Reliability estimates for psychological tests are almost always
reported for nonclinical populations (e.g., the normative samples).
Such practice will no longer be sufficient as the new standards
for testing call for an adequate assessment of psychometric
properties within the specific population being tested. The
purpose of this study was to provide internal consistency
reliability estimates for clinical groups on the Wechsler Adult
Intelligence Scale–Third Edition. The study included data
from 403 clinical participants composed of 10 groups of adults
recruited as part of the WAIS–III clinical validity studies.
Split-half reliability coefficients were obtained for these
groups replicating the procedure used in the WAIS–III.
With 8 of the clinical groups, the split-half reliability
coefficients were comparable to, or even higher than, those
reported for the WAIS–III standardization sample. In general,
the split-half coefficients for the Verbal subtests tended to
be higher than the coefficients for the Performance subtests.
The high magnitude and general pattern of these coefficients
demonstrate that the WAIS–III scales do not include
additional error variance above and beyond what is reported
in the WAIS–III–WMS–III Technical Manual
when it was used to assess certain clinical groups. For the
ADHD/ADD and learning disabilities groups, however, the internal
consistencies coefficients of some subtests were relatively
lower, although not statistically significant, than the normative
sample. These findings may reflect more heterogeneity within
the groups. The implications for assessment and for using alternate
methods of determining the psychometric properties in these
populations are discussed. (JINS, 2001, 7,