Weiss L. G. et al. (2009): WAIS-IV Clinical Use and Interpretation

Chapter 1: WAIS-IV: Advances in the Assessment of Intelligence

 Wechsler’s theory of intelligence
The historical background: Galton and Cattell had started attempts to measure intelligence. Spearman and Thorndike discussed their different views on the structure and definition of intelligence. Advances in psychometrics, especially factor an
alysis, had an impact on development and evaluation of intelligence measures.

Two primary theories of intelligence (before Wechsler):

    • Spearman: The ”g” factor, a general factor of intelligence reflecting overall intelligence. Later specific factors (reflecting specialized abilities, that share some variance with the overall intelligence) were included in the theory.
    • Thorndike: No general intelligence factor, but different kinds of intelligence, ex abstract, social, practical intelligences.

Wechsler’s definition of intelligence: Includes aspects of both Spearman and Thorndike. Wechlser believed in a general (global) intelligence, which is composed of qualitatively different abilities, incl. cognitive abilities and other non-intellective abilitie
s like drive, persistence, temperament, curiosity.

Revisions of WAIS: Scale revisions have been based on psychometric and theoretical advances, clinical research and practical needs, not changes in Wechsler’s definition of intelligence.

STRUCTURE AND CONTENT OF THE WAIS-IV
   15 subtests, 4 index scalesWAIS item oversigt(12 subtests for people over 69 years of age)
 Verbal Comprehension
(4 subtests)

 

 Similarities: An individual describes how two words or concepts are similar.

What does it measure? Verbal concept formation, abstract reasoning, categorical thinking, ability to distinguish between non-essential and essential features.

Vocabulary: Composed of verbal items. The individual defines words, which are presented and read aloud by the examiner. (To extend the floor of the subtest, picture items, which are to be named by the examinee, are also available.)

What does it measure? Verbal concept formation, language development, word knowledge, requires long-term memory.

Information: Questions addressing a broad range of general knowledge.

What does it measure? Fund of knowledge, long-term memory and retrieval, verbal comprehension, crystallized intelligence.

Comprehension: Questions based on an understanding of basic principles and social situations (not factual knowledge), ex ”Why must cars have license plates?”.

What does it measure? Verbal conceptualization, verbal expression, practical knowledge, social judgment, crystallized intelligence, common sense.

 Perceptual Reasoning
(5 subtests)

 

 Block Design: The task is to reproduce pictured designs using specially designed red/white coloured blocks. The task is timed.

What does it measure? Non-verbal reasoning, analysis and synthesis, visual perception and organization, visual-motor coordination.

Matrix Reasoning: The task is to complete a matrix or serial reasoning problem by selecting the missing section from 5 response choices. Not timed.

What does it measure? Fluid intelligence, visuospatial ability, simultaneous processing, perceptual organization.

Visual Puzzles: The individual has to select 3 response options (from 6) that could be combined to reproduce a geometric image. (Replaces the ”Object Assembly” task from WAIS III). Items are timed.

What does it measure? Perceptual reasoning, visuospatial ability, analysis and synthesis, simultaneous processing.

Figure Weights: The individual has to select the option (out of 5 possible) that would keep a pictured scale in balance. Timed.

What does it measure? Fluid reasoning, quantitative and analogical reasoning.

Picture Completion: Consists of a pictured object or scene with a missing part. The individual must identify the missing part within 20 sec.

What does it measure? Visual perception, perceptual organization, attention to visual detail.

 Working Memory (3 subtests)  Digit Span: Includes 3 tasks. Forward, where the individual repeats numbers spoken by the examiner. Backward, where the individual repeats numbers in reverse order. Sequencing, where the individual has to sequence spoken numbers from lowest to highest. No time limit.

What does it measure? Working memory, attention, auditory processing, mental manipulation.

Arithmetic: The individual has to mentally solve arithmetical word problems within a time limit.

What does it measure? Working memory, mental manipulation, attention, concentration, sequential processing, numerical reasoning.

Letter-Number Sequencing: The examiner reads out a series of letters and numbers and the individual has to recall first the numbers (in ascending order), then the letters (in alphabetical order). No time limit.

What does it measure? Working memory, mental manipulation, attention, concentration, short-term auditory memory.

 Processing Speed

(3 subtests)

 

 Symbol Search: The individual has to search for 2 symbols within a row of symbols and mark either the matching symbol or a ”no” box if the symbol is not present. Within 120 sec. the individual has to complete as many rows as possible.

What does it measure? Visuomotor processing speed, short-term visual memory, visual discrimination, attention, concentration.

Coding: The individual must copy as many simple symbols as possible within 120 sec. The code is based on a key that pairs numbers with the symbols.

