A large group of hyperactive children whose regular diets included foo

(A) Proportionate comparison is incorrect.
(B) True, the entire population was studied a control group was not taken as such we can not be certain about the results/observations.
(C) Number of children is not the concern here.
(D) Out of scope.
(E) Frequency of Behaviour problem - Not discussed, hence out of context.

Correct Answer must be (B)

This question reminds me of every argument that I have with my boss regarding the effectiveness of a campaign or strategy by looking at absolute numbers & not considering a control group :D

(A) there is no evidence that the reduction in behavior problems was proportionate to the reduction in food-additive intake ----- We just need an answer in yes/no terms whether the reduction in behavior problems was caused by reduction in food-additive intake and do no need to know the degree of reduction. Hence out of scope.

(B) there is no way to know what changes would have occurred without the change of diet, since only children who changed to a low-additive diet were studied ----- Correct. It may be possible that a reduction in behavior problems was observed in even in children who still continued the same diet. to arrive at the the desired conclusion, we need to rule out this possibility.

(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 ----- We do not need a precise number as we already have the percentage of the children in question

(D) there is no evidence that the behavior of some of the children was unaffected by additives ----Out of scope. We just need to establish that a low-additives diet leads to a reduction in behavior problems in children

(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---- No such claims have been made in the data.

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 placed on a low-additive diet for several weeks, after which they were observed 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 cited 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 - WRONG. 'Proportionality' ruins this option. Otherwise it was good.

(B) there is no way to know what changes would have occurred without the change of diet, since only children who changed to a low-additive diet were studied - CORRECT. Not 100% sure how this is right but it is. Hopefully the large group remained unchanged so this option confuses. Alternate cause is what i was looking for but none of the options offer that.

(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 - WRONG. Knowing the number would not have helped us anyhow.

(D) there is no evidence that the behavior of some of the children was unaffected by additives - WRONG. Yes, that's what passage also suggests. So nothing wrong as such in that.

(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 - WRONG. If it's consistent then how can it be flawed.

Answer A.

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