PrepTest 131

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
A high school modified it's AC, resulting in decreased humidity. The next day, many more kids went to the nurse. Therefore, decreased humidity can cause illness.

Answer Anticipation:
The conclusion of this argument is causal ("can make"), so your first thought in considering the gap in the logic of this argument is a jump from correlation to causation.

Interestingly, there is a causal premise—the modified AC "caused" the humidity to decrease. However, that's not a causal relationship that establishes the conclusion—rather, it sets the background for the school's humidity having decreased. The premises related to the conclusion—the relationship between humidity and illness—is a correlation. The humidity went down, and visits to the school nurse went up the next day. Since that correlation serves as the basis for the causal conclusion, this argument does commit a correlation/causation flaw.

Thinking this through also highlights another gap in this argument—the premise is about visits to the school nurse, but the conclusion is about illness. This argument is using school nurse visits as a way to measure illness, but it's possible that students were visiting the nurse for other reasons (maybe it was the week where everyone was getting a hearing screening, or there was a test and people were faking!).

In both cases, the argument is relying on alternative causes not being present—the argument relies on illness driving students to the school nurse, not something else.

Answer Explanation:
This answer rules out the possibility that the visits to the nurse were caused by something other than illness. If all of those visits were not due to illness, then the argument falls apart—if illness didn't drive the nurse visits, then there's no basis to conclude that a decrease in humidity causes illness.

Key Takeaway:
In Strengthen questions with correlation/causation flaws, the correct answer will generally: eliminate an alternative cause; bring up more examples of cause and effect going together; bring up a control, where there's no cause and no effect. For Strengthen with Necessary Premise questions, the correct answer tends to be more about ruling out alternatives than the other two categories of answer.

Incorrect. The argument doesn't require most of the students to suffer from the decrease in humidity, just that enough did to account for the 25% increase in visits to the school nurse. (Note that it doesn't even require 25% of the students to have suffered. The stimulus states that visits increased 25%, which could have been only a handful of visits if the average day sees 20 or so visits to the nurse.)

Incorrect. It's unclear what this answer is saying about the argument. Is it presenting viruses as a potential alternative cause? Is it presenting viruses as a means by which the AC/humidity could have led to illness? In any case, this answer is way too specific in detail (24 hours being an exact number) and vague in impact (see initial questions) to be necessary for the argument to work.

Incorrect. There's a subtle shift between the stimulus and this answer. In the stimulus, it states that the number of visits to the school nurse increased by 25%—that means 25% higher than normal, or, say, 20 visits becomes 24. This answer states that someone's chances increased by 25%—so if there's normally a 5% chance that someone would go to the nurse, it's not 30%. That would result in a much larger increase in the number of visits to the nurse! That said, ignoring this math/grammar jump, the answer would still be too specific to be necessary—if the increased probability of becoming ill was 24% or 26%, the argument could hold together.

Incorrect. The argument's conclusion is about decreases in humidity causing illness—the cost cutting was background info that's out of scope of that relationship.