What does it measure? Visuomotor processing speed, short-term visual memory, learning ability, cognitive flexibility, attention, concentration, motivation.

Cancellation: The individial must search for specific coloured shapes within a larger array of coloured shapes, marking only the specified shapes. Time limit 45 sec.

What does it measure? Visuomotor processing speed, visual selective attention, visual neglect.

 Score descriptions Primary scores:

  • Subtest score, can be scaled to a metric with a mean of 10 and a SD of 3.
  • Index score, represents the sum of scaled scores for the subtests within a domain, ex working memory index. Can be scaled to a metric with a mean of 100 and a SD of 15.
  • Full Scale score,  can also be scaled to a metric with a mean of 100 and a SD of 15.

Optional scores:

  • On subtest-level: designed to produce additional information on a person’s performance on specific subtests. Available for Block Design and Digit Span.
  • On index-level: the General Ability Index. Derived from the sum of scaled scores for the main Verbal Compr. and Percept. Reas. subtests. Provides a score which is less influenced by the demands of working memory and processing speed.
WAIS-III to WAIS-IV:

What’s new?

Changes to structure and content:

  • Most notable change = Index scores have become the primary level of clinical interpretation, compared to Verbal IQ and Performance IQ in WAIS-III.
  • The Wechsler theoretical model now includes: verbal conceptualization, perceptual reasoning, working memory and processing speed.
  • The contribution of the PSI (Processing Speed) to the FSIQ has more than doubled in WAIS-IV (20 %) compared to WAIS-III (9 %).
  • The new edition shows increased emphasis on Processing Speed and Working Memory.
  • New subtests: Visual Puzzles (instead of Picture Completion), Cancellation, Figure Weights.
  • Eliminated subtests: Object Assembly, Picture Arrangement, and parts of other subtests. Other items were renewed, ex Arithmetics.

Other changes:

  • WAIS-IV instructions emphasize teaching, with all examinees receiving instruction regarding demands of the subtest task.
  • Reduced testing time from 80 min. to 67 min. partly due to reduction of number of subtests. Should result in reduced fatigue, and provide time for evaluating other aspects of cognitive functioning, ex adaptive behaviour, memory and executive function.
Future research and revisions Revisions of the test represent advances in related fields such as neuropsychology, cognitive psychology, cognitive neuroscience, intelligence theory, psychometrics etc.

Possible areas for future research incl. functional brain imaging with evidence suggesting localized brain activation for specific cognitive abilities and more diffuse activation for general intellectual ability.

Chapter 3: Theoretical, Empirical and Clinical Foundations of the WAIS-IV Index Scores

 The Wechsler model With the revision of WAIS (from III à IV) the Wechsler model of intelligence has shifted from a two-part structure comprising the Verbal IQ and the Performance IQ à a four factor-based structure comprising the four indexes: Verbal Conceptualisation, Perceptual Reasoning, Working Memory and Processing Speed.

Due to theoretical developments, empirical findings and greater understanding of concepts in fields like neurocognition, a greater differentiation between neurocognitive processes related to intelligence has been made possible. Ex subtests related to working memory and perceptual reasoning have been singled out from VIQ and PIQ as two separate areas of importance.

Fluid reasoning

or intelligence

Fluid intelligence or fluid reasoning is the capacity to think logically and solve problems in novel situations, independent of acquired knowledge. It is the ability to analyze novel problems, identify patterns and relationships that underpin these problems and the extrapolation of these using logic.
Crystallized intelligence

 

Crystallized intelligence is the ability to use skills, knowledge, and experience. It should not be equated with memory or knowledge, but it does rely on accessing information from long-term memory.

Crystallized Intelligence is one’s lifetime or intellectual achievement, as shown largely through one’s vocabulary and knowledge of world affairs.

THE WAIS-IV INDEX SCORES
Verbal Comprehension Index  (Vocabulary, Information, Similarities, Comprehension)

Reflects an individuals ability to comprehend verbal stimuli, reason with semantic material and communicate thoughts and ideas with words.

Crystallized knowledge is the background within which these abilities are assessed. Depends partly on a person’s educational and general life experience, but also on the person’s ability to comprehend acquired knowledge and apply it appropriately.

The Vocabulary subtest is one of the highest ”g” loaded subtests and one of the best predictors of overall intelligence.

Perceptual Reasoning Index  (Block Design, Matrix Reasoning, Visual Puzzles, Figure Weights, Picture Completion)

Measures fluid reasoning with some perceptual organization, as fluid reasoning cannot be measured separately, but requires an object.

