You want to compare two methods for weight reduction. You recruit 123 people who are interested in losing weight. You instruct everyone to use the first method until they have lost 10 pounds and then use the second method until they have lost 10 more. You then compare the length of time it takes to lose the first 10 pounds to the length of time it takes to lose the next 10 pounds.
Discuss the potential problem of the following study and propose an alternative way to prevent the problem.