Question

A group of individuals were selected to participate in a diet program. Waist circumferences were collected before and after the program. The question of interest was whether there was a mean change in circumference due to the diet program. The researcher found a mean change of 2.2 inches and wants to conclude that the diet works. Can the researcher make this conclusion? Why or why not?

Answer 1

No the researcher can not make such a conclusion based on change in mean only.

It might be possible that the change is due to huge increase in few individuals. Therefore, variability of the change must be taken into account. Another concern is that whether the change of 2.2 inches is significant or not. A change may not be significant and requires significance testing to identify a significant change. Here the same group is followed in two occasions and hence a paired sample test (e.g. paired t test) is appropriate for the purpose. Followed by ghe findings of the relevant hypothesis test, the conclusion can be made.