Quantitative and analogical reasoning (FW), non-verbal fluid reasoning and the ability to maintain a visual image in mind temporarily while mentally manipulating it (VP)…

Working Memory Index

 

 (Digit Span, Arithmetic, Letter-Number Sequencing)

Measures attention, concentration and working memory (the ability/mental control to hold information in mind temporarily, while performing some operation or manipulation on that information).

Ex Baddeleys seminal model of the working memory system. This consists of a phonological loop, a visual-spatial sketchpad (stores and refreshes verbal and visual stimuli), a central executive (controls attention) and an episodic buffer.

Variations in scores on the different subtests (ex average on DS and LN and low scores on AR) may not indicate a deficit in working memory, but rather a lack of having learnt the arithmetic skills needed or a specific learning difficulty related to maths and arithmetic.

Processing Speed Index

 

(Coding, Symbol Search, Cancellation)

Measures the speed of mental processing, using visual and graphomotor skills, and is related to the efficient use of other cognitive skills.

The PSI indicates the rapidity with which a patient processes simple or routine information without making errors. PS interacts in a critical way with other higher-order cognitive functions and may impact general cognitive functions, new learning, reasoning, and everyday performances.

There are large and obvious age-related trends in processing speed. Ex it has been argued that the decline observed in general mental ability with age, is mainly due to a slowing of mental processing speed.

 Executive Functions Organisation, planning and other executive functions can impact performance on various WAIS-IV subtests.

Executive functions is an umbrella term including much more than just organisation and planning, ex working memory, decision-making, cognitive flexibility etc. Can be defined as the effective integration of multiple cognitive processes relevant to goal-directed behaviour.

In the real world executive functions are also essential for the expression of intelligent behaviour in work and life. Ex even for a very bright person, poor planning and disorganisation can interfere with the obtainment of specific goals.

But what is the relationship between intelligence and executive functions? Are executive functions really something different and apart from fluid reasoning?

 Diagnosis

 

WAIS-IV is not intended to be diagnostic of ex AD/HD or any other complex disorder, but should rather be used as another ”indicator” supporting or not, the eventual diagnosis of any condition in which cognition is implicated.

WAIS-IV scores can and should not be used as diagnostic markers.

Toward a dynamic model of intellectual abilities Increasing evidence supports the role of processing speed and working memory in intelligence.

Studies suggest that as children develop normally, more rapid processing of information results in more effective use of working memory space, which enhances performance on many reasoning tasks.

The interrelatedness between working memory, reasoning, prior knowledge and processing speed has led researchers to question whether reasoning ability is more than working memory capacity.

When analyzing a subtest it is important to remember the interrelatedness of complex cognitive abilities.

Analyzing differences among index scores

 

A general rule of thumb: 12 or more point differences are likely to be clinically meaningful for all comparisons except PSI, which may require 14 point differences.

(Appendix B shows the critical differences necessary to obtain statistically significant differences with any pair of index scores.)

 THE WAIS-IV COMPOSITE SCORES
  • General Ability Index (GAI)

 

Summarizes performance on the VCI and PRI into a single score.

These two indexes represent the most highly ”g” loaded subtests.

First developed to be used in ability-achievement discrepancy analyses (because many learning-disabled students exhibit deficits in working memory and processing speed tasks, resulting in a lower FSIQ). The GAI therefore gives a better estimate of cognitive ability.

May be useful to estimate overall ability when physical or sensory disorders invalidate performance on WM and/or PS tasks.

However, as WM and PS are supposed to be important components in a comprehensive assessment of intelligence, they are only to be omitted if there are sound reasons for doing this (ex sensory or physical impairments, disturbance of testing session, invalid administration due to lack of effort etc.), not just because an individual performs poorly on the two areas.

 

  • Cognitive Proficiency Index (CPI)

 


Summarizes performance on WMI and PSI into a single score.

The CPI represents proficient processing through quich visual speed and good mental control, which facilitates fluid reasoning and learning of new material.

GAI and CPI can provide different views into the patient’s cognitive abilities when there is significant variability across relevant index scores.

As a rule of thumb, 15 point differences or more indicate statistical significance.

Estimating overall ability The FSIQ has strong explanatory power, but may mask individual differences among the four indexes.

 

Skriv et svar

Udfyld dine oplysninger nedenfor eller klik på et ikon for at logge ind:

WordPress.com Logo

Du kommenterer med din WordPress.com konto. Log Out / Skift )

Twitter picture

Du kommenterer med din Twitter konto. Log Out / Skift )

Facebook photo

Du kommenterer med din Facebook konto. Log Out / Skift )

Google+ photo

Du kommenterer med din Google+ konto. Log Out / Skift )

Connecting to %s