Variable Ratio Schedule (VR)
This is going to be a little confusing at first, but hang on and it will become clear. A variable ratio schedule (VR) is a type of operant conditioning reinforcement schedule in which reinforcement is given after an unpredictable (variable) number of responses are made by the organism. This is almost identical to a Fixed-Ratio Schedule but the reinforcements are given on a variable or changing schedule. Although the schedule changes, there is a pattern - reinforcement is given every "N"th response, where N is the average number of operant responses. Let's give an example. You conduct a study in which a rat is put on a VR 10 schedule (the operant response is pressing a lever). This means that the rat will get reinforced when it presses the lever, on average (and this "on average) is the key), every 10 times. However, because it is an average, the rat may have to press the lever 55 times one trial, then only 2 times the next, 30 the next 50 the next, 1 time the next, and so on....just as long as it all averages out to reinforcement being delivered every 10 lever presses. See, it wasn't that bad.