THE MEASUREMENT OF INDIVIDUAL DIFFERENCES

ABOUT THE COURSE

• The course consists of FOUR lectures.

• There will be ONE question on this course in the degree examination.

• As with the Methodology lectures, I shall try to put the file on the Web before each lecture.

The examination

• Consists of questions that require short answers.• The optimal strategy is to devote equal amounts of time

to the questions. That means you have SEVEN AND A HALF MINUTES PER QUESTION!

• To do yourself justice, you must PRACTISE WRITING SHORT ANSWERS.

• At the end of each lecture, I shall provide you with a practice question, WHICH I URGE YOU TO ATTEMPT when you have a few minutes to spare.

• Don’t forget to stick rigidly to the time limit!

Lecture 1

MEASURING THE DIMENSIONS OF MIND

How? The search for mechanisms

• How does the brain work? How are memory functions delivered? How do we solve problems and reason?

• Much experimental psychological research is concerned with discovering the mechanisms by which functions such as memory, reasoning and language are delivered.

The caffeine experiment

• We may obtain evidence that caffeine improves performance. But the best performer may be in the Placebo group; and the worst may be in the Caffeine group.

• Individual differences tend to obscure the patterns we seeking.

Permanent, pervasive characteristics

• But individual differences are surely more than just nuisance factors that inflate the denominators of t-tests and force us to test large numbers of participants.

• In the first place, aptitudes for or difficulties with various tasks tend to be ENDURING ASPECTS of a person’s makeup. The person who achieved the highest score in the caffeine experiment would probably achieve high scores in other experiments on skilled performance; the lowest scorers are likely to get low scores on other tests of skill.

• Other qualities, such as political attitudes and extraversion, are also likely to be PERMANENT and PERVASIVE characteristics.

How much? Differential psychology

• DIFFERENTIAL PSYCHOLOGY is the systematic study of individual differences.

• What are the most important psychological dimensions on which people vary?

• How can we measure a person’s position on such a dimension?

• Why do people vary on these dimensions?

Psychological testing

The principal research instrument of the differential psychologist is the PSYCHOLOGICAL TEST, which often takes the form of a questionnaire. (Not all psychological tests are questionnaires, however.)

Psychometrics

• The development of psychological tests and measurements is known as PSYCHOMETRICS.

• In this course of lectures, I shall be concerned primarily with the general psychometric principles governing the construction of psychological tests.

Scholastic aptitude

• Every teacher will agree upon two things.1. Some children have great difficulty in learning school

subjects.2. This difficulty is experienced whatever the subject. The

child who has difficulty with French is likely also to have difficulty with mathematics. On the other hand, the child who enjoys mathematics is also likely to thrive on French, geography, history and other school subjects.

• Children tend to achieve similar PERCENTILES in their

various school examinations. It’s highly unusual to find a child at the top of the class in mathematics, yet at the bottom in French.

Alfred Binet

• Alfred Binet was a French educational psychologist, working early in the 20th century.

• He was concerned by the number of children who were failing to benefit from their schooling and sought ways of improving the situation.

• A first step, he believed, was to find a way of measuring scholastic aptitude.

A landmark in educational history

• In 1904, a committee was set up by the Parisian minister of public instruction to identify children in need of remedial education.

• On the committee were Alfred Binet and his medical associate Theodore Simon.

• Binet and Simon produced the first intelligence test in 1905.

Intelligence

• ‘Intelligence is ….’ There have been many definitions of intelligence.

• ‘the capacity to reason well, to judge well and to comprehend well’ (Binet & Simon, 1916; p.92).

• ‘So-called “intelligence tests” are primarily measures of the ability to succeed in school-type tasks’ (Aiken, 1976; p.148).

The first intelligence test (1905)

• This test was designed to be INDIVIDUALLY administered. Later, GROUP TESTS were developed.

• There were 30 problems, arranged in order of increasing difficulty.

• The problems were not directly about PARTICULAR school subjects. They were designed to test the child’s judgment, understanding and reasoning, which are qualities Binet believed to be necessary for the learning of ANY school subject.

Avoidance of school knowledge

‘It is the intelligence alone that we seek to measure, by disregarding in so far as possible the degree of instruction which the child possesses … We give him nothing to read, nothing to write, and submit him to no test in which he might succeed by means of rote learning’ (Binet & Simon, 1905).

Three simple figures

Reproducing a figure from memory

• In Binet’s figure-copying test, the child is shown one of the three figures; then the shape is removed and the child is asked to draw it from memory.

