The DAS, like many other standardized cognitive ability tests, uses the
Deviation IQ (M = 100, SD = 15) for the Verbal, Nonverbal,
Nonverbal Reasoning, Spatial, and General Conceptual Ability composite scores
and T scores (M = 50, SD = 10) for the 17 individual subtests. The
calculation of the DAS scores involves a 3-step process. After each subtest is
scored, raw point totals are converted to Rasch-type "ability scores."
These ability scores provide a raw level of performance on the individual
subtest, based on the number of correct item responses and the difficulty of the
items administered. Each subtestís ability score is then converted to a T
score with a range from 20 to 80. From the sums of the T scores for the subtests that create clusters,
the examiner obtains the standard scores for the clusters of the test. Finally,
the T scores obtained for the respective clusters are added and this sum is used
to obtain the GCA score. To convert ability scores to T scores within the
examinee's own age group, use Table 1 in the DAS Administration and Scoring
Manual (Elliott, 1990; pp. 280-373). Age groups are 2-month intervals for
children 2 years 6 months to 7 years, 11 months, and 6-month intervals for
children 8 years and older.
Tables 2 and 3 (pp. 374 - 384) in the DAS Administration and
Scoring Manual are used to obtain Cluster and GCA scores based on the
battery-appropriate standard subtests. If the examiner takes advantage of the
opportunity to test a child older than age 5 years 11 months with the Preschool
Battery or a child younger than age 6 years with the School-Age battery, it is
essential to use the Cluster and GCA tables that correspond to the battery
actually given, not the tables for the child's age. Diagnostic subtests are
never used in the calculation of GCAs nor used as replacements for core battery
Table 11 (pp. 408-9) in the DAS Administration and Scoring Manual
provides, for the all Cognitive and Achievement subtests, age-equivalent scores
that reflect the age at which the examinee's ability score is the median score.
No age-equivalent scores are available for the clusters or the General
Conceptual Ability Scores. These scores are provided to assist the examiner in
interpreting scores on subtests that have been administered to children at ages
for which there are no norms. Extreme caution is advised whenever using or
interpreting these scores.