THE MEASUREMENT OF INDIVIDUAL DIFFERENCES

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THE MEASUREMENT OF INDIVIDUAL DIFFERENCES
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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.

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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.
• Dont forget to stick rigidly to the time limit!

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Lecture 1MEASURING THE DIMENSIONS OF
MIND
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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.

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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.

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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 persons 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.

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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 persons position on such a
  dimension?
• Why do people vary on these dimensions?

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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.)

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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.

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Scholastic aptitude

• Every teacher will agree upon two things.
• Some children have great difficulty in learning
  school subjects.
• 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. Its highly
  unusual to find a child at the top of the class
  in mathematics, yet at the bottom in French.

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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.

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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.

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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).

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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
  childs judgment, understanding and reasoning,
  which are qualities Binet believed to be
  necessary for the learning of ANY school subject.

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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).

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Three simple figures
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Reproducing a figure from memory

• In Binets 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.

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The need for normative data

• To assess one childs 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 childs performance.

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Binets age norms

• Binet and his associates collected the first set
  of AGE NORMS for childrens 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.

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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.

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Binets 1911 age scale

• There were 30 items in Binets first (1905) test.
• There were 54 items in Binets final (1911) test.
• These included some items that Binet thought were
  suitable for adults.

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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.

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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.

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Age 4

• Gives own sex.
• Names key, knife and penny.
• Repeats three digits.
• Compares two lines.

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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.

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Age norms are anchored in historical time and
place

• Binets 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.

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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.

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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.

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The discriminative property

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

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Mental age

• A persons 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.

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Binets assumptions

• Binet and Simon believed that, underlying a
  childs 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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.
• Binets list exemplifies such tasks.

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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!

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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 Sterns formula, ones IQ would
  decline steadily throughout ones adult life.

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The problem with Sterns IQ

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

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The problem with Sterns IQ
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The deviation IQ

• Because of the difficulty with Sterns
  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 isnt a QUOTIENT at
  all.

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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.

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The WAIS items

• Information.
• Picture Completion.
• Digit Span.
• Picture arrangement.
• Vocabulary.
• Block Design.
• Arithmetic.
• Object Assembly.
• Comprehension.
• Digit Symbol.
• Similarities.

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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.

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A new emphasis

• As a clinician, Wechsler was more interested in
  the patients PERFORMANCE PROFILE, rather than
  summary measures of a persons 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.

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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).

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The Big Five

• Extraversion
• Agreeableness
• Conscientiousness
• Neuroticism
• Openness to Experience

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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.

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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.

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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).

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Witkins 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.

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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.
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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 ONES 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.

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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.

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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.

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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.

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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.

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Witkins 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 its 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.

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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.

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Summary

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

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This weeks question

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