For each of the experiments described below, identify any problems and explain how the problems could have been avoided. 

a. A new drug for attention deficit disorder (ADD) is supposed to make affected children more polite. Randomly selected children suffering from ADD are divided into treatment and control groups. The experiment is single-blind. Experimenters evaluate how polite the children are during one-on-one interviews. 

b. Researchers wonder whether drinking coffee before an exam improves performance. Fifty coffee-drinkers are told not to drink coffee in the four hours before an exam, and 50 non-coffee-drinkers are asked to drink at least two cups of coffee in the four hours before an exam. Both groups had the same average performance on the exam. 

c. Researchers wonder if the effects of a rare degenerative disease can be slowed by exercise. They identify six people suffering from the disease and randomly assign three to a treatment group that exercises every day and three to a control group that avoids exercise. After six months, they compare the amounts of degeneration in each group. 

d. A chiropractor performs adjustments on 25 patients with back pain. Afterward, 18 of the patients say they feel better. He concludes that the adjustments are an effective treatment.