1) A schedule in which the last of a specified number of responses is reinforced. In a fixed-ratio (FR) schedule, the number is constant from one reinforcer to the next; performance is characterised by pauses after the reinforcer followed by a relatively high and constant response rate. In a variable-ratio (VR) schedule, the number of responses varies from one reinforcer to the next; relative to FR schedules, the postreinforcement pause is ordinarily reduced or eliminated. A VR schedule is usually identified in terms of the average ratio, the average responses per reinforcer. In the variety of VR schedule called random ratio (RR), the ratio specifies the probability with which a response will be reinforced. For example, in RR 20 that probability is .05 (1/20) and is independent of the number of responses emitted since the last reinforcer. In some VR schedules, successive ratios are selected in irregular order from a set of ratios described by a mathematical progression, analogous to those used in VI schedules).

2) Reinforcements are programmed according to the number of responses emitted by the organism.

3) Response-based schedules of reinforcement.