A weight-loss company wants to test whether its weight-loss program works. They identify 30 new members, who agree to attend weekly meetings and weigh in at the meetings. They also pay 30 nonmembers to weigh in once a week with the understanding that they will avoid the company’s weight-loss meetings. After 3 months, a greater proportion of the 30 members lose weight than the nonmembers. The company advertises that its program works.
a. Describe the problems with the weight-loss study. Include in your description at least one possible lurking or confounding variable and identify which type it is.
b. Redesign the study so that it is a well-designed experiment.