• Although they are all simple figures, Binet considered that it would be more difficult to draw the diamond from memory than the square; and the most difficult of all would be the cylinder.

The need for normative data

• To assess one child’s performance, we need to know how a TYPICAL child of the same age would perform.

• What is needed is a knowledge of the responses of a large number of children in the same age group to the same problem.

• No such NORMATIVE DATA were available with the first intelligence test, so it was difficult to assess a child’s performance.

Binet’s age norms

• Binet and his associates collected the first set of AGE NORMS for children’s performance.

• Sets of test items were produced which could be solved by children of a specific age and above, but were difficult for most children below that age.

• In this way, the data identified sets of test items that could differentiate typical eight-year-olds from typical seven-year-olds, typical nine-year-olds from typical eight-year-olds and so on.

Age norms: Reproducing a figure from memory

• A 5-year-old can copy a square from memory, but not a diamond or a cylinder.

• An 8-year-old can copy a square and a diamond, but not a cylinder.

• An 11-year-old can copy all three figures.

Binet’s 1911 age scale

• There were 30 items in Binet’s first (1905) test.

• There were 54 items in Binet’s final (1911) test.

• These included some items that Binet thought were suitable for adults.

Selected items from the 1911 test

• When the final Binet test appeared in 1911, the items it contained discriminated between typical children in different age groups.

• A few examples will illustrate this DISCRIMINATIVE PROPERTY.

Age 3

• Points to nose, eyes and mouth.

• Repeats two digits.

• Enumerates the objects in a picture.

• Gives the family name.

• Repeats a sentence of six syllables.

Age 4

• Gives own sex.

• Names key, knife and penny.

• Repeats three digits.

• Compares two lines.

The discriminative property

• Typical 3-year-olds could not give their own sex, name the three objects, repeat three digits or compare two lines. Typical 4-year-olds could do all three things.

• Those items, therefore, discriminated between typical 3-year-olds and typical 4-year-olds.

Age norms are anchored in historical time and place

• Binet’s age norms were true of typical French children living around Paris early in the 20th century.

• They do not necessarily apply to 21st century children living in another country.

• In fact, there is evidence that performance norms have changed over the generations, even in one particular country.

Age 10

• Arranges five blocks in order of weight.

• Copies two drawings from memory.

• Criticizes absurd statements.

• Answers or comprehends ‘difficult questions’.

• Uses three given words in not more than two sentences.

Age 12

• Resists suggestion as to lengths of lines.

• Composes one sentence containing three given words.

• Names 60 words in 3 minutes.

• Defines three abstract words.

• Discovers the sense of a disarranged sentence.

The discriminative property

The typical 10-year-olds Binet studied could not resist suggestion, could not compose a sentence containing three given words, couldn’t name 60 words in three minutes, couldn’t define three abstract words, and couldn’t discover the sense of a disarranged sentence. The typical 12-year-olds could do all these things.

Mental age

• A person’s MENTAL AGE is the chronological age at which most children can perform at the same level as the person tested.

• A child is usually 11 before he or she can draw a cylinder.

• So if a child of 9 years of age can draw the cylinder, he or she is two years in advance of most children and has a mental age of 11 years; whereas a child aged 12 years who can only draw the diamond has a mental age of 8 years.

Binet’s assumptions

• Binet and Simon believed that, underlying a child’s difficulty with school subjects was a more general problem.

• They assumed that such children lacked certain general reasoning and judgmental abilities that were required in order to learn ANY school subject, despite the obvious differences among subjects such as mathematics, Geography and French.

• Their questions and tasks were intended to tap these supposed basic abilities.

Hypothetical constructs

• Binet was attempting to measure a HYPOTHETICAL PSYCHOLOGICAL DIMENSION of scholastic aptitude, which he believed to underlie performance in any school subject. Such general scholastic aptitude, or ‘intelligence’ is an example of a HYPOTHETICAL CONSTRUCT.

• Other well known hypothetical constructs in psychology are EXTRAVERSION, FIELD DEPENDENCE-INDEPENDENCE and NEUROTICISM.

Note

• Binet was an educationist, concerned with educational problems, such as the identification of children in difficulties with their education.

• Since he was acutely aware of how little was known about the learning process, he was very cautious in his own use of language. He himself avoided the term ‘mental age’, preferring what he felt to be the more neutral term ‘mental level’. The term ‘mental age’, however, soon gained currency after his untimely death in 1911.

The first test of mental age

• In the third and last version of the Binet test (1911), which was published after his death, the concept of mental age was introduced for the first time.

• The availability of the age norms increased the usefulness of the test enormously.

