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Differential Ability Scales (DAS)


Step-by-step Analysis

Before interpretation can focus on the clusters themselves, Step 4 (Figure-7) must be completed to determine how unified the cluster scores are. If the subtests' T scores that create the individual clusters are very different from each other, then the Composite Cluster scores will have little intrinsic meaning, and should not be interpreted as a unitary construct. For Kate, Step 4 indicates that the subtests within the Verbal and within the Spatial Clusters are close to one another and show no significant differences. However, the subtests in the Nonverbal Reasoning Cluster differ by 11 points and this difference is statistically significant. Base rate suggests that approximately 15% of children obtain a difference of this magnitude.

Figure-7 DETERMINING WITHIN-CLUSTER DIFFERENCES

DIFF.

STATISTICALLY SIGNIFICANT

ABNORMAL

FREQUENCY (Table B.3. p. 291)

WDef vs. Sim (12 pts) :

7

Y / N

Y / N

in ____ % of the population.

Mat vs. SQR (11 pts) :

11

Y / N

Y / N

in _15__ % of the population.

RDes vs. PCon (10 pts) :

0

Y / N

Y / N

in ____ % of the population.

Because of the significant, though not highly unusual, differences between the Matrices and Sequential & Quantitative Reasoning subtests, the narrow abilities assessed by each subtest should be considered. In this case, Matrices being so much higher than the Sequential & Quantitative Reasoning may indicate a difference between Kate's abilities in the area of Induction versus Quantitative Reasoning. Induction refers to the ability to discover underlying rules, concepts, processes, trends, and/or class memberships that governs a particular problem, while Quantitative Reasoning refers to the ability to inductively or deductively reason with concepts involving mathematical relations and properties. Qualitative analysis of Kate's responses on the Sequential & Quantitative Reasoning subtest may provide evidence to explain this difficulty. Were her answers incorrect because of a lack of reasoning (not understanding the logical reasoning being the problems), were they incorrect because of an inability to problem-solve when the stimuli involved numerical concepts, or did she simply make computational errors?

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Case Study, p. 5