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Differential Ability Scales (DAS)


VALIDITY OF THE DAS

The DAS Introductory and Technical Handbook (The Psychological Corporation, 1990) presents studies that focus on the concurrent, and construct validity of the DAS. These studies are summarized below.

Criterion Validity

The degree to which a test is related to an established criterion measure, when both instruments are administered at approximately the same time, reflects concurrent validity. The DAS Introductory and Technical Handbook, pp. 217-241, reports the findings of a series of studies in which the DAS was given along with the Wechsler Preschool and Primary Scale of Intelligence-Revised (WPPSI-R; Wechsler, 1989), Wechsler Intelligence Scale for Children-Revised (WISC-R; Wechsler, 1974) Stanford-Binet: Fourth Edition (SB:FE; Thorndike, Hagen, & Sattler, 1986), McCarthy Scales of Children’s Abilities (MSCA; McCarthy, 1972), and the Kaufman Assessment Battery for Children (KABC; Kaufman & Kaufman, 1983). Below is a summary of some of those studies. These findings are based on relatively small samples with predominantly average ability and should not be generalized to individuals at the relative extremes of the intelligence distribution.

Preschool level of the DAS:

DAS and WPPSI-R. A sample of 62 children between ages 4 years 6 months and 5 years 11 months was administered the DAS and WPPSI-R within a 1- to 6-week period. The average retest interval was 14 days. The group was predominantly Caucasian (88 percent Caucasian, 8 percent African American, 2 percent Hispanic, 2 percent other) and composed of an equal number of males and females. The correlations between the composite scores indicated that the two batteries shared much in common. The CGA and the WPPSI-R Full Scale correlated .89, while the Verbal cluster of the DAS correlated with the Verbal IQ of the WPPSI-R .74 and the DAS Nonverbal cluster correlated with the WPPSI-R Performance Scale .75. All DAS core subtests correlated with the WPPSI-R Full Scale above .4 (median = .65) and ranged from a low of .45 for Picture Similarities to a high of .80 for Verbal Comprehension. The correlations between the diagnostic subtests and the WPPSI-R IQ scales were generally low (below .4) with the exception of the Matching Letter-like Forms subtests (range .51 to .61). The lower correlations were expected given the low g loading of the diagnostic subtests, which do not contribute to the GCA.

The DAS Verbal, Nonverbal, and GCA scores were generally lower than the WPPSI-R Verbal, Performance, and Full Scales. The average difference was 3.6 points on the Verbal Scales (97.6 vs. 101.2), .9 points on the Nonverbal vs. Performance Scales (99.0 vs. 99.9) and 2.7 points on the GCA vs. Full Scale (98.3 vs. 101.0). These differences are about what we would predict from the general rise in IQ test scores among children in the western world (Flynn, 1998). These differences fit that expected pattern better than do the differences between the WPPSI-R and WISC-III (see Chapter XX).

A sample of 23 Louisiana children between the ages of 3 years 6 months and 5 years 11 months was administered the DAS and WPPSI-R within a 56- to 106-day period. The average retest interval was 74 days. The group was predominantly Caucasian (70 percent Caucasian, 30 percent African American) and composed of approximately equal numbers of males and females. The correlations between the composite scores again indicated that the two batteries shared much in common. The CGA and the WPPSI-R Full Scale correlated .81 while the Verbal cluster of the DAS correlated with the Verbal Scale of the WPPSI-R .75 and the DAS Nonverbal cluster correlated with the WPPSI-R Performance Scale .80. All DAS core subtests correlated with the WPPSI-R Full Scale above .4 (median = .57) and ranged from a low of .41 for Pattern Construction to a high of .64 for Naming Vocabulary. The correlations between the diagnostic subtests and the WPPSI-R IQ scales were low (.22 and .36).

The DAS Verbal, Nonverbal, and GCA scores were generally lower than the WPPSI-R Verbal, Performance, and Full Scales. The average difference (DAS vs. WPPSI-R) was 3.6 points on the Verbal Scales (94.1 vs. 97.7), no difference on the Nonverbal vs. Performance Scales (99.0 vs. 99.0) and 1.4 points on the GCA vs. Full Scale (96.5 vs. 97.9).

DAS and SB:FE. The DAS and SB:FE were administered in counterbalanced order to a sample of 58 children aged 4 years 0 months to 5 years 11 months (mean = 5 years 0 months). The interval between the two test administrations ranged from 1 to 43 days (M = 9 days). The group was predominantly Caucasian (93 percent Caucasian, 7 percent African American) and composed of an approximately equal numbers of males (46%) and females (54%).

The DAS CGA and the SB:FE Composite correlated .77, while the Verbal cluster of the DAS correlated highest with the Verbal Reasoning Composite of the SB:FE (r =.72). The DAS Nonverbal cluster correlated higher with the SB:FE Abstract-Visual Reasoning score (r = .64) than with any other SB:FE score other than the overall Composite score.

