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Author Topic: Logic Problem Question Help  (Read 514 times)


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Logic Problem Question Help
« on: March 15, 2012, 06:25:45 PM »

This is my first post here, and in fact I just decided I wanted to go to law school a week ago so I am still a little new to all of this. As such, I am going through my first book of practice tests (10 Actual, Official LSAT Preptests from the LSAC) and in the first section of logic problems I found one that I did not understand. Overall, I missed 4 of them and understand where I went wrong in 3, but this one I decided I need more help with.
Thanks for your time, and again as a newbie let me know if I am breaking any taboo's by posting a problem on the board or anything else. Here's the problem:

A large group of hyperactive children whose regular diets included food containing large amounts of additives was observed by researchers trained to assess the presence or absence of behavior problems. The children were then places on a low-additive diet for several weeks, after which they were observes again. Originally nearly 60 percent of the children exhibited behavior problems; after the change in diet, only 30 percent did so. On the basis of these data, it can be concluded that food additives can contribute to behavior problems in hyperactive children.

The evidence above fails to establish the conclusion because

(A) there is no evidence that the reduction in behavior problems was proportionate to the reduction in food-additive intake

(B) there is no way to know what changes would have occurred without the change of diet, since only children who change to a low-additive diet were studied

(C) exactly how many children exhibited behavior problems after the change in diet cannot be determined, since the size of the group studied is not precisely given

(D) there is no evidence that the behavior of some of the children was unaffected by additives

(E) the evidence is consistent with the claim that some children exhibit more frequent behavior problems after being on the low-additive diet than they had exhibited when first observed

Right answer: B

Ok, so when I first read the answers I didn't like any of them. I understand that A is wrong because because that's the only evidence provided, D is wrong because it's irrelevant to the question, and E is wrong because it confuses the claim. I didn't like B or C but I ended up picking C because I didn't think one would need a control group for this experiment. Wasn't picking "a large group of hyperactive children whose regular diet included food containing large amounts of additives" in the first place a solution to not having a control group? We already know what the result would be if the children's diet remains unchanged: they would be hyperactive and 60 percent would exhibit behavior problems. So what's wrong with giving them ALL the diet???

Again, I don't like C much either as it misses the point, but I had to choose an answer and theoretically if only 3 children were studied it would be a poor experiment. Should I have gotten the right answer by eliminating the obvious wrong ones, including C?
Please help with the logic of this question, thanks!



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Re: Logic Problem Question Help
« Reply #1 on: March 31, 2012, 10:04:22 PM »
I'm new to the LSAT as well,  I'll try my best to give my take on the question. When I read the question (B) jumped out because it's necessary for the conclusion to be true. The study did not compare any children not on the diet to see if their behavior changed. That's significant because if there was a change without the diet then the findings wouldn't support the conclusion. Furthermore, it attempts to make a generalization about the whole population of hyperactive children, based on a small unrepresentative sample.