Transcript The Wechsler Intelligence Scales

The Wechsler
Intelligence Scales
The Wechsler Adult Intelligence
Scale (WAIS)
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The first Wechsler intelligence scale, known as
the Wechsler-Bellevue Intelligence Scale, was
developed in 1939, two years after the 1937
version of the Stanford-Binet
Developed in reaction to problems with the 1937
Stanford-Binet
• SB items had been selected for use with children, &
weren’t really appropriate for adults
• SB had lots of timed tests, which made it difficult for
older adults
• SB did not consider that intellectual performance can
deteriorate as a person grew older
• SB produced only 1 score
Point & Performance Scale
Concepts
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point scale concept
• with earlier SB tests, there were a number of
different kinds of tasks & items at different age
levels; more verbal at older ages
• in Wechsler scales, all items of a particular
type are grouped together, and are presented
in order of increasing difficulty
• points are assigned to each item, allowing for
a calculation of a score for each type of task,
or for each content area
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Performance Scale Concept
• earlier forms of SB largely dependent on verbal
ability, especially in the test for the older age
ranges
• Wechsler scales include measures of
PERFORMANCE (reflecting non-verbal abilities),
as well as scales reflecting VERBAL abilities
• comparison of verbal & performance scores
provides a great deal of information, for
example, in identifying children with learning
disabilities
• performance scale is less affected by language
and cultural factors
The Wechsler Adult Intelligence
Scale III (WAISIII)
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Most recent version of the adult intelligence scale
(there are also child & pre-school versions)
Published in 1997
developed for use with individuals aged 16
through 89
takes 60 to 90 minutes to administer
Wechsler believed in a single factor of
intelligence, but thought that it consisted of
specific, interrelated elements
to get a measure of overall intelligence, simply
aggregate the capabilities on each of the
separate elements
Subtests of WAISIII
Verbal Subtest
Major Function Measured
Vocabulary
Vocabulary level
Similarities
Abstract thinking
Arithmetic
Concentration
Digit span
Information
Immediate memory,
anxiety
Range of knowledge
Comprehension
Judgment
Letter-number
sequencing*
Freedom from
distractibility
Performance Subtest Major Function
Measured
Picture completion
Alertness to details
Digit symbol-coding
Visual-motor functioning
Block design
Nonverbal reasoning
Matrix reasoning
Inductive reasoning
Picture arrangement
Planning ability
Symbol search*
Information-processing
speed
Analysis of part-whole
relationships
Object assembly*
Scoring
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each subtest produces a raw score – i.e., a total
number of points – and has a different maximum
total – e.g., vocabulary has 33 items, scored 0, 1
or 2 for a maximum of 66 points
raw score for each subtest (total no. of points) is
converted to a scaled score with a mean of 10
and a standard deviation of 3
there are separate norms for ages 16-17; 18-19;
20-24; 25-29; 30-34; 35-44; 45-54; 55-64; 6569; 70-74; 75-79; 80-84; 85-89
Scaled score equivalents of raw scores:
20 to 24 year old norms
Verbal IQ Score
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to obtain a verbal IQ score, 6 of the
7 verbal scaled scores are summed
(letter-number sequencing is not
included)
then a table formed from a
standardization sample of individuals
from all groups used to get verbal IQ
resultant IQ is a deviation IQ with a
mean of 100 and s.d. of 15
Performance IQ Score
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to obtain a performance IQ score, 5 of the
7 performance scaled scores are summed
(symbol search & object assembly not
included)
then a table formed from a
standardization sample of individuals from
all groups used to get performance IQ
resultant IQ is a deviation IQ with a mean
of 100 and s.d. of 15
Full-Scale IQ Score
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to obtain full-scale IQ, sum scaled
scores of 11 verbal and performance
non-optional subtests, and use table
based on standardization sample
Index Scores
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in addition to grouping tests into verbal
and performance categories, can group
them into four different skill areas:
• verbal comprehension [crystallized
intelligence]
• perceptual organization [fluid intelligence]
• working memory
