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Differential Ability Scales (DAS)


RANGE OF DAS SUBTEST SCALED SCORES

The DAS provides a range of T scores from 20 to 80. However, this range is not possible for all subtests at all ages of the test. Table-18 shows the ages at which a child could, on each subtest, obtain the lowest T score possible (20) and the highest T score possible (80). For the lowest T score available (20), none of the 17 subtests provides this scores at the lowest ages. (Verbal Comprehension, normed for ages 2 years 6 months to 6 years 11 months, does provide a T score of 21 at age 2 years 6 months and 20 at age 2 years 9 months). At the upper end of scores, only 6 of the 17 subtests provide the highest T score. For example, although the Sequential and Quantitative Reasoning subtest provides norms from ages 5 years 0 months to 17 years 11 months, it is possible to obtain a full range of T scores (20 to 80) only between the ages of 8 years 0 months and 13 years 5 months. A five-year-old child who is administered this subtest and fails all items, obtaining a raw score of 0, would obtain a T score of 40. Conversely, a seventeen-year-old child administered this subtest and passing all items would obtain a T score of only 70.

Table-18

Age at which the DAS Subtests Provide for the Lowest and Highest T Score

Subtest

Total Normed Age Range

Usual Age Range

Age of Lowest T Score (20)

Age of Highest T Score (80)

Block Building

2:6-4:11

2:6-3:5

3:9

3:5

Verbal Comprehension

2:6-6:11

2:6-5:11

2:9

5:2

Picture Similarities

2:6-7:11

2:6-5:11

3:9

5:11

Naming Vocabulary

2:6-8:11

2:6-5:11

3:3

6:8

Early Number Concepts

2:6-7:11

3:6-5:11

4:9

5:8

Copying

3:6-7:11

3:6-5:11

4:6

7:11

Pattern Construction

3:0-17:11

3:6-17:11

4:6

14:11

Word Definitions

5:0-17:11

6:0-17:11

7:9

17:11

Similarities

5:0-17:11

6:0-17:11

7:6

17:11

Matrices

5:0-17:11

6:0-17:11

6:3

13:5

Sequential & Quantitative Reasoning

5:0-17:11

6:0-17:11

8:0

13:5

Recall of Designs

5:0-17:11

6:0-17:11

6:6

17:11

Matching Letter-like Forms

4:0-7:11

4:6-5:11

5:9

5:2

Recall of Digits

2:6-17:11

3:0-17:11

4:0

13:11

Recall of Objects

4:0-17:11

4:0-17:11

5:0

17:11

Recognition of Pictures

2:6-17:11

3:0-7:11

4:6

7:5

Speed of Information Processing

5:0-17:11

6:0-17:11

7:6

17:11

Adapted from the Differential Ability Scales: Introductory and Technical Handbook. Copyright 1990 by The Psychological Corporation. Reproduced by permission. All rights reserved.

The failure to have the same maximum and minimum T scores at the upper and lower limits (i.e., a T score of 80 or 20) throughout the test may affect how you interpret the profiles of children. On the core subtests of the Upper Preschool battery, typically administered to children aged 3 years 6 months to 5 years 11 months, two subtests (Verbal Comprehension and Early Number Concepts) have limited ceilings, resulting in maximum T scores of 71 and 75 respectively, while 3 subtests (Early Number Concepts, Copying, and Pattern Construction) have somewhat limited floor, with minimum T scores of 30, 31, and 30 respectively (see Table-19). On the core subtests of the School-Age Battery, typically administered to children between the ages of 6 years 0 months and 17 years 11 months, three subtests (Pattern Construction, Matrices, and Sequential & Quantitative Reasoning) have insufficient ceiling scores, resulting in maximum T scores of 75, 75, and 70 respectively, while 3 subtests (Word Definitions, Similarities, and Sequential & Quantitative Reasoning) have somewhat limited floor, with minimum T scores of 30, 30, and 32 respectively (see Table-20).

