Outline

1
Outline

• David Wechsler some history
• Wechslers Scales
• IQ scores
• Index scores
• Verbal subtests
• Performance subtests
• WAIS Psychometrics

2
David Wechsler (1896 1981)

• Studied at Columbia University (M.A., 1917
  Ph.D., 1925)
• Went to France with US Army in 1919, then to
  London
• Studied with Pearson Spearman
• Also with Anna Freud in Vienna

3
David Wechsler

• Worked at NYs Bellevue Hospital.
• Unhappy with the Stanford-Binet
• Content appropriate only for children
• Rapport problems if used with adults
• Produces only a single score
• Norms not appropriate for adults
• Binets emphasis on speed hurt older adults
  scores

4
Wechsler Scales

• 1939 the Wechsler-Bellevue, later called the
  WAIS.
• 1945 the Wechsler Memory Scale
• 1949 the childrens version, the WISC
• 1955 Wechsler Adult Intelligence Scale
• 1967 the WPPSI for children ages 2½ -7
• 1981 WAIS-R (revised form of 1955 test)
• 1997 WAIS-III

5
Wechsler Scales

• Intelligence is the aggregate or global capacity
  of the individual to act purposefully, to think
  rationally and to deal effectively with his
  environment.
• David Wechsler (1939)
• global one score ultimately describes a
  persons intellectual ability
• aggregate that one score is composed of a
  number of sub-scores

6
Wechslers original test

• Wechsler believed that intellectual ability
  involves two major types of skills verbal and
  performance abilities.
• Each of these broad types includes a variety of
  specific skills that are assessed by the various
  subtests of the WAIS.
• However, all these subtests measure g as well as
  specific skills

7
(No Transcript)
8
Wechsler test produced 3 IQ scores

• Full-scale IQ

• reflects both verbal and performance IQs
• most reliable and valid score extracted from WAIS
• why do you think this is the most reliable?

9
Wechsler test produced 3 IQ scores

• Verbal IQ

• Responses require person being tested to use
  language to understand instructions or to make
  a response

10
Wechsler test produced 3 IQ scores

• Performance IQ

• Performance subtests involve doing something, not
  just answering questions

11
Structure of the WAIS

• WAIS-III has four index scores
• verbal comprehension
• working memory
• perceptual organization
• processing speed.
• Index scores added recently because, with new
  subtests, factor analysis suggests these four
  factors

12
Index scores

• Verbal comprehension

• assesses general verbal skills, such as verbal
  fluency, ability to understand and use verbal
  reasoning, and verbal knowledge
• based on both formal and informal educational
  opportunities,

13
Index scores

• Working memory
• The blackboard of the mind (Goldman-Rakic, 1992)

• Encode information into STM, store it there,
  retrieve it when needed
• Manipulate information (e.g., addition)
• Thinking, learning, planning

14
Index scores

• Perceptual organization

• Use visual, spatial, and visually-guided motor
  skills
• Organize thoughts
• Assesses comfort with new, unfamiliar situations

15
Index score

• Processing speed
• The speed at which cognitive processes can be
  carried out

• focus, scanning speed, sequentially ordering
  visual information
• sensitive to motivation, difficulty working under
  time pressure.
• biological
• cultural factors have little impact

16
WAIS Verbal Tests

• Vocabulary
• Similarities
• Arithmetic
• Digit Span
• Information
• Comprehension
• Letter-Number Sequencing

17
Vocabulary

• Subject is given one word at a time, asked to
  define it
• Sensitive to word knowledge, linguistic
  development, acquired knowledge, verbal
  expression ability, crystallized intelligence

• The best single measure of g
• Correlation of vocabulary score with g is .83

18
Vocabulary

• Very stable
• Resistant to effects of poor concentration in
  schizophrenia
• Not affected by mild concentration trouble

• Of all WAIS subtests, the one most resistant to
  brain damage
• Thus, allows a good estimate of pre-morbid
  functioning

19
Similarities

• Task is to say how two (superficially) dissimilar
  items might be similar
• Evaluating details which details are
  diagnostic?

• Earlier items in series are known through
  experience (e.g., In what way are a cake and a
  pudding alike?)
• Later items require abstract thinking (e.g., How
  are affection and approval alike?