The SB:FE Verbal Reasoning, Abstract-Visual Reasoning, Quantitative Reasoning, Short-term Memory, and Composite scores were generally close to or slightly above the DAS Verbal, Nonverbal, and GCA scores. The average difference (DAS vs. SB:FE) was 4.5 points on the Verbal vs. Verbal Reasoning scores (104.5 vs. 109.0), 5.2 points for the Nonverbal vs. Abstract-Visual Reasoning scores (101.9 vs. 107.1), and 2.4 points for the GCA vs. Composite scores (104.5 vs. 106.9). These results suggest that the two scales yield comparable overall scores.

DAS and the MSCA. Forty-nine British preschool children (ages 3 years 4 months to 3 years 7 months) were administered both the DAS and the McCarthy Scales of Children’s Abilities within an unspecified time frame. The children were divided into two groups: Lower Preschool (n = 49) and Upper Preschool (n = 40) for analysis purposes. For the younger group (3:4-3:7), the DAS GCA correlated well with the General Cognitive Index (GCI) score of the MSCA (r = .76). The mean difference between the overall scores was approximately 7.2 points, with the MSCA higher.

For the older group (3:6-3:7), the DAS GCA again correlated well with the General Cognitive Index (GCI) score of the MSCA (r = .82). The mean difference between the overall scores was approximately 7.7 points, with the MSCA higher. The differences between the GCA and the GCI mean score for both groups is consistent with expectations based on the 18-year difference between the standardization of the two tests (Flynn, 1998).

DAS and the K-ABC. The K-ABC was given to 23 Louisiana children of ages 3 years 6 months through 5 years 11 months (70% Caucasian, 30% African American, 52% Female, 48% Male) 62 to 111 days (M = 74 days) before they were given the DAS. Correlations of the K-ABC with the DAS were lower than correlations of the WPPSI-R DAS (GCA vs.MPC = .68), and the MPC was 4.9 points higher than the CGA.

School-Age level of the DAS:

DAS and WISC-R. Two samples, one composed of 66 children aged 8:0 to 10:2 administered the two tests between 1 to 63 days apart (M= 16 days) and the other composed of 60 adolescents between 14 years 0 months and 15 years 11 months years of age administered the two tests between 5 to 32 days apart (m = 21 days), were administered the DAS and WISC-R.

For the younger group, all of the DAS composites correlated highly with the WISC-R Full Scale IQ (range .68 to .84). The DAS Verbal score correlated highest with the WISC-R Verbal IQ (.84), while the DAS Nonverbal Reasoning score correlated higher with the WISC-R Verbal than with the Performance (.77 vs. .57). The DAS Spatial cluster correlated highest with the WISC-R Performance scale (.69).

The DAS Verbal, Nonverbal, Spatial, and GCA scores were generally lower than the WISC-R Verbal, Performance, and Full Scales. The average difference between the GCA and the Full Scale IQ was 8.1 points (107.2 vs. 115.3) and probably reflects the differences that occur because of the interval between the standardization of the two tests (Flynn, 1998).

For the older group, very similar results were found. All of the DAS composites correlated well with the WISC-R Full Scale IQ (range .59 to .91). The DAS verbal score correlated highest with the WISC-R Verbal IQ (.84) while the DAS Nonverbal Reasoning score correlated almost equally well with both the Verbal and Performance scales of the WISC-R (.68 and .69 respectively). The DAS Nonverbal Reasoning score also showed a correlation of .69 with the WISC-R "Third Factor . . . calculated by the formula provided by Sattler (1988, p. 816)" (Elliott, 1990b, p. 228). For older students, the DAS Nonverbal Reasoning subtest, Sequential and Quantitative Reasoning, requires extensive mental arithmetic. The correlation between the DAS Sequential and Quantitative Reasoning and the WISC-R Arithmetic subtests was .81. Subtests involving mental arithmetic make up one-third of the WISC-R "Third Factor" and one-half of the DAS Nonverbal Reasoning cluster. The DAS Spatial cluster correlated highest with the WISC-R Performance scale (.77).

Again, the DAS Verbal, Nonverbal, Spatial, and GCA scores were generally lower than the WISC-R Verbal, Performance, and Full Scales. The average difference between the GCA and the Full Scale IQ was 5.7 points (100.5 vs. 106.2) and again probably reflects the differences that occur because of the interval between the standardization of the two tests (Flynn, 1998).

DAS and WISC-III. The WISC-III manual (Wechsler, 1991) presents a sample of 27 children aged 7 to 14 administered the two tests.

For the group, all of the DAS composites correlated highly with the WISC-III Full Scale IQ (range .71 to .92). There was a high (.92) correlation between the DAS GCA and the WISC-III Full Scale IQ. The DAS Verbal score correlated highest with the WISC-III Verbal IQ (.87) while the DAS Nonverbal Reasoning score correlated higher with the WISC-III Performance than with the Verbal (.78 vs. .58). The DAS Spatial cluster correlated highest with the WISC-III Performance scale (.82).

