An approach to analyzing a single subject's scores obtained in a standardized test with application to the aachen aphasia test (AAT)

Abstract

Methods for the analysis of a single subject's test profile(s) proposed by Huber (1973) are applied to the Aachen Aphasia Test (AAT). The procedures are based on the classical test theory model (Lord & Novick, 1968) and are suited for any (achievement) test with standard norms from a large standardization sample and satisfactory reliability estimates. Two test profiles of a Wernicke's aphasic, obtained before and after a 3-month period of speech therapy, are analyzed using inferential comparisons between (groups of) subtest scores on one test application and between two test administrations for single (groups of) subtests. For each of these comparisons, the two aspects of (i) significant (reliable) differences in performance beyond measurement error and (ii) the diagnostic validity of that difference in the reference population of aphasic patients are assessed. Significant differences between standardized subtest scores and a remarkably better preserved reading and writing ability could be found for both test administrations using the multiple test procedure of Holm (1979). Comparison of both profiles revealed an overall increase in performance for each subtest as well as changes in level of performance relations between pairs of subtests.