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Melissa Farrall's WISC-III  v. WISC-IV Comparison

Myth of the WISC-III/WISC-IV Retest: the Apples and Oranges Effect 

According to a study in which 244 children aged 6-16 were administered the WISC-IV and the WISC-III in counterbalanced order, the WISC-IV correlates well with the WISC-III.[1]  The table on page 65 indicates that those taking the WISC-IV would receive scores that are slightly lower than those earned on the WISC-III.

            Direct experience with the WISC-IV has suggested that the pro forma prediction of WISC-IV scores based upon the WISC-III for many children does not work. This difficulty is largely due to what has been coined “the apples and oranges effect.” The WISC-IV and the WISC-III are different in their composition, and they cannot be compared easily on the surface in a meaningful fashion.

These differences between the WISC-IV and the WISC-III become more apparent when assessing the abilities of children with learning disabilities, i.e. those who will, by definition, have greater variation in their skill levels.  Some children, such as those with weaknesses in acquired knowledge (Information and Arithmetic) may earn scores on the WISC-IV that are significantly higher than the WISC-III due to the decreased focus of the WISC-IV on knowledge that is generally acquired in school. On the other hand, given the increased WISC-IV emphasis on the ability to solve novel problems, children with pronounced weaknesses in nonverbal fluid reasoning (Matrix Reasoning and Picture Concepts) may be dismayed to find that their IQ scores have dropped. [additional information to be provided in chart] For the evaluator, these differences present a challenge with respect to how to interpret WISC IQ scores over time. 

            What is an evaluator to do? Certainly, the temptation to compare a WISC-IV Full Scale IQ with that of the WISC-III is overwhelming, and some teams are now in the awkward position of predicting achievement in a child who has now been determined to have less intellectual horsepower than he or she did a few grade levels prior. Conversely, other teams may find that they have to explain why it would be appropriate to revise their earlier estimation and increase expectations and programming for children who have now been declared to be more intelligent.

Clearly, we cannot compare apples and oranges, and a WISC is not a WISC is not a WISC. Please see the chart entitled, “Changes in the Composition of the Wechsler Intelligence Scale for Children, Fourth Edition.” The composition of the WISC-IV Full Scale IQ has changed by fifty percent.   Changes in the composition of WISC-IV Verbal Comprehension, Perceptual Reasoning, and Working Memory Scales vary from a not insignificant twenty-five percent to a wholly unrecognizable seventy-four percent; these figures, of course, presume that we have not engage in “subtest roulette.”[2] Only Processing Speed remains intact. 

For those wishing to examine the question of progress over time, the only option is to examine performance with respect to individual subtest scores (and their confidence bands). When there appears to be a decrease in scores, concerned team members are then faced with the prospect of examining why that change has occurred, and ruling out the possibility that medical concerns or nonacademic factors may be compromising a child’s ability to demonstrate what he or she knows.


[1] Technical Manual, p. 63   [2] Ron.Dumont.

Changes in the Composition of the Wechsler Intelligence Scale for Children, Fourth Edition

Subtests

Full Scale IQ

Verbal Comprehension

Perceptual Reasoning[1]

Working Memory[2]

Processing Speed

 

WISC-III

WISC-IV

WISC-III

WISC-IV

WISC-III

WISC-IV

WISC-III

WISC-IV

WISC-III

WISC-IV

Similarities

10%

10%

25%

33%

 

 

 

 

 

 

Vocabulary

10%

10%

25%

33%

 

 

 

 

 

 

Comprehension

10%

10%

25%

33%

 

 

 

 

 

 

Information

10%

0%

25%

0%

 

 

 

 

 

 

Word Reasoning

 

 

 

 

 

 

 

 

 

 

Block Design

10%

10%

 

 

25%

33%

 

 

 

 

Picture Concepts

0%

10%

 

 

0%

33%

 

 

 

 

Matrix Reasoning

0%

10%

 

