VI– Used in teaching and proper use of reinforcers, variable interval is a way of describing a group of different time-based schedules of reinforcement. For example, the child’s first correct response will be reinforced after 5 minutes, then after 3 minutes, then after 4 minutes. These different intervals (5 minutes, 3 minutes, and 4 minutes) will be labeled as VI-3—the average of the sum of the three intervals. Behaviors on a VI schedule tend to produce uniform or stable response rates in which larger averages produces somewhat less behaviors.