Table-19

Lowest and Highest Subtest T Score Ranges on Upper Preschool Battery

Subtest

T Score Range at Lowest Usual Age (3:6)

T Score Range at Highest Usual Age (5:11)

Verbal Comprehension

20 - 80

20 - 71

Picture Similarities

21 - 80

20 - 80

Naming Vocabulary

20 - 80

20 - 80

Early Number Concepts

30 - 80

20 -75

Copying

31 - 80

20 - 80

Pattern Construction

30 - 80

20 - 80

Adapted from the Differential Ability Scales: Introductory and Technical Handbook. Copyright 1990 by The Psychological Corporation. Reproduced by permission. All rights reserved.

 

Table-20

Lowest and Highest Subtest T Score Ranges on School-Age Battery

Subtest

T Score Range at Lowest Usual Age (6:0)

T Score Range at Highest Usual Age (17:11)

Pattern Construction

20 - 80

20 - 75

Word Definitions

30 - 80

20 - 80

Similarities

30 - 80

20 - 80

Matrices

21 - 80

20 - 75

Sequential & Quantitative Reasoning

32 - 80

20 - 70

Recall of Designs

24 - 80

20 - 80

Adapted from the Differential Ability Scales: Introductory and Technical Handbook. Copyright 1990 by The Psychological Corporation. Reproduced by permission. All rights reserved.

RANGE OF DAS FULL SCALE IQS

The range of DAS GCA is 44 to 175. This range is not available at some ages. For example, the highest possible GCA that adolescents who are aged 17 years 11 months can get is 156; the lowest possible GCA that children who are 2 years 6 month old can get is 53.

Because awarding T score points for no successes might be problematic, Elliott (1990. p. 53) recommends that examiners attempt to administer subtests from a lower level of the DAS battery whenever possible. This allows examiners to administer tasks that are closer to the child's ability level. In cases where this is not possible, examiners can convert the 0 raw scores to ability and then T scores and interpret the results with extreme caution. One exception to the use of the 0 raw score is when the examiner believes that the child's performance does not accurately reflect the child's ability. In a case where a child refuses to do a task or to answer questions, the raw score would reflect the child's unwillingness to participate in the testing of that ability and not reflect the child's inability to do the task. In these cases, if only one subtest was considered invalid, the examiner might prorate the Composite based on the remaining, valid scores. When more than one subtest is considered invalid, the examiner should omit the calculation of the composite scores and restrict interpretation to the subtest level.

For children of very low ability, the DAS provides a procedure for calculation of downward extensions of the GCA. Table 5 (pp. 385-89) in the DAS Administration and Scoring Manual provides the norms for obtaining GCA scores as low as 25. In order to obtain extended GCA scores, the examiner administers the appropriate subtests for a particular level of the DAS (e.g., Upper Preschool). The examiner then converts the obtained ability scores to T scores using the usual subtest norm tables. However, the examiner uses the T score from an appropriate Reference Age Group for the level of the Cognitive Battery that was administered. The three Reference Age Groups available are 2 years 6 months to 2 years 8 months (Lower Preschool administration), 3 years 6 months to 3 years 8 months (Upper Preschool administration), and 6 years 0 months to 6 years 2 months (School-Age administration).

For example, a child of age 8 years 0 months is administered the Upper Preschool battery rather than the usual School-Age battery. The child obtains the ability scores shown in Figure 3. To calculate the T scores, the examiner uses the norm table for the Reference Age Group (3:6 - 3:8) (DAS Administration and Scoring Manual, p. 286). Using the sum of these T scores, an Extended GCA of 35 is found in Table 5. GCA Equivalents of Sums of T Scores for the Reference Age Group (p. 386 - 7).

 

Figure 3

Calculation of Extended GCA

Subtest

Ability Score

T Score from Reference Age Group (3:6 - 3:8)

Verbal Comprehension

91

43

Picture Similarities

60

48

Naming Vocabulary

75

50

Pattern Construction

65

48

Early Number Concepts

70

56

Copying

64

59

Sum of T scores

304

Extended GCA Score

35

This procedure allow examiners to administer the Lower Preschool battery to children up to the age of 6 years 11months, and the Upper Preschool battery to children up to age 13 years 11 months and still calculate T scores and Extended GCA scores.

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