Hannah wants to see if her new technique of ping-pong playing can decrease the time it takes to finish a ping-pong game. She asks the U. S. Olympic ping-pong team to work with her. Half of the U. S Olympic team is randomly assigned to be taught by the new style, the experimental group, and the other randomly assigned half are not, the control group. Her technique does not significantly decrease the time it takes the experimental group to finish a ping-pong game compared to the control group, perhaps because they are already so good at the sport. This could be an example of: