Outline David Wechsler – some history Wechsler’s Scales IQ scores Index scores Verbal subtests...

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Outline • David Wechsler – some history • Wechsler’s Scales • IQ scores • Index scores • Verbal subtests • Performance subtests • WAIS Psychometrics

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Transcript of Outline David Wechsler – some history Wechsler’s Scales IQ scores Index scores Verbal subtests...

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  • Outline David Wechsler some history Wechslers Scales IQ scores Index scores Verbal subtests Performance subtests WAIS Psychometrics
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  • 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
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  • 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
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  • 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 2 -7 1981: WAIS-R (revised form of 1955 test) 1997: WAIS-III
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  • 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
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  • 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
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  • Full Scale IQ Verbal IQPerformance IQ VCIWMIPOIPSI Vocabulary Similarities Information Comprehension Digit Span Arithmetic Letter-Number Sequencing Block Design Matrix reasoning Picture completion Picture arrangement Digit-Symbol Coding Symbol Search
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  • 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?
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  • Wechsler test produced 3 IQ scores Verbal IQ: Responses require person being tested to use language to understand instructions or to make a response
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  • Wechsler test produced 3 IQ scores Performance IQ: Performance subtests involve doing something, not just answering questions
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  • 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
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  • 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,
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  • 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
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  • Index scores Perceptual organization Use visual, spatial, and visually-guided motor skills Organize thoughts Assesses comfort with new, unfamiliar situations
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  • 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
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  • WAIS Verbal Tests Vocabulary Similarities Arithmetic Digit Span Information Comprehension Letter-Number Sequencing
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  • 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
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  • 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
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  • 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?
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  • Similarities Logical, abstract thinking Concept formation Crystallized and fluid intelligence With Information subtest, the second best for measuring g Correlation with g =.79
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  • 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
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  • Arithmetic Assesses working memory, numerical reasoning, computation skill, concentration, retrieval from LTM Influenced by emotional state Correlation with g is r =.75
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  • 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
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  • Digit Span Average 6.4 digits forward, 4.7 backwards DSF DSB 5 suggests brain damage Correlation with g: r=.57 (the worst)
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  • 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
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  • 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
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  • 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
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  • 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
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  • WAIS Performance Tests Picture completion Digit symbol-coding Block design Matrix reasoning Picture arrangement Symbol search (optional) Object assembly (optional)
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  • 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
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  • Digit Symbol Coding 1 X 2 39 8 9 1 6 3
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  • Visual STM Psychomotor speed Visual-motor coordination Visual sequencing Accuracy & speed g: correlation r =.59 Very sensitive to any kind of brain damage
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  • 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
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  • 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 ?
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  • Matrix reasoning Measures abstract thinking, nonverbal reasoning, analogy skill Fluid intelligence Visual organization g: correlation r =.72
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  • 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
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  • Picture Arrangement Failure may be due to visual problems (compare with Picture Completion) g: correlation r =.66
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  • 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?
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  • Symbol Search Visual-motor coordination and speed, planning, STM, perceptual speed Large practice effects in young adults g: correlation r =.70
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  • 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
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  • Object Assembly Sensitive to cerebral damage, especially in R Hem Sensitive to disorder called neglect g: correlation r =.62
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  • 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
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  • 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.
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  • 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.
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  • 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?
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  • 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
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  • 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
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  • Comprehensive Abilities Battery 1. Numerical Ability Computations including fractions, decimal divisions, square roots, etc. 2. Spatial AbilityInterpretation 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.
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  • Hawaii Battery + Ravens 15. Card RotationsMatching 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/MultnCompletion 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 MemRecall 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.
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  • Johnson et al. (2004) Correlations: WAIS Hawaii Battery + Ravens1.00 WAIS Comprehensive Ability Battery0.99 Hawaii CAB0.99 These results constitute strong evidence for g and show that the one-factor result does not depend upon particular tasks
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  • 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
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  • 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.