Diagnostic and classification accuracy for mildly mentally handicapped children
Creators: name: Carter, David E.
Publisher: name: University of British Columbia
Year: 2011

description: The purpose of this study was to examine the diagnostic and classification accuracy of placement decisions for Mildly/Educably Mentally Handicapped (M/EMH) children in British Columbia. Evidence from the United States suggests that classification decisions are often made on the basis of idiosyncratic student behaviours and the subjective opinions of educators, not on the basis of empirical evidence. Although Canadian special education practice is often based on that of the U.S., no major study of the accuracy of diagnosis and classification has been undertaken in this country. Based on a review of the literature, internationally accepted criteria for the diagnosis and classification of M/EMH students were formulated. In addition, variables that might influence the use of these criteria were identified. Elementary age students from two metropolitan Vancouver school districts who had been suspected of being M/EMH during a two-year period served as subjects (n=106). Of these 57 were classififed as M/EMH and 49 were classified as regular education. An evaluation of IQ, adaptive behaviour, reading and arithmetic achievement, maladaption, and visual and hearing acuity was performed for each subject. Preliminary data analyses permitted the formation of an achievement composite score and the pooling of subjects from the two districts. Using an internationally accepted two-factor diagnostic model, analyses were performed to investigate the classification accuracy for the sample. Cut-off criteria used with the two-factor model were adjusted to those of both the American Association for Mental Deficiency and the draft B.C. Special Education Guidelines. Where subjects could not be confirmed by the application of these models, sources of classification error were identified. Next, a series of discriminant function analyses, each representing a historical step in the development of diagnostic and classification models, were performed and the classification accuracy of each examined. Finally, a full model of all measured variables was examined using both a forced discriminant function procedure and a step-wise technique. The findings suggested that a combination of the adaptive behaviour, IQ, and achievement variables provided the highest classification accuracy. This result is consistent with much of the research from the U.S. IQ scores were found to consistently dominate classification decisions. In addition, academic achievement proved to be a valid predictor, either in combination with social adaptation or maladaption. However, maladaptive behaviour, whenever entered with social adaptation, overwhelmed the latter as a descriminator of group membership. The highest classification rate for the total sample was 92.0% for the combination of adaptive behaviour, IQ, and academic achievement. Although visual and hearing acuity were not found to be related to group membership, it was discovered that testing for these variables was not occurring in the districts studied in accordance with accepted best practice. A disproportionate number of M/EMH students proved to be untestable using school-based audiological and visual sweep testing techniques. In cases of untestability, the assumption that the child can see and hear within normal tolerances appears to be made, and efforts to use alternative testing procedures are not pursued. In addition, visual and hearing testing appears to occur after the administration of standardized cognitive tests, and not before, as best practices would dictate. The principal contributions of this research are (1) that it is the first major study of diagnostic and classification accuracy with a Canadian M/EMH population, (2) that it advises the inclusion of academic achievement as a domain of adaptive behaviour based on empirical evidence of the importance of that variable in diagnosing M/EMH, and (3) it examines the role of auditory and visual acuity testing in M/EMH diagnosis and classification.