The intelligence quotient (IQ)• In 1912, the German psychologist Stern proposed, as a measure of

intelligence, the INTELLIGENCE QUOTIENT (IQ).• Those whose mental ages exceeded their chronological age would

have IQs greater than 100• Those whose mental ages were less than their chronological ages

would have IQs less than 100.• Those whose with equal mental and chronological age would have

IQs near to 100.

The Stanford-Binet test

The first intelligence test to measure IQ was first published in 1916 at Stanford University in the US by Lewis Terman.

Distribution of IQ

• The pioneers of intelligence research were convinced that this quality, like physical attributes such as height or weight, must have an approximately normal distribution.

• The Stanford-Binet test was so constructed that IQ had an approximately normal distribution with a mean of 100 and an SD of 15.

15-year-old versus adult

15-YEAR-OLD

• Repeats seven digits.• Finds three rhymes for a given

word in one minute.• Repeats a sentence of 26

syllables.• Interprets pictures.• Interprets given facts.

ADULT

• Solves the paper-cutting test.• Rearranges a triangle in

imagination.• Gives differences between

pairs of abstract terms.• Gives three differences

between a president and a king.

• Gives the main thought of a selection that he has read.

Notice …

• No one questions the claim that adults can do many things that 15-year-old children cannot.

• Life experience enables the typical adult to perform many tasks of a reasoning or judgmental nature that the brightest 15-year-old could not perform.

• Binet’s list exemplifies such tasks.

However…

• The tasks that Binet used for the typical adult are of a nature somewhat different than those used for children: there is a new emphasis upon knowledge – albeit wordly knowledge rather than schoolwork.

• In fact, it has proved to be impossible to find a set of relatively knowledge-free tasks that adequately discriminates between the typical 15-year-old and the typical sixteen-year old.

• MENTAL AGE DOES NOT INCREASE BEYOND 15 YEARS!

The problem with mental age

• Mental age (and IQ as defined by Stern) make sense and work well with children.

• But it seemed desirable to extend the concept of IQ to the adult population as well.

• Unfortunately it turned out that mental age does not increase beyond 15 years.

• So, according to Stern’s formula, one’s IQ would decline steadily throughout one’s adult life.

The problem with Stern’s IQ

If mental age does not increase beyond 15, the value of (MA/CA)×100 will decline as the person ages.

The problem with Stern’s IQ

The deviation IQ

• Because of the difficulty with Stern’s definition, IQ was later redefined in terms of performance of adults in the various age bands.

• IQ has a normal distribution with a mean of 100 and a standard deviation of 15.

• So if a person scores at the 97.5th percentile in relation to people in their own age band, they have an IQ of 130.

• This is known as a DEVIATION IQ. • NOTE that the deviation IQ isn’t a QUOTIENT at

all.

The Wechsler Tests

• The Stanford-Binet (through various revisions) has never been regarded as a satisfactory test of adult intelligence.

• In 1939, David Wechsler, a psychologist at Bellevue Hospital in New York, designed an individual test specifically for adults.

• His test is known as the Wechsler Adult Intelligence Scale (WAIS).

• The WAIS embodies the deviation IQ, rather than the IQ as defined by Stern.

The WAIS items

1. Information.2. Picture Completion.3. Digit Span.4. Picture arrangement.5. Vocabulary.6. Block Design.7. Arithmetic.8. Object Assembly.9. Comprehension.10.Digit Symbol.11.Similarities.

The measures

• The WAIS yields three IQ measures: (1) Verbal, (2) Performance and (3) Full Scale.

• These are all deviation IQs, expressed on a scale with a mean of 100 and an SD of 15.

A new emphasis

• As a clinician, Wechsler was more interested in the patient’s PERFORMANCE PROFILE, rather than summary measures of a person’s ability to act purposively, think rationally and deal effectively with the environment.

• A marked difference in Verbal and Performance IQs, for example, may indicate brain damage.

Other hypothetical constructs

• Intelligence was the first dimension of the mind that psychologists attempted to measure.

• Dimensions of personality have also been investigated, such as the ‘Big Five’ described in the Five-Factor Model proposed by Goldberg (1981) and investigated empirically by McCrae & Costa (1987).

The Big Five

1. Extraversion

2. Agreeableness

3. Conscientiousness

4. Neuroticism

5. Openness to Experience

Independent?

• For many years, some have argued that cognition and personality are not separate aspects of mental life.

• They have claimed that, just as a person may be socially extraverted, a person has a characteristic way of thinking, over and above general intellectual level.

