A recent study of college students shows that, contrary to predicted

Interesting question.



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:



But weakening the conclusion is not what we're asked to do. The question is:



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:



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.

Wait... So the fight is so hot b/w D and E. Let us analyze the weak points and strength points of each choice in "determining the accuracy of the study described above":

E: What makes this choice suitable is the fact that it points at some weaknesses in the methodology. Right. So let's put this choice aside for now since it may be the best choice. So, this choice helps us evaluate the accuracy of the study by evaluating the methodology. The methodology in part determines the accuracy of a study.

D:
The problem with E is that since it talks about a test result that was drawn about HIGHSCHOOLS students, it may be considered IRRELEVANT. BUT, on it's good side, choice E states a result from another study-no matter with what kind of subject/sample, that directly stands AGAINST that of the main study. Right? IanStewart, you are right that choice E is an obvious weakener to the conclusion, but what's wrong with it? This fact can not prevent this choice from "determining the accuracy of the study described above"? Not only it's not prevented but also weakening the results, and determining the accuracy of the results of a study are two concepts so close to each other. If we can weaken a conclusion, the perceived accuracy will be decreased.

The golden point is this: Look at the stem again; it says: A recent study of college students shows that, contrary to predicted results, special nutritional planning does not positively affect STUDENT'S grades. The counterargument (what we are to determine the accuracy of the results of a study against it) is about students' performance in general, NOT just performance of COLLEGE students. So a hypothesis about any kind of STUDENTS' performance can be tested by studying ANY KIND of students.

In sum, my choice is D. Though both D and E aim at accuracy of the conclusion, while E focuses on the defects of methodology, D focuses on the DIRECT opposite results found from another VALID study. Do not forget the point: we are talking about a conclusion about ALL students.

What is the source of this question?

Actually, there is no ambiguity in the question.

What was the study? 60 students were put on nutritious diet. 60 were not.
What was the result? The 60 students who were put on nutritious diet did not have higher grades than other 60.
What did they conclude? Special nutritional planning does not positively affect students’ grades.

Now, we need to evaluate the accuracy of the study. What will help us figure out whether what we concluded from the study is valid or not?
Because 60 students with diet plans did not get better grades, can we say nutrition does not have any positive affect on grades? Perhaps not. What if nutrition can improve low grades (by giving students more energy and making them more active) and bring them up to average (but not improve average to take them to above average since they need to work hard too)? If this were true, the conclusion of the study would not be valid. Special nutritional planning WOULD have a positive affect on students’ grades. "If grades were low, they could become better by nutritional planning"
Hence option (D) is useful in determining the accuracy of the study.

As for other options, focus on what was concluded from the study. Are they relevant to the conclusion "Special nutritional planning does not positively affect students’ grades."?

(A) Performance of business executives was shown to improve drastically after major alterations were made in their diets.
Not relevant to students' grades.

(B) Honors students, after altering their diets, maintained that they did not change their study habits.
Students saying that they did not alter their diet doesn't mean anything. It is true that they said it but did they actually maintain their study habit or not, we don't know. So not relevant. No need to think further.

(C) Students who participated in various fitness regimens found that their grades improved appreciably after they altered their exercise habits.
Nothing to do with fitness regime and grades. Only food and grades connection is our concern.

(E) All of the college students who volunteered for the study were either in their first or second year of college.
Again, not relevant.

We need to find the option that is MOST helpful in determining the accuracy of the study.

The study says "special nutritional planning does not positively affect students’ grades"

(D) says "High school students who previously had low grades found that after they altered their diets, their grades improved dramatically."

This is directly against the result of the study. It implies that the study is not accurate.

Option (B) talks about honors students. We do not know how many students in the study were honors students. So we don't know how relevant this information is to our study.

Hence answer is (D) only.

(E) only tells you that they are 1st or 2nd year students, not 3rd or 4th year. How does that affect your study? Half of them are getting balanced diet and half are not. Even if they were 3rd and 4th year students, why would we challenge the results of the study?

