tional or behavioral problems that are so severe that they interfere with adaptation or academic achievement (i.e., emotional disturbance). Making that differential diagnosis without using tests of intelligence raises a host of issues. We turn now to the second behavioral dimension defining MR, adaptive behavior.
The second behavioral dimension defining MR, impairments in adaptive behavior or adaptive skills, presents more serious psychometric problems to those conducting the assessment, particularly when applied to those with MMR. Even when the Heber definition was dominant, which would permit approximately 16 percent of the general population having IQ scores of 85 or below to be classified as MR, no more than 1 percent of the general population was identified as MR (Mercer, 1973a, b; Tarjan et al., 1973). The reason for the discrepancy was that the schools and other clinicians never used IQ alone to define MR; two dimensions were always considered in making a diagnosis (impairments in adaptive behavior and subaverage general intellectual functioning). In fact, these two criteria were applied sequentially: (a) impairments in adaptation and then (b) subaverage general intellectual functioning. Only children referred by their classroom teachers were ever evaluated on the intellectual dimension. A huge percentage of those who would have scored below IQ 85 were never referred, and even among those who were, only a small percentage were ever certified as eligible for services. In fact, some of those referred were protected from certification as a result of the psychoeducational assessment provided.
Ashurst and Meyers (1973) also examined data from the Riverside study reported by Mercer (1973a). They examined 269 cases of children referred for severe and persistent academic underachievement. Of interest to the current discussion is how referred cases were deemed eligible or ineligible by school psychologists and then how admissions and dismissal committees arrived at decisions in light of: (a) teacher referral data, and (b) psychologist certification that the child was eligible or ineligible. Five different results were identified and the number of cases fitting a given “result” noted:
Teacher referred, psychologist found child eligible, child placed as MMR (86 children).
Teacher referred, psychologist found child eligible, child not placed (63 children).
Teacher referred, psychologist found child ineligible, child not placed (116 children).