20
Similarities

• Logical, abstract thinking
• Concept formation
• Crystallized and fluid intelligence

• With Information subtest, the second best for
  measuring g
• Correlation with g .79

21
Similarities

• Of VCI (Verbal Comprehension Index) subtests, the
  one least affected by formal education or learning

• Score on this subtest is impacted by
  psychopathology, and by brain damage esp. left
  hemisphere lesions

22
Arithmetic

• Assesses working memory, numerical reasoning,
  computation skill, concentration, retrieval from
  LTM
• Influenced by emotional state

• Correlation with g is r .75

23
Digit Span

• Repeat a series of up to 7 digits in correct
  order
• Digits presented 1 per second
• Tested both Forward (DSF) and Backward (DSB)

• Attention, auditory memory and sequencing, short
  term memory, mental alertness, sequential
  processing, cognitive flexibility

24
Digit Span

• Average 6.4 digits forward, 4.7 backwards
• DSF DSB 5 suggests brain damage

• Correlation with g r.57 (the worst)

25
Information

• Acquired knowledge, crystallized intelligence,
  fund of information, range of general factual
  knowledge, long term memory
• Affected by formal education opportunities

• Correlation with g r .79 (2nd best)
• Failure on easy items followed by success on
  harder items suggests retrieval difficulties
• Resistant to psychopathology and brain damage
  good estimate of pre-morbid functioning

26
Comprehension

• 3 different kinds of questions
• Appropriate responses to hypothetical situations
• Logical explanations for everyday actions
• Proverb interpretations

• Assesses social and moral reasoning, judgment,
  verbal concepts, knowledge of ordinary standards
  of behavior, practical information

27
Comprehension

• Rewards conventional responses, not creative ones
• R Hem patients may score high (their L Hem intact
  so they know answers) but still behave
  inappropriately

• g correlation r .77

28
Letter-number sequencing

• Optional not needed to compute IQ
• Task is to re-order intermixed,
  randomly-sequenced numbers and letters
• Taps STM, sequential reasoning ability, planning

• g correlation r .65
• Impaired by anxiety, weak attention focusing
  ability
• Dropping a letter attention problem
• Mixing up letters sequencing problem

29
WAIS Performance Tests

• Picture completion
• Digit symbol-coding
• Block design
• Matrix reasoning
• Picture arrangement
• Symbol search (optional)
• Object assembly (optional)

30
Picture Completion

• Task say what detail is missing from a picture.
• Timed response
• Pointing response is allowed
• Raises issue of pointing precision (trained
  examiner required)

• Alertness, attention to detail
• LTM (Visual)
• Crystallized intelligence
• R Hem skill
• g correlation r .64

31
Digit Symbol Coding

32
Digit Symbol Coding

• Visual STM
• Psychomotor speed
• Visual-motor coordination
• Visual sequencing
• Accuracy speed

• g correlation r .59
• Very sensitive to any kind of brain damage

33
Block Design

• Assesses visual-motor coordination, visual
  analysis synthesis, spatial visualization
• Visual input, motor output
• Fluid intelligence
• Trial error learning

• g correlation .72
• Affected by R Hem damage
• Bizarre solutions may indicate dementia

34
Matrix Reasoning

• 4 types of stimuli
• pattern completion
• classification
• analogy
• serial reasoning
• Subject given a series of matrices and must say
  what goes in the empty cell

?
O
o
O
35
Matrix reasoning

• Measures abstract thinking, nonverbal reasoning,
  analogy skill
• Fluid intelligence
• Visual organization

• g correlation r .72

36
Picture Arrangement

• Task is to put a series of (randomly-ordered)
  pictures into narrative order (so they tell a
  coherent story)
• As if you found a comic strip jumbled up and had
  to order the frames sensibly

• Non-verbal reasoning
• Possibly social skill
• Fluid crystallized intelligence
• Planning
• Time concepts

37
Picture Arrangement

• Failure may be due to visual problems (compare
  with Picture Completion)

• g correlation r .66

38
Symbol Search

• Optional not needed to compute IQ
• Subject shown two target abstract symbols and
  asked whether either target appears in a set of
  probe symbols

• 120 seconds allowed
• How many can subject do in that time?

39
Symbol Search

• Visual-motor coordination and speed, planning,
  STM, perceptual speed
• Large practice effects in young adults

• g correlation r .70

40
Object Assembly

• Subject given pieces of a puzzle
• Task is to assemble pieces into a whole

• Taps knowledge of part-whole relationships,
  visual-motor coordination, anticipation of
  relationships among parts
• Fluid intelligence

41
Object Assembly

• Sensitive to cerebral damage, especially in R Hem
• Sensitive to disorder called neglect

• g correlation r .62

42
Scales and Norms for the WAIS

• Determine raw score for each subtest.
• Convert raw scores to standard scores, called
  scaled scores (M10, SD3)
• Convery to standard scores using tables for age
  (13 age groups).
• Subtest scaled scores are added, then converted
  to WAIS-III composite scores.
• Three composite scores Verbal, Performance,
  Full Scale, each with M100, SD15

43
Standardization of the WAIS

• Standardized on a stratified sample of 2,450
  adults representative of the US population aged
  16-89.
• There were 200 cases per age group, except for
  the smaller numbers in the two oldest groups.
• Still difficult to know the effects of
  self-selection since participants had to be
  invited and accept to be included.

