You want to compare two techniques for weight reduction. You recruit 123 people who are interested in losing weight. You instruct everyone to employ the first method till they have lost 10 pounds and then employ the second method till they have lost 10 more. You then compare the length of time it takes to lose first 10 pounds to 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.