In the previous post, we took up an Assumption Question for discussion. The objective was to try to correctly apply The Negation Method to a tough question and eliminate the trap options; so let’s dive in.

Exposure to certain chemicals commonly used in elementary schools as cleaners or pesticides causes allergic reactions in some children. Elementary school nurses in Renston report that the proportion of school children sent to them for treatment of allergic reaction to those chemicals has increased significantly over the past ten years. Therefore, either Renston’s schoolchildren have been exposed to greater quantities of the chemicals or they are more sensitive to them than schoolchildren were ten years ago.

Which of the following is an assumption on which the argument depends?

(A) The number of school nurses employed by Renston’s elementary schools has not decreased over the past ten years.
(B) Children who are allergic reaction to the chemicals are no more likely than other children to have allergies to other substances.
(C) Children who have allergic reactions to the chemicals are not more likely to be sent to a school nurse now than they were ten years ago.
(D) The chemicals are not commonly used as cleaners or pesticides in houses and apartment building in Renston.
(E) Children attending elementary school do not make up a larger proportion of Renston’s population now than they did ten years ago.

Step 1: The first step in any CR question is to identify the argument. Every CR passage (except the conclusion question type) uses premises (facts, findings, beliefs) to put forward an argument. So, the first task is to separate the premises from the argument, which is also referred to as contention,conclusion, assertion, claim, suggestion or plan of action. Let us do the split for the above passage.

Premise 1: Exposure to certain chemicals commonly used in elementary schools as cleaners or pesticides causes allergic reactions in some children.

Premise 2: Elementary school nurses in Renston report that the proportion of school children sent to them for treatment of allergic reaction to those chemicals has increased significantly over the past ten years.

Argument: Therefore, either Renston’s schoolchildren have been exposed to greater quantities of the chemicals or they are more sensitive to them than schoolchildren were ten years ago.

The split need not always be in the sequence of the sentences as they are in the passage(like in the above question). The argument can also be presented right at the beginning of the passage and followed up with supporting premises.

The argument draws only two possible outcomes from the premises:

Either Renston’s schoolchildren have been exposed to greater quantities of the chemicals
Or
They are more sensitive to them than schoolchildren were ten years ago

The question is asking you to identify the assumption based on which this specific conclusion has been drawn. The Negation Method states that if you negate or falsify the assumption then the conclusion should immediately collapse. If you negate an option and that does not lead to the conclusion collapsing then that is not the assumption on which the conclusion is based.

The close options in this question are C & E. Let us negate these options one by one starting with E.

Option (E): Children attending elementary school DO NOT make up a larger proportion of Renston’s population now than they did ten years ago.
Negation (E): Children attending elementary school DO make up a larger proportion of Renston’s population now than they did ten years ago.

Effect on Conclusion: So children attending elementary school make up a larger proportion of the population now. So that does that mean that the reasons concluded — more exposure or more sensitivity — cannot be the reasons? No, this will still hold because the premise says that the proportion of elementary students suffering from allergies has increased. If there are are more children in the age group that does not mean that proportion of allergic-reaction cases should increase.

For example, if the earlier proportion was 2 out 10 and the number of children increased by 10, then among the 10 new children those suffering from allergies would be 2 and the proportion should still be the same at 4 out of 20, which is nothing but 2 out of 10. If as the premise says, the proportion has increased it has to be because of the reasons mentioned in the argument.

So the assumption is not that the number of children has not increased.

Option (C): Children who have allergic reactions to the chemicals ARE NOT MORE LIKELY to be sent to a school nurse now than they were ten years ago.
Negation (C): Children who have allergic reactions to the chemicals ARE MORE LIKELY to be sent to a school nurse now than they were ten years ago.

Effect on Conclusion: This means that compared to ten years ago more students are now being tested for allergies. Thus the reason for the proportion of increase in allergies cannot only be more exposure or more sensitivity, it can be due more students being tested specifically for the same. The argument has assumed that more testing is not the case. So if C is negated then the conclusion fails and hence this has to be the answer.

A good analogy to this understand question would be look at the same type of an argument and answer options in a different context.

Premise: The proportion of women in business schools has increased over the past ten years.
Argument: Either business schools have decided to consciously decided to select more women to promote gender diversity or women have become more capable to meet the requirements for admission into top business schools.

Equivalent Option of (E): The proportion of people in the population who apply to business school has not increased.
Equivalent Option of (C): Women aspiring to a career in management are not more likely now to apply to business schools than they were ten years go.

The question is quite a tricky one and it might have happened that might have debated between (E) and (C) and correctly chosen option (C) based on gut-feel.

But to consistently get 8 out of 10 CR questions right, test-takers would need to move from a gut-feel based approach to a strategy-based approach to eliminate answer options.

Feel free to posts your doubts in the comments section regarding the discussion on the options C & E or any of the other options you felt were close.