In the previous post, we saw how Critical Reasoning questions on the GMAT^® are based on rules of formal logic. We took the specific case of the arguments that incorrectly assume that correlation implies causation.

Just to summarize, X and Y are correlated does not mean X is causing Y since

1. there is no evidence to prove that the direction of causation is from X to Y, it can also be from Y to X
2. there can be a different reason, Z, for the occurrence of Y.

So based on arguments that conclude that X is causing Y since X and Y are correlated, there can be three types of questions that can be asked — Weaken, Assumption and Strengthen.

Weaken Type: Correct Option will always show that in fact Y is causing X (third cause Z is usually not given in the options since it will make the answer two obvious)

Researchers have concluded from a survey of people aged 65 that emotional well-being in adulthood is closely related to intimacy with siblings earlier in life. Those surveyed who had never had any siblings or who said that at college age they were emotionally distant from their siblings were emotionally less well adjusted at 65 than were those who had been close to at least one brother or sister.

Which of the following, if true, most seriously weakens the researchers’ argument?

(A) As they get older, many people think more about their mortality and thus must confront feelings of loneliness and isolation.
(B) People suffering from the emotional distress of maladjustment usually remember being less intimate with other people than they actually were.
(C) Memory of one’s past plays a greater role in the emotional well-being of older people than it does in that of younger people.
(D) Siblings are more likely to have major arguments and deep differences of opinion at college age than at any other time of their lives.
(E) Few people can correctly identify the true sources of their emotional well-being or of their emotional difficulties.

In this particular study, researchers have found that intimacy with siblings earlier in life (X) is closely related (correlated) with emotional adjustment later in life (Y). How did the researchers arrive at this conclusion?

The participants in survey would have been asked two questions:

1. Were you close to your siblings when you were young?
2. Are you emotionally happy and adjusted now?

They would have found that most of the people who answered NO to question A also answered NO to question B. Based on this they concluded that X is causing Y. The correct option will have to point out that Y is causing X.

Option B does exactly that, people who have answered NO to the question B are likely to answer NO to question A even if in reality the answer was YES; since they are currently maladjusted they tend to remember their past relationships in a negative light.

In all Weaken type questions based on correlation-causation arguments (typically such CR passages will mention some sort of study or research), the correct option will always show reverse causation.

So, all one needs to do is identify the option that shows the same; the rest of the options can be eliminated straightaway.

In the next post we will look at Assumption and Strengthen questions based on correlation-causation passages.