44
Reliability of the WAIS

• Internal consistency and test-retest
  reliabilities .95 or higher for full scale and
  verbal scores.

• About .90 for performance and these index scores
  perceptual organization, working memory, and
  processing speed.

45
Reliability of the WAIS

• Internal consistency reliability for the subtests
  range from upper .70s to low .90s. Test-retest
  is about .83.

• Generally, performance reliabilities are lower
  than verbal reliabilities on the subtests.
• Why might that be?

46
Validity of the WAIS

• We have a great deal of information on
  criterion-related and construct validity.
• Factors analyses support use of 4 index scores.
• Most widely used ability test today

47
Johnson et al. (2004)

• Measured correlation between WAIS scores and two
  other test batteries
• Comprehensive Ability Battery (CAB)
• Hawaii Battery Ravens
• These batteries varied in their subtests, but
  correlations were essentially perfect

48
Comprehensive Abilities Battery

• 1. Numerical Ability Computations including
  fractions, decimal divisions, square roots, etc.
• 2. Spatial Ability Interpretation of
  two-dimensional figural rotation or reversal.
• 3. Memory Span Recall of digits presented
  aurally.
• 4. Flexibility of Closure Identification of
  embedded figures.
• 5. Mechanical Ability Identification of
  mechanical principles and tools.
• 6. Speed of Closure Completion of gestalt.
• 7. Perceptual Speed Evaluation of symbol pairs.
• 8. Word Fluency Production of anagrams.
• 9. Inductive Reasoning Identification of pattern
  in sequences of letter sets.
• 10. Associative Memory Rote memorization of
  meaningless pairings.
• 11. Meaningful Memory Rote memorization of
  meaningful pairings.
• 12. VerbalVocabulary Multiple choice among
  possible synonyms.
• 13. VerbalProverbs Interpretation of proverbs.
• 14. Spelling Multiple-choice identification of
  misspellings.

49
Hawaii Battery Ravens

• 15. Card Rotations Matching of rotated
  alternatives to probe.
• 16. Mental Rotation Identification of rotated
  versions of 2-D pre-presentation of 3-D objects.
• 17. Paper Form Board Outline of cutting
  instructions to form the target figure.
• 18. Hidden Patterns Identification of probe
  figures in more complex patterns.
• 19. Cubes Identification of matched figures
  after rotation.
• 20. Paper Folding Identification of unfolded
  version of a folded probe.
• 21. Raven Identification of analogous figure to
  follow a sequence of figures.
• 22. Vocabulary Multiple choice among possible
  meanings.
• 23. Subtractn/Multn Completion of two-digit
  subtractions and two-digit by one-digit
  multiplications.
• 24. Word Beg/Endings Generation of words
  beginning and ending with specified letters.
• 25. Pedigrees Identification of familial
  relationships within a family tree.
• 26. Things Categories Generation of things that
  share assigned characteristics.
• 27. Different Uses Generation of novel uses for
  specified objects.
• 28. Immed Vis Mem Recall of illustrations of
  common objects immediately following
  presentation.
• 29. Delay Visl Mem Recall of illustrations of
  same common objects after delay.
• 30. Lines and Dots Trace a path through a grid
  of dots.
• 31. Identical Pictures Identification of
  alternative identical to probe.

50
Johnson et al. (2004)

• Correlations
• WAIS Hawaii Battery Ravens 1.00
• WAIS Comprehensive Ability Battery 0.99
• Hawaii CAB 0.99
• These results constitute strong evidence for g
  and show that the one-factor result does not
  depend upon particular tasks

51
WISC-III

• Most popular test for assessing intellectual
  ability of children ages 6 years, 0 months to 16
  years, 11 months.
• Similar to structure of the WAIS, with easier
  items
• Both tests yield verbal, performance, and full
  scale IQ and 4 index scores
• Most of the subtests are the same

52
Psychometric Properties of the WISC-III

• Standardization program involved 2,200 cases
  selected to represent the US population of
  children aged 6-16.
• Composite scores generally have internal
  consistency reliabilities in the mid-.90s and
  test-retest reliabilities around .90.
• Subtest reliabilities are generally in the
  mid-.80s.
• Object Assembly and Mazes are problematic, with
  reliabilities in the .60s.