelligence. Thurstone argued that Spearman and his followers placed far too much emphasis on g. In contrast, Thurstone carved intelligence into seven independent FEATURED STUDY Fractioning human intelligence. Operations Con ver Description Div gen Eva erg t pr lua Contents In this study the authors evaluate the hypothesis that ent odu tion ual y pro ction Vis tor human intelligence is composed of several types duc udi ic tion A bol of intelligence, each of which is related to a distinct Me Sym ant ic Cog mo al functional neural network. niti ry Sem our on havi B e Investigators Hampshire, A., Highfield, R., Parkin, B., & Owen, A. M. Units (2012). Neuron, 76(6), 1225–1237. Classes Relations In the 1980s, the developers of IQ tests began Products moving in the opposite direction, from a focus on Systems a single indicator of IQ to multiple indicators. Their Transformations motivation was to give clinicians, educators, and school systems more information (than a single, global Implications score) that could better aid them in the diagnosis of learning disabilities and the evaluation of chil- dren’s potential. New developments in intelligence research and theory captured by hierarchical models of intelligence proved useful. In hierarchical models of Figure 9.3 intelligence, intelligence is viewed as best represented Guilford’s model of mental abilities. In contrast to Spearman (see Figure 9.2), J. P. Guilford as a series of layers or strata with general intelligence, concluded that intelligence is made up of many separate abilities. According to his analysis, we may have as many as 150 distinct mental abilities that can be characterized in terms of the g, at the top. As you move down the hierarchy, at operations, contents, and products of intellectual activity. each successive layer intelligence is subdivided into 334 CHAPTER 9 02940_ch09_ptg01.indd 334 08/01/21 9:32 PM  more specific abilities. For example, one model of test to test. These variations depend on whether intelligence proposed that g should be divided into the test is intended for children or adults (or both) fluid intelligence and crystallized intelligence (Carroll, and whether the test is designed for individuals or 1993; Cattell, 1963; Horn, 1985; Stanovich et al., groups. Overall, the questions are fairly diverse in 2011, 2016). Fluid intelligence involves reasoning format. The Wechsler scales are among the most ability, memory capacity, and speed of information widely used IQ tests. Currently, there are three scales, processing. Crystallized intelligence involves ability each adapted to specific age groups: the Wechsler to apply acquired knowledge and skills in problem Preschool and Primary Scale of Intelligence (Fourth solving. Recent work in this area suggests that the Edition: WPPSI-IV), the Wechsler Intelligence prefrontal cortex is more involved in problem solving Scale for Children (Fifth Edition: WISC-V), and the accessing fluid intelligence but less involved in tasks Wechsler Adult Intelligence Scale (Fourth Edition: implicating crystallized intelligence (Nisbett et al., WAIS-IV). The Wechsler scales, with their numerous 2012). The initial distinction between fluid and crys- subtests, provide a representative example of the tallized intelligence led to further efforts to break g kinds of items that appear on most IQ tests. The 4th into basic components. edition of the WAIS scale was published in 2008. In One of the most influential of these hierarchical addition to a full-scale IQ score, the test provides models is that proposed by John Carroll (1993). His separate tests and scores for verbal comprehension, model was based on a psychometric analysis of hun- perceptual reasoning, processing speed, and working dreds of studies of intelligence. In his model, intelli- memory. Each of these four major scales is composed gence is represented in three strata, with g at the top of specific core subtests. For example, the core sub- (Stratum I), eight broad abilities such as crystallized tests for verbal comprehension consist of vocabulary, and fluid intelligence (referred to as Gf and Gc) in the information, and similarities and the subtests for middle layer (Stratum II), and more specific abilities working memory include digit span and arithmetic. such as spelling at the bottom (Stratum III). Carroll’s As you can see in Figure 9.4, items in the Wechsler eight mid-level abilities include, in addition to crys- subtests require participants to furnish informa- tallized and fluid intelligence, broad abilities such as tion, recognize vocabulary, and demonstrate basic visual perception and auditory perception, learning memory. Generally speaking, examinees are required and memory, cognitive speediness, processing speed, to manipulate words, numbers, and images through and retrieval ability. abstract reasoning. Contemporary IQ tests generally are based on a hierarchical model of intelligence, which subdivides Broadening the Concept of Intelligence g into a number of specific abilities. For example, As we have seen, interest in developing reliable and the current version of the Stanford-Binet includes valid measures and a concern with the structural ten subtests, and the WAIS-IV includes ten core nature of intelligence has had a prominent place in and five supplemental subtests. The nature of the the history of modern psychology. Many of these questions found on IQ tests varies somewhat from developments are based on psychometric analyses Figure 9.4 Wechsler Adult Intelligence Scale (WAIS IV) Subtests on the Wechsler Adult Intelligence Scale Subtest Description Example (WAIS-IV). The WAIS-IV con- tains a number of subtests, Information Taps general range of information On what continent is France? and is designed for use with Arithmetic Tests arithmetic reasoning through verbal problems How many hours will it take to drive 150 kilometres at individuals from ages 16 50 kilometres per hour? to 90. Scales yield separate scores for verbal compre- Similarities Asks in what way certain objects or concepts are How are a calculator and a typewriter alike? hension, working memory, similar; measures abstract thinking perceptual reasoning, and Digit span Tests attention and rote memory by orally presenting Repeat the following numbers backward: 2 4 3 5 1 8 6 processing speed. Some of series of digits to be repeated forward or backward the subtests are shown here, along with examples of low- Vocabulary Tests ability to define increasingly difficult words What does audacity mean? level (easy) test items that closely resemble those on the Block design Tests ability to perceive and analyze patterns by Assemble blocks to match this design: WAIS-IV. presenting designs that must be copied with blocks Intelligence and Psychological Testing 335 02940_ch09_ptg01.indd 335 08/01/21 9:32 PM  and IQ (Gignac & Bates, 2017). Thus, it appears that 1.8 larger brains are associated with greater intelligence, but the association is modest. 1.6 One obvious implication of these findings on brain size and intelligence eagerly embraced by those 1.4 who tout the influence of heredity on intelligence 1.2 is that genetic inheritance gives some people larger Relative mortality rate brains than others and that larger brain size promotes 1.0 greater intelligence (Rushton, 2003). However, as 0.8 always, we must be cautious about interpreting cor- relational data. As discussed in Chapter 3, research 0.6 has demonstrated that an enriched environment can 0.4 produce denser neural networks and heavier brains in laboratory rats (Rosenzweig & Bennett, 1996). 0.2 Thus, it is also possible that causation runs in the 0 opposite direction—that developing greater intelli-