Partial-reinforcement schedules, especially variable ratio and variable interval, cause behavior to be more resistant to extinction. This phenomenon is known as the patrial-reinforcement effect. ex... A rat is in a box, to get a food it must press a level. So food is reinfoser. If a rat is trained to press a level only on continuous reinforcement and then is shifted to extinction conditions, the rat will typically make a feu bursts of level press responses and then quit. But if the rat has been shifted gradually from continuous reinforcement to an ever-stingier variable schedule and then finally to extinction, it will often make hundreds of unreinforced responses before quiting.