Dear Dollysharma
I'm happy to respond. You posted neither the source nor the OA, and I suspicious about this question. It's not crucial for answering the question, but I am wondering about GM --- do they mean "genetically modified"? That would be an odd topic, and that's a non-standard abbreviation.
Here's my analysis:
(A) People who completed the diet and people who discontinued had same level of health before the experiment.
If anything, this would be a strengthener. This is incorrect.

(B) People who followed the GM diet took vitamin supplements for boosting their health during the experiment.
Very promising: if folks following the diet took vitamins, and folks who "[returned] to their old food habits" gave up the vitamins, then the vitamins may well be a better explanation for increased health than would be the diet itself. This is a good weakener.

(C) Once people start following a healthy diet they become cautious about their health.
Hmm. That would mean that everyone initially was cautious about their health, not a clear separator. Would this caution come to an abrupt end when the drop-outs resumed their old "food habits"? Unclear. Finally, does being cautious about health necessarily result in more robust health? Unclear. This is wishy-washy, not a good weakener. This is incorrect.

(D) Before the experiment was conducted, people who could complete the diet plan were relatively healthier than the people who could not.
This is very strange. Something would be eerie, and definitely unscientific, if somehow we could "tell" who would or wouldn't complete the diet before they even began the experiment. That's not sensible. I assume what this means is that the researchers measured everyone's health in great detail, and then after the experiment, they went back and, comparing those who completed with those who dropped out, noticed this pattern. If this is the case, this is another strong weakener.

(E) Adulterated food can adversely affect the health of a person.
Hmm. This seems out in left field. There was no discussion at all of "adulterated" food. Are we equating GM with "genetically modified" and then equating that with "adulterated"? That's a bit of a stretch: some people would agree, but not everyone. Also, if it is true that GM foods are harmful, then why would a diet of them help people? It contradicts the evidence. This is incorrect.

I could see a strong argument for either (B) or (D). With the real GMAT, there would be one clear right answer and four answers on which there would be some non-negotiable error.

This is a poor question, a question with two legitimate choices for answers. Wrestling with questions such as this will do nothing to improve your GMAT CR skills. I don't know the source, but you may well be better off avoiding their questions in the future.

Here's a high quality CR practice question:
http://gmat.magoosh.com/questions/3148

Does all this make sense?
Mike
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Hi Mike

Thanks for your detailed response! I believe GM diet plan refers to General Motors diet plan; however, as you mentioned it's not crucial for answering this question.

In my opinion, option B is not a good weakener because it talks only about people who followed the diet i.e. those who stuck with it till the end. It only gives information about the people who completed the GM diet plan and doesn’t tell us whether people who quit the plan midway took these supplements or not.

It could’ve been a good weakener if the option statement read, “Only people who followed the GM diet took vitamin supplements for boosting their health during the experiment.” But in its present form, I think we can safely rule it out.

D is the clear answer choice here because of the reason stated by you.

Thanks!
Dolly

Dear Dolly,
Hmmm. A General Motors diet plan?? That's very odd. What does a huge car company know about nutrition? I know there's a real American food company "General Mills" --- they are the parent company of Betty Crocker, Yoplait yogurt, Pillsbury, Green Giant vegetables, Old El Paso products, Haagen-Dazs ice cream, Hamburger Helper, Cheerios cereal, Trix candy, etc. etc. Of course, all this is irrelevant for the question, but the real GMAT would not present a real-world company abbreviation in a problem. That'a very un-GMAT-like. A real company might sue if it were mentioned in an official question from which GMAC is making money: the real company would want a share of GMAC's profits. That's why GMAT has to make up all the imaginary names of companies and places (QuickFreeze, Parland, etc.)

Yes, (D) we agree that is a weakener, but I am unconvinced that (B) is not. It really comes down to a core question: are vitamins food? Of course, that's not a clear or easy question, and we easily could imagine doctors & nutritionist & other health professional giving either a enthusiastic "yes" or a vigorous "no" to that question, and either way, having a sophisticated argument to support their answer. To some extent, the answer reflects an entire lifestyle or a worldview. We certainly could imagine any test taker walking into the GMAT already with an implicit answer to that question. I will say that, in my own life, I would give a strong "yes" answer to that question, and this influenced my reading of the question. We are told the folks who quit the diet halfway through "[returned] to their old food habits." If vitamins ARE food, this means those people dropped the new vitamin regimen when they dropped the diet --- they changed all their "food" choices at once. Now, I can't defend with certainty that it's the "right" answer to say that vitamins are, in fact, food, but insofar as this is a conceivable worldview, this worldview makes (B) a very strong weakener as well.

You see, the GMAT is scrupulously careful. It is certainly not enough if a CR question is perfectly clear to the person who wrote it. Folks come to the GMAT will all sorts of worldviews and life experiences and biases, a bewildering diversity, and from the GMAT's perspective, it would unfair if some people get a question incorrect because they were approaching it with different but totally valid worldviews on some set of life-issues. This gets into very subtle issues. It's extremely hard to write a high quality practice GMAT CR question: not only does it have to have one clear right answer and four clearly incorrect answers, but that clarity must remain irrespective of the kind of worldview with which each test taker approaches the problem. A good wrong answer has to one that everyone, with every legitimate worldview, would say, "Oh, I see, that has to be wrong." It's not a clear wrong answer if some people would say, "Wait! What about X? I believe X, and X would make this answer correct as well!" Of course, GMAC does not do personal interviews about why people chose various answers, but they do gigantic statistical studies --- the "experimental questions" --- and if otherwise good test takers are getting a particular question wrong, it doesn't really matter why they are getting it wrong --- if high performing students consistently get a particular question wrong, then there's something flawed in that question, and the GMAT will not use it. GMAC has the tremendous advantage of this vast pool of statistical data. It is extremely hard to design a question from scratch that will incorporate all the wisdom implicit in that vast pool of data.

At Magoosh, we subject all the questions we write to extensive statistical analysis. If high performing students get a question correct in high percentages, and low performing students get the question incorrect much more frequently, then that question is a valid question, a question that distinguishes students of different abilities. If high performing students are getting a particular question incorrect frequently, about as frequently as low performing students do, then the question is simply not a good question. It's funny: sometimes the question looks perfectly good to us, but the data demonstrates clearly that the question is not good. ---- I know Magoosh does this analysis on our questions, and I believe some other good companies, such as MGMAT, do something similar, but I don't know. I know many companies put out test questions with absolutely no statistical analysis of them: the folks at those companies rely purely on their own intuition, and are oblivious to what data might tell them. Often, those questions are far more problematic, and generate far more discussion & back-and-forth debate on GC. They lack the unambiguous clarity of the official questions.

Now, I don't know the source of this question about the diet, and of course, I have no idea how the data for this question might play out over hundreds or thousands of test-takers. I do know that with a good practice GMAT CR question, I am always convinced of the rightness of one answer choice and the wrongness of the other four, but for this question, I am simply not convinced, and that makes me suspect this is a poor question. If I can have a valid rational worldview in my life, and this worldview leads me astray in the question, then it's not a good question.

Some folks thinks it's a relatively easy thing to write high quality GMAT practice questions. It's actually not too hard to write math questions, although even there are some pitfalls, but on the verbal side, it's a bit mind-boggling to consider all the factors that could possibly compromise any particular question. This is why there are so many poor quality Verbal questions out there, and I believe this question is one of them.

Does all this make sense?
Mike
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Hi,

I mark D as the choice. Here is my analysis:
the correct answer must attack its assumption to weaken the given argument.

conclusion : Clearly, the controlled food intake is at least partly responsible for making people healthy.
Evidence : people who successfully completed a 7 days strict GM diet plan and controlled their intake of food were found to be healthier on average than the people who discontinued the diet halfway and return to their old food habits.

since the question is from Cause/Effect category. hence the people who completed 7 days plans found to be healthier while others not. this means they followed diet as a result become healthier than those who did not follow the diet plan. To attack this - pre think a scenario in which other reason than diet plan is responsible or they were already healthier than others.

Which of the following, if true, most seriously undermines the argument?

(A) People who completed the diet and people who discontinued had same level of health before the experiment.
Level is not considered - out of scope
(B) People who followed the GM diet took vitamin supplements for boosting their health during the experiment.
Okay,effect is there because of different factor i.e supplement here .... I am not able to make out how it will relate to the average people who are undergoing the diet plan.

(C) Once people start following a healthy diet they become cautious about their health. -- not valid
(D) Before the experiment was conducted, people who could complete the diet plan were relatively healthier than the people who could not.
This attacks the average of the people who are healthier while undergoing the Diet plan, others who left in between are not. Hence Correct choice.

(E) Adulterated food can adversely affect the health of a person -- out of scope.

Dear GmatDestroyer2013,
My friend, I would just caution you: on a GMAT CR Weakener question, the correct answer often attacks the assumption, but there are many other possibilities for weakeners besides attacking the assumption. See:
http://magoosh.com/gmat/2012/how-to-wea ... reasoning/

Mike
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My answer is B. Got stuck between B and D, but finally chose B.

Also, a big thank you to Mike for the explanations and the bonus question Got that one correct, by the way!

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