moulayabdesslam wrote:
Half of the subjects in an experiment--the experimental group--consumed large quantities of a popular artificial sweetener. Afterward, this group showed lower cognitive abilities than did the other half of the subjects--the control group--who did not consume the sweetener. The detrimental effects were attributed to an amino acid that is one of the sweetener’s principal constituents.
Which of the following, if true, would best support the conclusion that some ingredient of the sweetener was responsible for the experimental results?
A. Most consumers of the sweetener do not consume as much of it as the experimental group members did.
B. The amino acid referred to in the conclusion is a component of all proteins, some of which must be consumed for adequate nutrition.
C. The quantity of the sweetener consumed by individuals in the experimental group is considered safe by federal food regulators.
D. The two groups of subjects were evenly matched with regard to cognitive abilities prior to the experiment.
E. A second experiment in which subjects consumed large quantities of the sweetener lacked a control group of subjects who were not given the sweetener.
This is a good CR question from GMATPrep.
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Need Kudos
Dear
moulayabdesslam,
This is a great question! I'm happy to help.
For this and related question, it's good to have the general ideas of experimental design. See:
Medical Trials and the Placebo Effect on the GMAT Critical ReasoningA.
Most consumers of the sweetener do not consume as much of it as the experimental group members did.The conclusion concerned the comparison of control group to experimental group. What people do in the outside world is not directly relevant to the conclusions based on this within-experiment comparison. This is not correct.
B.
The amino acid referred to in the conclusion is a component of all proteins, some of which must be consumed for adequate nutrition.That's fascinating but it doesn't help us at all in deciding whether this amino acid or anything else in the sweetener played a role in making the experimental group show lower cognitive abilities. This is not correct
C.
The quantity of the sweetener consumed by individuals in the experimental group is considered safe by federal food regulators.Well, that's certainly good: for legal and ethical reasons, we would hope that this is true, but other than keeping people alive, this plays no role in determining what caused the difference in abilities. This is not correct
D.
The two groups of subjects were evenly matched with regard to cognitive abilities prior to the experiment.Aha! This is interesting! Suppose this weren't true! For the sake of argument, suppose the challenge were mathematical in nature. Suppose the control group were a bunch of people with Ph.D.s in mathematics and experimental group were folks who could not get past Algebra One in school. Clearly, these two groups have differing mathematical abilities! If they perform differently on a math task, that's hardly a surprise, and probably not due to the sweetener or whatever is in it! If the two groups have different abilities, then that introduces a plausible alternative explanation for the differing performances in cognitive abilities. A good experimental design would guarantee that the folks in the two groups were evenly matched in cognitive skills, so that there was no pronounced difference in either direction, so that the result can only be attributable to the sweetener and nothing but the sweetener. This extraordinarily strengthens the conclusion!
E.
A second experiment in which subjects consumed large quantities of the sweetener lacked a control group of subjects who were not given the sweetener.The second experiment sounds poorly designed, and tells us nothing about the conclusion in the first experiment. This is incorrect.
The only possible answer is
(D).
Let me know if you have any questions.
Mike