Outline
•
•
•
•
•
•
•
David Wechsler – some history
Wechsler’s Scales
IQ scores
Index scores
Verbal subtests
Performance subtests
WAIS Psychometrics
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
David Wechsler
• Worked at NY’s 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
Binet’s emphasis on speed hurt older adults’ scores
Wechsler Scales
• 1939: the Wechsler-Bellevue, later called the WAIS.
• 1945: the Wechsler Memory Scale
• 1949: the children’s 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
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 person’s
intellectual ability
• aggregate: that one score is composed of a number of
sub-scores
Wechsler’s 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
Full Scale IQ
Verbal IQ
VCI
Vocabulary
Similarities
Information
Comprehension
Performance IQ
WMI
Digit Span
Arithmetic
Letter-Number
Sequencing
POI
Block Design
Matrix reasoning
Picture completion
Picture arrangement
PSI
Digit-Symbol
Coding
Symbol Search
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?
Wechsler test produced 3 IQ scores
• Verbal IQ:
• Responses require
person being tested to
use language – to
understand instructions
or to make a response
Wechsler test produced 3 IQ scores
• Performance IQ:
• Performance subtests
involve doing
something, not just
answering questions
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
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,
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
Index scores
• Perceptual organization
• Use visual, spatial, and
visually-guided motor
skills
• Organize thoughts
• Assesses comfort with
new, unfamiliar
situations
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
WAIS Verbal Tests
•
•
•
•
•
•
•
Vocabulary
Similarities
Arithmetic
Digit Span
Information
Comprehension
Letter-Number Sequencing
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
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
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?”
Similarities
• Logical, abstract
thinking
• Concept formation
• Crystallized and fluid
intelligence
• With Information
subtest, the second
best for measuring g
• Correlation with g =.79
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
Arithmetic
• Assesses working
• Correlation with g is r
memory, numerical
= .75
reasoning, computation
skill, concentration,
retrieval from LTM
• Influenced by emotional
state
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
Digit Span
• Average 6.4 digits
forward, 4.7 backwards
• DSF – DSB ≥ 5 suggests
brain damage
• Correlation with g:
r=.57 (the worst)
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
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
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
Letter-number sequencing
• Optional – not needed
to compute IQ
• Task is to re-order
intermixed, randomlysequenced 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
WAIS Performance Tests
•
•
•
•
•
•
•
Picture completion
Digit symbol-coding
Block design
Matrix reasoning
Picture arrangement
Symbol search (optional)
Object assembly (optional)
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
Digit Symbol Coding
1
2
3
X
╫
÷
9
1
6
…
9
…
3
8
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
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
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
Ō
ō
Ǒ
?
Matrix reasoning
• Measures abstract
thinking, nonverbal
reasoning, analogy skill
• Fluid intelligence
• Visual organization
• g: correlation r = .72
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
Picture Arrangement
• Failure may be due to
visual problems
(compare with Picture
Completion)
• g: correlation r = .66
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?
Symbol Search
• Visual-motor
• g: correlation r = .70
coordination and speed,
planning, STM,
perceptual speed
• Large practice effects in
young adults
Object Assembly
• Subject given pieces of
a puzzle
• Task is to assemble
pieces into a whole
• Taps knowledge of partwhole relationships,
visual-motor
coordination,
anticipation of
relationships among
parts
• Fluid intelligence
Object Assembly
• Sensitive to cerebral
damage, especially in R
Hem
• Sensitive to disorder
called neglect
• g: correlation r = .62
Scales and Norms for the WAIS
• Determine raw score for each subtest.
• Convert raw scores to standard scores, called
scaled scores (M=10, SD=3)
• 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 M=100, SD=15
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 selfselection since participants had to be
invited and accept to be included.
Reliability of the WAIS
• Internal consistency and • About .90 for
test-retest reliabilities
performance and these
.95 or higher for full
index scores:
scale and verbal scores.
perceptual organization,
working memory, and
processing speed.
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?
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
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
Comprehensive Abilities Battery
1. Numerical Ability
2. Spatial Ability
3. Memory Span
4. Flexibility of Closure
5. Mechanical Ability
6. Speed of Closure
7. Perceptual Speed
8. Word Fluency
9. Inductive Reasoning
10. Associative Memory
11. Meaningful Memory
12. Verbal—Vocabulary
13. Verbal—Proverbs
14. Spelling
Computations including fractions, decimal divisions,
square roots, etc.
Interpretation of two-dimensional figural rotation or
reversal.
Recall of digits presented aurally.
Identification of embedded figures.
Identification of mechanical principles and tools.
Completion of gestalt.
Evaluation of symbol pairs.
Production of anagrams.
Identification of pattern in sequences of letter sets.
Rote memorization of meaningless pairings.
Rote memorization of meaningful pairings.
Multiple choice among possible synonyms.
Interpretation of proverbs.
Multiple-choice identification of misspellings.
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.
Johnson et al. (2004)
•
•
•
•
Correlations:
WAIS – Hawaii Battery + Ravens
WAIS – Comprehensive Ability Battery
Hawaii – CAB
1.00
0.99
0.99
• These results constitute strong evidence for g and
show that the one-factor result does not depend
upon particular tasks
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
Psychometric Properties of the WISCIII
• 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 testretest reliabilities around .90.
• Subtest reliabilities are generally in the mid-.80s.
• Object Assembly and Mazes are problematic, with
reliabilities in the .60s.
Descargar

David Wechsler - Instructional Web Server