Factor analytic studies of the WISC (Wechsler, 1949) by Baumeister and Bartlett (1962a, 1962b) and Wallbrown, Blaha, Wherry, and Counts (1974) are noteworthy since they involve the use of hierarchical analysis (Wherry, 1959; Wherry and Wherry, 1969) for testing cognitive structure hypotheses derived from psychological theory. These studies are also similar in that they represent an attempt to investigate a major presupposition which has long figured prominently in assessment theory and practice: that is, individuals within an established syndrome should demonstrate a common pattcrn of cognitive anomalies which is distinguishable from that of normals.
The study by Wallbrown, Blaha, Wherry, and Counts (1974) involved this presupposition, since three cognitive structure hypotheses derived from the work of RIyklebust, Bannochie, and Killen (1971) were investigated through an hierarchical factor analysis of t.he WISC for normal and reading disabled children. Comparison of the ability structure for these groups provided strong support for two of the three hypotheses; that is, the ability structure for reading disabled children was distinguishable from that of normals by less effective ability integration as well as a more complex overall ability arrangement. The ability organization hypothesis was not supported, however, since communality estimates for the two groups were comparable.
The Wherry and Wherry (1969) hierarchical factor solution mentioned above is especially useful for testing cognitive structure hypotheses, since it not only identifies the basic ability dimensions, but also indicates the structural relationships among these dimensions. A detailed treatment of the Wherry and Wherry (1969) solution is beyond the scope of the present endeavor, but more detailed descriptions are available ekewhere (Hayncs, 1970; Wallbrown, Blaha, and Wherry, 1973, 1974; Wherry, 1959).
The purpose of the present study was to investigate further the validity of three cognitive structure hypotheses which were formulated by Myklebust, Bannochie, and Killen for the overall field of learning disabilities. Reading disability may be considered legitimately as a subset of the broader field of learning disability. Consequently, these hypotheses can be stated operationally in terms of hierarchical theory for the area of reading disability. Specifically, the mental abilities of severe reading disabled children, as indicated by the WISC, are different from the abilities of normals with respect to the following parameters: (a) different overall ability arrangement, as indicated by the hierarchical factor structure for subteats; (b) less effective ability integration, as indicated by a smaller proportion of subtest variances attributable to the g-factor; and (c'l less ability organization, as indicated by communality estimates.
METHOD
Data for the present study consisted of WISC subtest intercorrelations for Subtest intercorrelations for normal Ss normal and severe reading disabled Ss.