Operant variability: Evidence, functions, and theory Although
responses are sometimes easy to predict, at other times
responding seems highly variable, unpredictable, or even random.
The inability to predict is generally attributed to ignorance of
controlling variables, but this article is a review of research
showing that the highest levels of behavioral variability may
result from identifiable reinforcers contingent on such
variability. That is, variability is an operant. Discriminative
stimuli and reinforcers control it, resulting in low or high
variability, depending on the contingencies. Schedule-of-
reinforcement effects are orderly, and choosing to vary or
repeat is lawfully governed by relative reinforcement
frequencies. The operant nature of variability has important
implications. For example, learning, exploring, creating, and
problem solving may partly depend on it. Abnormal levels of
variability, including those found in psychopathologies such as
autism, depression, and attention deficit hyperactiv