Abstract
Study objectives: The purpose of the present paper is to describe the concept of operant variability. Operant variability is difficult to explain because of its abstract nature. In order to elucidate this concept and distill the axes of previous studies, a preliminary discussion covered: (1) usage of the concepts of operant and variability in behavior analysis, and (2) an analysis of procedures that studies in this area often use. Next, published research examining the validity of variability as an operant was discussed in terms of the relation between differential reinforcement and behavioral variability. Conclusion: Operant behavior does not have a dimension of variability that can be a target of differential reinforcement, but it does have that dimension as an internal parameter of the behavior.