Ch 10

Background of the Wechsler Intelligence Scales

  • First Emergence: The Wechsler Intelligence Scales first emerged in 1939, shortly after the revision of the Binet scale.

  • Key Model: The Wechsler–Bellevue Intelligence Scale was introduced as a new model for assessing intelligence that moved away from a single score indication.

  • Focus on Nonintellective Factors: The model considered the role of "nonintellective" factors, which was a significant departure from previous models like the Binet scale.

  • Challenge to Previous Models: This scale questioned the inappropriateness of the Binet scale for use with adults, recognizing a need for a more nuanced approach to intelligence testing.

The Point Scale Concept

  • The Binet scale organized items strictly by age level, resulting in a methodology where no credit was received for items unless a minimum threshold was reached.

  • In contrast, the point scale awards credit (points) for each item, facilitating the grouping of similar items together. This feature was subsequently adopted in later revisions of the Binet scale.

  • Advantages of the Point Scale: This approach allows consideration of various skill areas, enhancing the precision and applicability of intelligence testing.

The Performance Scale Concept

  • The Wechsler scales examined nonverbal intelligence in a more comprehensive way than early Binet scales.

  • It focused on skills beyond childhood years, recognizing that cognitive abilities evolve.

  • Original Structure: The original Wechsler test had two main scales: the verbal and performance scales, which reduced bias potentially arising from language and culture.

Evolution of the Wechsler Intelligence Scales

  • Historical Progression:

    • Wechsler–Bellevue Intelligence Scale (WBIS) - 1939

    • Wechsler Adult Intelligence Scale (WAIS) - 1955

    • WAIS-R - 1981

    • WAIS-III - 1997

    • WAIS-IV - 2008

    • WAIS-V - 2024

Scales, Subtests, and Indexes

Subtests and Major Functions

  • Vocabulary: Measures vocabulary level.

  • Similarities: Assesses abstract thinking.

  • Arithmetic: Tests concentration through problem-solving.

  • Digit Span: Measures immediate memory and anxiety.

  • Information: Evaluates range of knowledge.

  • Coding: Assesses visual–motor functioning.

  • Block Design: Tests nonverbal reasoning and spatial visualization.

  • Matrix Reasoning: Assesses inductive reasoning.

  • Visual Puzzles: Tests perceptual reasoning.

  • Symbol Search: Measures information-processing speed.

Indexes and Their Components

  • Verbal Comprehension Index (VCI) & Components:

    • Vocabulary, Similarities, Information, and Comprehension.

    • Detail on Vocabulary: Measures not only vocabulary ability (word knowledge) but also includes aspects like speech fluency and word-finding. Example: "What does 'evoke' mean?"

    • Detail on Similarities: Assesses verbal abstract reasoning by presenting words two at a time for comparison, e.g., "In what way are a pencil and a paintbrush alike?"

    • Detail on Information: Measures general knowledge. Example: "On what continent is the Nile river?"

  • Working Memory Index (WMI) & Components:

    • Digit Span, Arithmetic, and Letter-Number Sequencing.

    • Detail on Digit Span: Involves verbal attention and working memory. Example: Repeat a sequence: "9-5-4-7-2."

    • Detail on Arithmetic: Assesses mental arithmetic and working memory with problems posed verbatim. Example: "If Sophia runs for twenty minutes each day from Monday through Friday and thirty minutes on Saturday and Sunday, how many minutes does she run in a week?"

    • Detail on Letter-Number Sequencing: Individual reorders lists of numbers and letters. Example: Convert Z-3-B-1-2-A to 1-2-3-A-B-Z.

  • Perceptual Organization Index (POI) & Components:

    • Block Design and Matrix Reasoning.

    • Detail on Block Design: Tests visuomotor construction and organization by having examinees match visual stimuli using blocks.

    • Detail on Matrix Reasoning: Involves visual abstract reasoning, forcing the examinee to identify which response completes a visual pattern.

  • Processing Speed Index (PSI) & Components:

    • Digit Symbol-Coding and Symbol Search.

    • Detail on Digit-Symbol Coding: Measures psychomotor speed where symbols must be drawn in response to numbered boxes, linking a number with a symbol.

    • Detail on Symbol Search: Assesses processing speed and visual search. The examinee identifies and crosses out target items quickly.

Score Transformations

  • Composite index scores are determined by summing scaled scores, where raw scores are transformed into scaled scores with a mean of 10 and a standard deviation of 3.

  • Normative Comparison: Scaled scores use 13 normative age groups to create a standardized measurement.

  • Demographic T Scores: (DemTs) can be calculated to adjust for age, ethnicity, and gender, enhancing the interpretive power of test results.

Index Scores

  • Verbal Comprehension: A refined measure surpassing the traditional verbal IQ score, indicating crystallized intelligence.

  • Perceptual Organization: Indicative of fluid intelligence.

  • Working Memory: Represents a significant advancement in the evolution of IQ testing.

  • Processing Speed: Evaluates how rapidly cognitive processes occur.

Full-Scale IQ (FSIQ)

  • The FSIQ is computed by summing the age-corrected scaled scores of the four index composites:

    • Mean: 100

    • Standard Deviation: 15

Interpretive Features of the Wechsler Tests

Index Comparisons

  • Nonverbal measures can aid in interpreting verbal scores, especially where deficits are present.

  • Discrepancies between Verbal IQ (VIQ), Performance IQ (PIQ), and FSIQ can highlight specific cognitive challenges rather than a generalized intellectual deficit.

Pattern Analysis

  • Significant differences between subtest scaled scores may provide insight into various emotional difficulties.

  • Research into the validity of these discrepancies is inconsistent, leading to recommendations that such analyses be used for hypothesis generation rather than conclusive diagnostic purposes.

Psychometric Properties of the Wechsler Adult Scale

  • Involves a sample size of 2200 adults, categorized across 13 age groups and 13 specialty groups.

  • Standardization: The Wechsler scales exhibit high reliability, assessed in both internal and temporal contexts.

  • Validity: It is regarded as one of the most valid measures for testing IQ globally.

Evaluation of the Wechsler Adult Scale

  • The reliability of the four index scores and the FSIQ is well established, yet the validity of certain interpretations generated from the Wechsler tests has moments of critique, suggesting results are sometimes used inappropriately.

Downward Extensions of the WAIS-IV: The WISC-V and the WPPSI-IV

WISC-V: Wechsler Intelligence Scale for Children

  • Appropriate for ages 6 to 16 years.

  • History: Initially developed in 1949, with revisions in 1974, 1991, 2003, and 2014, leading to its current fifth edition (WISC-V).

WPPSI-IV: Wechsler Preschool and Primary Scale of Intelligence

  • Suitable for ages 2.5 years to 7 years and 7 months.

  • Developed initially in 1967 with revisions in 1989, 2003, and 2012, leading to its current fourth edition (WPPSI-IV).

Improvements in WISC-V

  • Represents significant advancements in terms of standardization, reliability, and validity, continuing the model established by WAIS-IV.

  • Retains methods of pattern analysis and index score comparisons, though such methods remain under scrutiny.

Improvements in WPPSI-IV

  • Expanded age testability and incorporates flexibility based on individual testee specifics.

  • Maintains a similar hierarchical structure to WISC-V and aligns well with measures of adaptive functioning for diagnostic uses, supported by robust psychometric properties.