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Differential Ability Scales (DAS)


Step-by-step Analysis

An Illustrative Case with the DAS

Kate, a 14 year old, was referred for evaluation because of difficulty in her 8th grade classes, specifically in the areas related to mathematical concepts and reasoning. Teachers had noted on the Learning Disabilities Diagnostic Inventory (LDDI, 1999) that she frequently "Makes borrowing errors," "Reaches 'unreasonable' answers," and "Has difficulty in multi-step problems."

Kate was administered the DAS and obtained the results in T scores, Standard Scores, and Percentile Ranks for her age found in Table - 26.

 

Table -

Table - 26  KATE’S DAS SCORES AS T SCORES, STANDARD SCORES, AND PERCENTILE RANK FOR HER AGE

Total Scores
[letters in ( ) show subtests from below included in each Composite]

Standard Score

Percentile Rank

Classification

95% Confidence1

General Conceptual Ability

(WDef Sim Mat SQR RDes PCon)

100

50

Average

91-109

Verbal

(WDef Sim)

103

58

Average

93-113

Nonverbal Reasoning

(Mat SQR)

78

07

Low

70-88

Spatial

(RDes PCon)

116

86

Above Average

107-124

 

T Score

Percentile Rank

Classification

 

Verbal Tests

Words Definitions (WDef)

49

46

Average

Similarities (Sim)

56

73

Average

Nonverbal Tests

Matrices (Mat)

43

24

Average

Sequential & Quantitative Reasoning (SQR)

32

04

Low

Spatial Tests

Recall of Designs (RDes)

60

84

High

Pattern Construction (PCon)

60

84

High

Diagnostic Tests

Recall of Digits (RDig)

30

02

Low

Recall of Objects - Immediate (ROi)

55

69

Average

Recall of Objects - Delayed (ROd)

61

86

Above Average

Speed of Information Processing (SIP)

35

07

Low

  1. Even the best tests are not perfectly consistent. Lucky and unlucky guesses or barely beating or missing time limits, for example, will cause scores to vary. The 95% confidence band shows how much scores are likely to vary 95% of the time by pure chance.

WDef = Word Definitions, Sim = Similarities, Mat = Matrices, SQR = Sequential & Quantitative Reasoning, RDes = Recall of Designs, PCon = Pattern Construction, RDig = Recall of Digits, ROi = Recall of Objects-Immediate, ROd = Recall of Objects-Delayed, SIP = Speed of Information Processing

The first step in interpreting Kate's results is an examination strictly from a descriptive point of view - at what level of cognitive ability what did she perform? Analysis at this stage is considered descriptive in nature since no statistical comparisons have yet been made. Kate appears to be functioning overall in the Average range, with a GCA score of 100 (94-106, 59th percentile, Average). The GCA score comprises her other composite scores, and these scores range from the low Nonverbal Reasoning score of 78 (70-88, 10th percentile, Low) to her high Spatial score of 116 (107-124, 81st percentile, High). Because of the differences between the scores, a careful analysis of Kate's profile is warranted. Blindly accepting the perfectly Average GCA score would neglect to take into consideration the seemingly diverse nature of Kate's abilities.

Examining the subtest T scores also gives some preliminary description about how Kate performed. Her core subtests ranged from a low of 32 (10th percentile) on the Sequential & Quantitative Reasoning subtest to a high of 60 (84th percentile) on the two Spatial subtests, Recall of Designs and Pattern Construction. The scores on the diagnostic subtests given to Kate also reveal information from which to generate hypotheses. She did poorly on both the Recall of Digits (2nd percentile) and Speed of Information Processing (7th percentile) and yet performed average or above on both the Recall of Objects - Immediate (69th percentile) and - Delayed (86th percentile) subtests. Since Recall of Digits and Recall of Objects both involve some aspect of memory, this area will need to be further explored throughout the interpretation.

To continue the analysis of Kate's scores, examiners should complete each of the steps outlined in the previous section of this chapter. Completing these steps allows the hypothesis generation and resulting interpretation to be integrated with all findings instead of continually generating hypotheses in one step that might be quickly negated by the next step. For our example, the DAS Analysis Sheet (Exhibit-4) was completed.

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Case Study, p. 2