• processing speed [how quickly mind works]
Structure of the Scale
FSIQ
VIQ
VCI
Vocabulary
Similarities
Information
Comprehension
PIQ
WMI
Digit Span
Arithmetic
Letter–Number
Sequencing
POI
PSI
Block Design
Matrix Reasoning
Picture Completion
Picture Arrangement
Digit Symbol—
Coding
Symbol Search
8
Plotting Subtest Scores (IQ)
15
Reliability
Split-Half
Test-Retest
Full Scale
.98
.95
Verbal IQ
.97
.94
Performance IQ
.94
.88
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For full-scale IQ, standard error of measurement
is quite small, around 2 to 2.5 IQ points
This means that an examinee’s true score will fall
within 5 points either side of the obtained score
95% of the time
Reliability of Subtests
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Reliabilities for the subtests vary a
great deal, and are lower than
reliabilities of the full-scale, verbal,
performance IQ’s, and the four
indexes
They range from low .70’s to low
.80’s, with some in the .60’s
Validity of the WAIS
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WAISIII correlates highly (mid 90’s) with earlier
versions of the WAIS
Correlation with SBIV is .88
Correlates significantly with grades in high school,
university
IQ and occupational attainment are also
significantly correlated
Predictions deriving from theory are borne out; fluid
intelligence supposedly declines more rapidly in old
age than crystallized intelligence
• Supported by finding that verbal subtests show minimal
decrement with age, while performance subtests drop
markedly
Conry & Plant (1965)
Interpreting the WAIS
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Verbal-Performance IQ Comparisons
• Neurological impairment may be indicated
when one of the scales falls in the low average
or lower range, and the other in the average or
higher range
• Emotional trauma may be indicated if the
client has a low verbal or performance IQ that
does not seem to match their past level of
functioning
• Language-related learning difficulty may
be indicated by an low verbal IQ and average
or high performance IQ
Case Study: Stephen Gould
High Stakes?
Atkins vs. the State of
Virginia
The Wechsler Intelligence Scale for
Children (WISC)
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First published in 1949
Revised in 1974, 1991
Current version is WISC-IV,
published in 2003
WISC-IV
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Measures intelligence from ages 6
through 16
Contains 15 subtests
Abandons VIQ-PIQ
Instead produces four major indices:
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Verbal comprehension
Perceptual reasoning
Processing speed
Working memory
Wechsler (1958)
“[The grouping of subtests into Verbal and
Performance areas]…does not imply that these
are the only abilities involved in the tests…The
subtests are different measures of intelligence,
not measures of different kinds of intelligence,
and the dichotomy of Verbal and Performance
areas is only one of several ways in which the
tests could be grouped.”
In: The measurement and appraisal of adult intelligence. (pg 64)
The structure of the WISC-IV
The WISC-IV has four specific cognitive domains (Indexes) which
together contribute to the Full Scale IQ
FULL Scale IQ
Verbal
Comprehension
Perceptual
Reasoning
Working
Memory
Processing
Speed
© Text, format, graphics and data Copyright Dr John Worthington all rights reserved 2004 ©
www.jweducation.com
The structure of the WISC-IV
Each of the four Index scores is derived from a number of subtest scores.
There are five supplemental subtests which can be substituted for a specified
number of core subtests if needed.
WISC-IV Full Scale IQ
Verbal Comprehension
Index
Perceptual Reasoning
Index
SI
BD
VC
CO
PCn
MR
Working Memory
Index
DS
LN
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www.jweducation.com
Processing Speed
Index
CD
SS
Verbal Comprehension Subtests
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SIMILARITIES (SI)
Individuals are presented with two words that represent common
objects or concepts and asked to say how they are similar.
VOCABULARY (VC)
Younger individuals are shown pictures and asked to name them.
Then individuals are asked to give definitions for words presented
orally and visually.
COMPREHENSION (CO)
Individuals are asked to respond to questions requiring an
understanding of social situations, reflecting common sense,
social judgment, behaviour and conventional standards.
INFORMATION (IN) (Supplemental subtest)
Individuals answer questions that address a broad range of
general knowledge topics.
WORD REASONING (WR) (Supplemental subtest)
Individuals are asked to identify the common concept
described in a series of clues.
