Since muscle tension in the head region has been associated with tension headaches, you reason that if muscle tension could be reduced, perhaps the headaches would decrease or go away altogether.You design an experiment in which nine subjects with tension headaches participate.The subjects keep daily logs of the number of headaches they experience during a 2-week baseline period.Then you train them to lower their muscle tension in the head region, using a biofeedback device.For this experiment, the biofeedback devise is connected to the frontalis muscle (a muscle in the forehead region).The device tells the subject the amount of tension in the muscle to which it is attached (in this case, frontalis) and helps them achieve low tension levels.After 6 weeks of training, during which the subjects have become successful at maintaining low frontalis muscle tension, they again keep a 2-week log of the number of headaches experienced.The following are the number of headaches recorded during each 2-week period.

Subject ID Baseline Number of Number of Headaches after Headaches Training 17 13 6 LA