Jamie is reviewing a new diet plan that involves purchasing pre-packaged meals and taking a patented energy supplement. In an ad explaining how it works, Jamie reads about a study cited as evidence supporting the effectiveness of the plan. In the study, two groups were followed: one following the plan and another following a simple low-carbohydrate diet. What should Jamie look for in the study to have full confidence in its scientific reliability?

Question

blues · Answer

Were the people in the two groups randomly selected? If all the people in one group were overweight, inactive diabetic smokers while all the people in the other group were incredibly fit elite distance runners, then of course the difference between the groups would not be due to the difference between the diets.

Were all other factors kept the same? If one group was put on an exercise program with personal physical trainers and dieticians to help them and the other group wasn't, then you wouldn't be able to tell what difference between the groups is due to the diet and what difference is due to the other treatments.