Abstract
The study of equivalence relations exhibited by individuals with mental retardation and language limitations holds the promise of providing information of both theoretical and practical significance. We reviewed the equivalence literature with this population, defined in terms of subjects having moderate, severe, or profound mental retardation. The literature includes 55 such individuals, most of whom showed positive outcomes on equivalence tests. The results to date suggest that naming skills are not necessary for positive equivalence test outcomes. Thus far, however, relatively few subjects with minimal language have been studied. Moreover, we suggest that the scientific contributions of studies in this area would be enhanced with better documentation of language skills and other subject characteristics. With recent advances in laboratory procedures for establishing the baseline performances necessary for equivalence tests, this research area is poised for rapid growth.