© Text, format, graphics and data Copyright Dr John Worthington all rights reserved 2004 ©
www.jweducation.com
Word Reasoning (supplemental)
Verbal Comprehension Index
“Let’s play a guessing game. Tell me what I’m thinking of.”
Let’s test the ceiling item…
This has never been seen or done before…
and it can make our lives better and easier…
and it is a product of the mind.
1 point: discovery, invention, innovation,
technology, imagination, creativity,
dream
Perceptual Reasoning Subtests
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BLOCK DESIGN (BD)
Individuals use up to nine red and white blocks to re-create a
model or a picture of a design within a specific time limit.
PICTURE CONCEPTS (PCn)
The individual is presented with two or three rows of pictures and
chooses one picture from each row with common characteristics.
MATRIX REASONING (MR)
Individuals look at an incomplete matrix (made up of pictures or
designs)
and selects the missing item from five options.
PICTURE COMPLETION (PCm) (Supplemental subtest)
Individuals have to point to or name an important part missing
from a picture within a specific time.
© Text, format, graphics and data Copyright Dr John Worthington all rights reserved 2004 ©
www.jweducation.com
Picture Concepts (core)
Perceptual Reasoning Index
“Pick one here..
“that goes with
one here..”
Sample items only: “Why do they go together?”
Matrix Reasoning
Working Memory Subtests
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DIGIT SPAN (DS)
Digit Span requires the individual to do two distinct tasks;
the first is to repeat orally presented numbers in the same
order. Then the individual is asked to repeat orally
presented numbers in reverse order.
LETTER-NUMBERING SEQUENCING (LN)
Individuals are read a sequence of numbers and letters and
are asked to recall the numbers in ascending order and the
letters in alphabetical order.
ARITHMETIC (AR) (Supplemental subtest)
Individuals solve a series of orally presented arithmetic
problems within a specific time limit.
© Text, format, graphics and data Copyright Dr John Worthington all rights reserved 2004 ©
www.jweducation.com
Letter-Number Sequencing
“Tell me the numbers first, in order, starting with
the lowest number. Then tell me the letters in
alphabetical order.”
Credit is given if produced “in order”
(i.e., correct sequence), even if letters are listed first.
Processing Speed Subtests
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CODING (CD)
Individuals copy symbols that are paired with simple
geometric shapes or numbers within a specific time limit.
SYMBOL SEARCH (SS)
Individuals scan a search group (of abstract symbols) and
indicate if a target symbol/s matches any of the symbols in
the search group within a specific time limit.
CANCELLATION (CA) (Supplemental subtest)
Individuals scan both a random and structured arrangement of
pictures and marks target pictures within a specific time limit.
© Text, format, graphics and data Copyright Dr John Worthington all rights reserved 2004 ©
www.jweducation.com
Cancellation (supplemental)
Processing Speed Index
“When I say go, draw a line through each animal. Work as
quickly as you can w/out making any mistakes. Tell me
when you are finished.”
Random vs Structured
Qualitative Descriptions
(same)
Score
Classification
130 and above
120–129
110–119
90–109
80–89
70–79
69 and below
Very Superior
Superior
High Average
Average
Low Average
Borderline
Extremely Low
Reliability of WISC-IV
Validity of WISC-IV
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Correlates .89 with WISC-III
Good at identifying:
• Children who are intellectually gifted
• Children with mild or moderate mental
retardation
• Children with reading, written
expression & math disorders
• Children with learning disabilities &
ADHD
Wechsler Preschool & Primary
Scale of Intelligence (WPPSI)
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Downward extension of WAIS &
WISC, originally for children from 4
to 6 years of age
First published in 1967
Latest version is WPPSI-III (2003),
for children from 2 years 6 months to
7 years 3 months
Similar to WISC-IV, though much
simpler
Psychometric Properties of WPPSI
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Reliabilities:
• For composite scales: .89 to .96
• subtests: .83 to .95
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Validity:
• Correlations with other tests of
intelligence for this age group range
from low (.49 with K-ABC) to moderate
(.74 to .90 with McCarthy, SB & other
scales)