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#23729
Complete Question Explanation

Flaw in the Reasoning. The correct answer choice is (B)

The stimulus concludes that since a switch from a high-additive to the low-additive diet is accompanied by a large drop in the percent of children displaying behavioral problems from an initial to a final observation, food additives must contribute to behavior problems in children.

The argument is unconvincing because there are far too many factors at play to credit, without further information, food additives as a cause of behavioral problems. Also, since there is no control group, you do not know whether it is possible, for instance, that most children would simply behave better the second time that they encounter a situation such as the study.

Since you are asked why the evidence fails to establish the conclusion, you should focus on the fact that the stimulus contains a causal argument that fails to give enough attention to highly plausible alternative causes.

Answer choice (A): It is true that since the high-additive diets could have differed from each other significantly, the proportional decrease in additives might differ widely. However, the stimulus merely proposes the very general conclusion that food additives contribute to problems, so whether the reduction is proportionate for each specific child is not critical.

Answer choice (B): This is the correct answer choice. Since the study does not include children who did not undergo a dietary change, it is not possible to rule out the alternative cause that children simply naturally behave better the second time in a situation, or behave better for other non-dietary reasons, so the conclusion of the stimulus does not follow.

Answer choice (C): The exact number of children in the study is irrelevant, and it is not a flaw to use proportions in a consistent fashion, so this choice is wrong.

Answer choice (D): If there is no evidence that the behavior of some children is unaffected by the additives, that is only more proof for the stimulus. The test-writers are attempting to catch testers who have difficulty with negations, and you need to read more carefully if you chose this response.

Answer choice (E): While it is true that the evidence is consistent with some of the children experiencing more frequent behavior problems on the low-additive diet, that is not a flaw. The stimulus only offers a general conclusion, so a few deviations do not matter. Furthermore, if the move from 60% behavior problems to 30% behavior problems included new problem-children in the 30%, that might suggest a greater benefit from lowering additive levels for the original 60% of children with behavioral problems, so it is unclear why this response should be taken to illustrate a flaw. This choice is wrong.
 reop6780
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#12103
I understand the answer B points out the flaw in the stimuli that there may be other factors influencing hyperactive children.

Still, I chose C due to percentage described in the stimuli.

Since we do not know whether the size of the group tested varied, I thought the percentage did not mean anything, and therefore the exact number of children tested before and after change in diet should be illustrated.

Doesn't C also points out a flaw in the stimuli?
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 Dave Killoran
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#12127
Hi Hyun,

Let's turn this one around. We know answer choice (C) is wrong, and that therefore it does not describe a flaw in the argument. Why might that be, do you think?

Please let me know your thoughts. Thanks!
 reop6780
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#12148
I made my question sound confusing.
What i was trying to ask was whether the group size of children was fixed so that the number of percentage does not cause any error.
I guess since the stimuli states "the children...after which they were observed...," it is convinced that the same group was tested...?

I should have asked this way..

Thank you!
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 Dave Killoran
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#12155
Yes, the stimulus works on the idea that it is the same group of children. Language such as "Originally nearly 60 percent of the children...; after the change in diet, only 30 percent did so" reinforces that idea. The exact size of that group--500? 1000?--is irrelevant because all they said was that it was "A large group," which means the sampling was big enough to reduce bias.

Thanks!
 tetsuya0129
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#81521
Hi Powerscore Staff,

Thanks for the wonderful explanation.

Following the logic of (B), if a correlation-to-causation argumentation does not involve a control group, then the correlation itself is not reliable since other variables aren't properly insulated.

Would you be so kind to help confirm whether the lesson I learned from this question is logically sound?

Thanks very much.
Leon
 Robert Carroll
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#81558
Leon,

I agree with that! I think there is another good example of this issue in another question. I'll link to it here: https://forum.powerscore.com/lsat/viewtopic.php?t=8681 That's a great example of a question where the answer strengthens the argument by saying, basically, that the control group had no observed effect. That bolsters the case for causation in the stimulus. But it couldn't have bolstered the case for causation if the stimulus hadn't been deficient in that respect. So you're right - failing to include a control group is problematic, and while it might not be the only problem with an argument, it is a problem and it's best for an argument to avoid that problem.

Robert Carroll

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