Make a list of some of the factors in your life that change from one day to the next. Possible examples include your mood, health, environment, schedule, obligations, successes and failures, and the quality of your social interactions. Now, imagine that you are in a pre-post study examining how your sense of humor is affected by an acupuncture treatment. The pretest is given one afternoon, the treatment is the next morning, and the posttest is in the afternoon following the treatment.

a. Pick two items from your list of the factors that change from one day to the next, and describe how these changing factors could influence your scores in the research study.

b. Explain why the research study cannot conclude that acupuncture causes changes in a person's sense of humor.