The DAS Verbal, Nonverbal, Spatial, and GCA scores were slightly lower than the WISC-III Verbal, Performance, and Full Scales. The average difference between the GCA and the Full Scale IQ was 2.1 points (103.4 vs. 105.5) and may reflect the differences in the constructs measured by the two tests.

Dumont, Cruse, Price, & Whelley (1996) examined the relationship between the DAS and WISC-III for a sample of 53 children identified as having a learning disability. Each of the children had been administered the WISC-III and approximately 3 years later, was administered the DAS.

For this group, all of the DAS composites correlated moderately with the WISC-III Full Scale IQ (range .64 to .78). There was a high (.78) correlation between the DAS GCA and the WISC-III Full Scale IQ. The DAS Verbal score correlated highest with the WISC-III Verbal IQ (.77), while the DAS Nonverbal Reasoning score correlated higher with the WISC-III Performance than with the Verbal (.55 vs. .65). The DAS Spatial cluster correlated highest with the WISC-III Performance scale (.67).

The DAS Verbal, Nonverbal, Spatial, and GCA scores were slightly lower than the WISC-III Verbal, Performance, and Full Scales. The average difference between the GCA and the Full Scale IQ was 2.4 points (87.2 vs. 89.7) and may reflect the differences in the constructs measured by the two tests.

DAS and SB:FE. The DAS and SB:FE were administered in counterbalanced order to a sample of 55 children aged 9 years 0 months to 10 years 11 months (mean = 9 years 11 months). The interval between the two test administrations ranged from 1 to 62 days (M = 11 days). The group was predominantly Caucasian (i.e., 85 percent Caucasian, 11 percent African American, and 4 percent Hispanic) and composed of an approximately equal numbers of males (55%) and females (45%).

The DAS CGA and the SB:FE Composite correlated .88, while the Verbal cluster of the DAS correlated highest with the Verbal Reasoning Composite of the SB:FE (r =.79). The DAS Nonverbal Reasoning cluster showed a strong relationship with both the SB:FE Abstract-Visual Reasoning (r = .76) and the Quantitative Reasoning (.75), while the DAS Spatial correlated best with the SB:FE Abstract Visual Reasoning (.67).

The SB:FE Verbal Reasoning, Abstract-Visual Reasoning, Quantitative Reasoning, Short-term Memory, and Composite scores were generally close to or slightly above the DAS Verbal, Nonverbal, and GCA scores. The average difference (DAS vs. SB:FE) was 5.8 points on the Verbal vs. Verbal Reasoning scores (103.8 vs. 109.6), 3.1 points for the Nonverbal Reasoning vs. Abstract-Visual Reasoning scores (104.8 vs. 107.9), 2.1 points for the Nonverbal Reasoning vs. Quantitative Reasoning scores (104.8 vs. 106.9), 5.1 points for the Spatial vs. Abstract-Visual Reasoning scores (102.8 vs. 107.9), and 3.5 points for the GCA vs. Composite scores (106.3 vs. 109.8). These results suggest that the two scales yield comparable overall scores.

DAS and WJ-R. Dumont, Willis, Farr, McCarthy, & Price (2000) administered the DAS and WJ-R to 81 children (47 males, 34 females; 78 Caucasian, 3 African American; ages 6 years 6 months to 17 years 8 months) referred for special education services evaluation. The WJ-R BCA-STD correlated .65 with the DAS GCA, .64 with the DAS Verbal, .50 with the DAS Nonverbal Reasoning, and .51 with the DAS Spatial clusters. Mean differences (DAS vs. WJ-R BCA-STD) were -2.80 (GCA), -0.74 (Verbal), -6.07 (Nonverbal Reasoning), and 0.84 (Spatial). Dumont et al. (2000, p. 36) characterized the correlation between the CGA and BCA-STD as significant, but only moderate. Some, but not all of the correlations between DAS and WJ-R subtests conformed to predictions based on broad and narrow ability classifications from the McGrew, Flanagan, and Ortiz Integrated Carroll/Cattell-Horn Gf-Gc theory (McGrew & Flanagan, 1998). Dumont et al. caution against the assumption that subtests purporting to measure the same broad and narrow abilities will actually yield comparable scores for any individual.

Based upon the correlations across the different measures, it appears that the DAS has satisfactory concurrent validity. For the most part, the DAS GCA correlates more highly with other measures of intelligence (M r = .83) than it does with tests of academic achievement (M r = .58.)

Construct Validity

One method of assessing construct validity is factor analysis. Factor analysis can be used to determine the structure and components of intelligence as measured by a given test. The pattern of intercorrelations discussed below provides evidence of convergent and discriminant validity, which are forms of construct validity. Convergent validity is demonstrated when tasks that theoretically tap similar functions correlate more highly with each other than with tasks that theoretically measure different functions. Discriminant validity is demonstrated when tasks that purport to measure different functions yield relatively low or nonsignificant correlations when they are correlated with each other.

There is strong evidence that the DAS yields both a measure of general intelligence and specific factors as noted in studies reported in the DAS manual.

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Intercorrelations