Part of what makes this an unfair question is the phrasing of the sentence "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." Is it saying that there was a group of 60 students who all volunteered for the study, half of the volunteers received a nutritious diet, but all 60 (regardless of diet) had higher grades than students who weren't involved in the study? Or is it saying that of the 60 students who volunteered for the study, the half who were given a nutritious diet had the same grades as the half who didn't?

Even though the first reading seems illogical, it's what the sentence is saying, grammatically! But if the second reading is what's intended, I can understand why (E) isn't correct. If every student who volunteered for the study was in the first or second year, including both the students who were given a nutritious diet and the students who weren't, then the result could still be valid. It's not extensible to the entire college population (maybe, for some weird reason, nutrition only affects older students and not younger ones?) but it's still valid, because it's comparing two comparable groups.

(D) is certainly wrong by GMAT standards too, though. The GMAT doesn't accept answers that require that you assume that one group of people is the same as another group of people, without proving it. The argument would have to show that high school students are physiologically the same as college students, for (D) to stand a chance.

Usual disclaimer applies here: even the best test-prep companies really struggle to perfectly copy the style of the actual GMAT. And that's particularly true on CR and RC.

This one, in my opinion, is particularly off. Has anybody ever seen an official GMAT question phrased this way?



More importantly: what does that even mean?! Accuracy of the study's conclusions? How carefully the study was conducted? The question itself makes very little sense -- and I have no idea how you would even begin to answer it.

So for anybody worrying about this one: please move on, and use the tags to find discussions of better questions.

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.

Which of the following, if true, is most useful in determining the accuracy of the study described above?

In order to determine the accuracy of the study, we need some information which either bolsters or undermines the argument made by the study. We, also,
have to stick to the same/similar sample space.

A) Performance of business executives was shown to improve drastically after major alterations were made in their diets.

The sample space changes from Students to Executives.

B) Honors students, after altering their diets, maintained that they did not change their study habits.

If we chose this option, it will convey that we are extrapolating the study habits of honors students to improved marks.

C) Students who participated in various fitness regimens found that their grades improved appreciably after they altered their exercise habits.

But here we are talking about diets. This option compromises the setting of the study.

D) High school students who previously had low grades found that after they altered their diets, their grades improved dramatically.

This option presents an information which establishes a positive correlation between diet and grades. This shows that the study is not accurate. Maybe the students those were given nutritionally balanced diet previously scored very poor marks as compared to the other half.

E) All of the college students who volunteered for the study were either in their first or second year of college.

So what?

Thus, option D.

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.

Which of the following, if true, is most useful in determining the accuracy of the study described above?

In order to determine the accuracy of the study, we need some information which either bolsters or undermines the argument made by the study. We, also,
have to stick to the same/similar sample space.

A) Performance of business executives was shown to improve drastically after major alterations were made in their diets.

The sample space changes from Students to Executives.

B) Honors students, after altering their diets, maintained that they did not change their study habits.

If we chose this option, it will convey that we are extrapolating the study habits of honors students to improved marks.

C) Students who participated in various fitness regimens found that their grades improved appreciably after they altered their exercise habits.

But here we are talking about diets. This option compromises the setting of the study.

D) High school students who previously had low grades found that after they altered their diets, their grades improved dramatically.

This option presents a piece of information which establishes a positive correlation between diet and grades. This shows that the study is not accurate. Maybe the students those were given a nutritionally balanced diet previously scored very poor marks as compared to the other half.

E) All of the college students who volunteered for the study were either in their first or second year of college.

So what?

Thus, option D.

Evaluate the conclusion : special nutritional planning does not positively affect students’ grades.

B (close contender): Honors students, top of the class, didn't vary their study practice. If true, it doesn't prove any 'positive result' from nutrition as there simply might not be any room left for improvement amongst these brilliant subjects. If false, that doesn't negate the conclusion either as we simply don't know whether they changed their study habits for good or for worse.

D (winner): Got a Benchmark to compare against. Low grades improved to high grades after altering diets. If true, then the conclusion is negated. If false, then conclusion is reinforced. Only hitch I found is - argument talks about 'college students', but this option talks about a different sample : 'high-school students'. But, finally conclusion is bothered about the link between Nutritional Change -> Grades, not source of the sample.

Hello from the GMAT Club VerbalBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.