variable ratio

Meaning: In operant conditioning, a variable-ratio (VR) schedule delivers reinforcement after an unpredictable number of responses that averages around a set value. On a VR-10 schedule, the reward comes after about ten responses on average, but any single reward might follow 2 responses or 25. Because the next response could always pay off, the organism responds at a high, steady rate with little pausing. This schedule is typically the most resistant to extinction, because a long run of unrewarded responses looks like normal variation rather than a sign that reinforcement has stopped.

On the MCAT: A passage describes gambling, a rat pressing a lever, or a salesperson making calls, and asks you to name the schedule. You may also have to predict which schedule gives the highest response rate or the slowest extinction. In cumulative-response graphs, VR appears as a steep, smooth line. Fixed ratio is steep with short flat pauses after each reward, fixed interval is scalloped, and variable interval is a moderate, steady slope.

Common confusion: Students mix up variable ratio with variable interval. Ratio schedules count responses, so responding faster earns rewards faster. Interval schedules depend on elapsed time, so extra responding adds little. Also, VR is a reinforcement schedule, not a type of punishment or negative reinforcement.