Identify any significant subtest variation from the Mean Core T Score
A test battery such as the DAS provides a picture of an individual's
cognitive strength and weaknesses. This type of evaluation is considered ipsative
- within the individual. As such, when evaluating the test profile, the relative
level of a subtest score, rather than the absolute level, is of great
Although subtest scores are related, they differ in item content and test
administration and thus these differences cause the subtest scores to vary. In
statistical terms, each subtest carries with it some components of shared common
variance, while most have some proportion of specific, reliable variance as well
as finally components of error variance. Subtests can, and do, differ from each
other. Before one can evaluate the differences between what appear to be high or
low subtest scores, one must evaluate whether these apparent differences are
large enough to warrant interpretation. To do so we must know if the difference
is large, reliable, and significant.
Determining an individual subtest's strength or weakness requires that one
examine how discrepant is each subtest from the full test mean. The DAS has
provided the examiner easy access to both the child's mean for the test (found
in the DAS Manual, in Tables 3 and 4) and the discrepancy requirement for
each subtest (on the protocol summary page, in the DAS Manual, Table 12,
as well as in the DAS Handbook, Table B.5.).
For statistical significance at the .05 level, the Preschool and School-Age
core subtests require between 8 to 13 points of difference between the subtest T
score and the Mean Core T score. Diagnostic subtests vary between 9 and 16
points at the .05 level.
- Identify the frequency of any observed significant differences
Tables B.6, B.7 and B.8 in the DAS Handbook provide approximate
percentages of the norm sample that obtained certain differences between the
Mean Core T score and the individual subtest scores. Using these tables allows
the examiner to determine whether the differences observed reach a level of
unusualness. Overall, for the core subtests, differences of about 11 points on
the Preschool battery and 10 points on the School-Age, would be expected to
occur in only about 10 percent of the children tested.