• If, when you are exploring the Internet with a search engine such as Google, you type ‘cognitive style’, you will find a large body of literature describing many different stylistic dimensions.

Field dependence

• The most well-established dimension of cognitive style is FIELD-DEPENDENCE, which was proposed and researched by Herman Witkin and his team in the nineteen forties, fifties and sixties (e.g. Witkin, 1962).

• Witkin and his associates have made perhaps the strongest case for the existence of a dimension over and above the well-established Big Five or intelligence.

Cognitive styles

‘Recent research has demonstrated that people show characteristic, self-consistent ways of functioning in their perceptual and intellectual activities. These cognitive styles, as they have come to be called, appear to be manifestations, in the cognitive sphere, of still broader dimensions of personal functioning which cut across diverse psychological areas’ (Witkin, 1965).

Witkin’s field theory

• Witkin used the ‘field’ metaphor (which comes from Gestalt psychology) to refer to any situation in which a person is required to solve a problem.

• A field can be broken up, or ‘articulated’ into constituent ‘elements’, which can be reassembled or re-grouped to solve the problem.

• People vary enormously in their ability to do this.

The Rod-and-Frame Test (RFT)

• You are sitting in a darkened room.

• All you can see is a luminous, tilted frame, inside which is a movable luminous rod.

• You are asked to adjust the position of the rod so that (unlike the frame) it is truly vertical.

• Some people align the rod with the frame, insisting that it is vertical.

• Others align the rod with the true vertical.

Starting position

Correct alignment of rod with vertical

Field-dependent alignment of rod with the axis of the tilted frame.

The field

• In the Rod-and-frame test, the visual elements of the ‘field’ are the rod and the frame.

• But there is also a proprioceptive element, namely, the FELT POSITION OF ONE’S OWN BODY, which tells the person about the ‘upright’ orientation.

• The field-independent person can compare the rod and the frame independently with felt body position and adjust the rod correctly.

• For the field-dependent person, frame orientation and rod orientation are fused, so that the person cannot manipulate the rod independently and compare it with felt body position.

Field dependence-independence

• On the left is the starting position of the rod and frame.• In the middle is a FIELD-INDEPENDENT performance.• On the right is a FIELD-DEPENDENT performance.

The embedded figures test

• In the EMBEDDED FIGURES TEST (EFT), you are asked to find the simple shape on the right in the more complex figure on the left.

• Some see it instantly; others find it very difficult to see. Most of us fall somewhere in between these extremes.

The Body Adjustment Test

• In the Body Adjustment Test (BAT), you are placed in a tilted room, seated on a tilting chair which you can adjust. Your task is to make your chair truly upright.

• Some can do this perfectly; but others insist that the chair is truly vertical when it is actually aligned with the room.

• Most of us fall somewhere in between.

Field Dependence-Independence

• Witkin believed that all three tasks tapped the same underlying ability.

• The person who performs well in such tasks can analyse the total field of experience into its component parts and manipulate the parts independently of the overall organisation to solve the problem.

• Here the ‘field’ can be purely visual, as in the EFT, or visual and proprioceptive, as in the RFT or the BAT.

Witkin’s evidence

• The ability to analyse the total field into its component parts is a HYPOTHETICAL CONSTRUCT.

• To support his claim that there is such an ability, Witkin reported that there were substantial POSITIVE CORRELATIONS among the EFT, BAT and RFT tests.

• The person who adjusts the rod to the true vertical can also make the chair upright and quickly spot the embedded figures. The person who cannot spot the embedded figure insists that the rod is vertical when it’s actually aligned with the long axis of the frame and claims that a chair is truly upright when it is actually aligned with the tilted room.

Issues

• We have intelligence already. Do we really need another dimension of ability to explain individual differences in performance?

• Could so-called field dependence-independence simply be intelligence?

• Witkin was aware of this problem and presented evidence to support his claim that field dependence-independence is not synonymous with intelligence.

• I shall consider that evidence later, when I describe how the CONSTRUCT VALIDITY of a test can be demonstrated.

Summary

• Today, I introduced two psychological dimensions: 1. intelligence and 2. field-dependence-independence.

• Both dimensions are hypothetical constructs. • I discussed how Binet attempted to measure

‘intelligence’, conceived as the ability to learn school subjects.

• I discussed some of the evidence that Witkin advanced in support of his claim that there are individual differences in what he termed ‘cognitive style’, namely the dimension of field-dependence-independence.

This week’s question

What was Stern’s definition of an IQ? In your answer, explain the concept of mental age. What was the major drawback with the measure that Stern proposed?