 

0%

33%

 

 

 

 

Picture Completion

10%

0%

 

 

25%

0%

 

 

 

 

Object Assembly

10%

0%

 

 

25%

0%

 

 

 

 

Picture Arrangement

10%

0%

 

 

25%

0%

 

 

 

 

Digit Span

0%

10%

 

 

 

 

50%

50%

 

 

Letter-Number

Sequencing

 

 

 

 

 

 

0%

50%

 

 

Arithmetic

10%

0%

 

 

 

 

50%

0%

 

 

Coding

10%

10%

 

 

 

 

 

 

50%

50%

Symbol Search

0%

10%

 

 

 

 

 

 

50%

50%

Cancellation

 

 

 

 

 

 

 

 

 

 

Percentage of Change

 

50%

 

25%

 

74%

 

50%

 

0%


 

[1] Perceptual Organization on the WISC-III

[2] Freedom from Distractibility on the WISC-III

Some Examples of Comparisons Between WISC-III and WISC-IV Scores if Subtest Scores Were Identical on Both Tests

( ) = not included in Index or FSIQ scores    -- = not part of the test

 

all 10s

reasoning > knowledge

pictorial > puzzles

reasoning > processing

processing > reasoning

weakness in fluid reasoning & working memory

 

WISC-III

WISC-IV

WISC-III

WISC-IV

WISC-III

WISC-IV

WISC-III

WISC-IV

WISC-III

WISC-IV

 

 

 

 

 

 

 

 

 

 

 

Similarities SI

  10

  10

  13

  13

  13

  13

    7

    7

  10

  10

Vocabulary VO

  10

  10

    7

    7

  13

  13

    7

    7

  10

  10

Comprehension CO

  10

  10

  13

  13

  13

  13

    7

    7

  10

  10

(Information IN)

  10

  (10)

    7

    (7)

  13

  (13)

    7

    (7)

  10

  (10)

(Word Reasoning WR)

  --

  (10)

  --

  (13)

  --

  (13)

  --

    (7)

  --

  (10)

VCI

100

  99

100

104

117

116

  84

  83

100

  99

 

 

 

 

 

 

 

 

 

 

 

Block Design BD

  10

  10

    7

    7

  13

  13

    7

    7

  10

  10

Picture Concepts PCn

  --

  10

  --

   13

  --

  13

  --

    7

  --

    7

Matrix Reasoning MR

  --

  10

  --

    7

  --

  13

  --

   7

  --

    4

(Picture Completion PCm)

  10

  (10)

  13

  (13)

  13

  (13)

   7

   7

  10

  (10)

Picture Arrangement (PA)

  10

  --

  13

  --

  13

  --

   7

  --

  10

  --

Object Assembly (OA)

  10

  --

    7

  --

  13

  --

   7

  --

  10

  --

PRI/POI

100

100

100

  94

119

119

  83

  82

100

  82

 

 

 

 

 

 

 

 

 

 

 

Arithmetic (AR)

  10

  10

 

 

    7

    7

  13

  13

    4

    4

Digit Span (DS)

  10

  10

 

 

    7

    7

  13

  13

    4

    4

(Number Letter Seq. LN)

  10

  (10)

 

 

  --

    (7)

  --

  (13)

  --

    (4)

WMI/FDI

101

  99

 

 

  84

  83

118

116

  67

  65

 

 

 

 

 

 

 

 

 

 

 

Coding (CD)

  10

  10

 

 

    7

    7

  13

  13

  10

  10

Symbol Search (SS)

  10

  10

 

 

    7

    7

  13

  13

  10

  10

(Cancellation CA)

  --

  (10)

 

 

  --

    (7)

  --

  (13)

  --

  (10)

PSI

101

100

 

 

  86

  83

117

118

101

100

 

 

 

 

 

 

 

 

 

 

 

FSIQ

100

100

 

 

112

105

  88

  95

  96

  84