Interesting question.
bhatiasanjay01 wrote:
A recent study of college students shows that, contrary to predicted results, special nutritional planning does not positively affect students’ grades. Sixty students, half of whom were given a nutritionally balanced diet, had grades no higher than did those students who were not placed on the diet plan.
In blue, I've highlighted the conclusion that is drawn. Is this conclusion part of the study? We don't know. In any case, it's a strange conclusion: from a study of only college students, the writer concludes that nutrition "does not positively affect students’ grades" in general. If you wanted to weaken the conclusion, answer D is a clear choice:
bhatiasanjay01 wrote:
iv) High school students who previously had low grades found that after they altered their diets, their grades improved dramatically.
But weakening the conclusion is
not what we're asked to do. The question is:
bhatiasanjay01 wrote:
Which of the following, if true, is most useful in determining the accuracy of the study described above?
I highlighted the part of the stem that refers to the study in red. We're asked to assess the accuracy of the study itself, not the conclusion. We can ignore what I've highlighted in blue. The only answer that refers to the methodology of the study (research methods, population that was studied, etc), is E:
bhatiasanjay01 wrote:
v) All of the college students who volunteered for the study were either in their first or second year of college.
Those studied were volunteers- the sample isn't random- and they were from a particular subset of the overall population. This could affect the vailidity of the study; a properly conducted study might reveal different results. So I agree with gixxer here; the correct answer should be E.