The fact that people who exercise vigorously are sick less often than average does not prove that vigorous exercise p...

Naz on January 15, 2014

Let's analyze the argument. The conclusion is: the fact that people who exercise vigorously are sick less often than average does not prove that vigorous exercise prevents illness. Why? Because whether one exercises vigorously or not depends in part on one's preexisting state of health. Here the author is referencing the correlation/causation flaw. She states that just because there is a correlation between people who exercise vigorously and being sick less often, that does not necessarily mean that the former caused the latter. It could, in fact, mean that the latter caused the former: whether one exercises vigorously or not depends in part on one's preexisting state of health. Remember there are two ways to weaken a correlation/causation argument concluding that X causes Y. You can say, as in this case, that Y actually caused X, or that Z (a third unrelated factor) caused both X and Y.

This is why answer choice (A) is the correct answer. It, too, has this inverse relationship. Answer choice (A) states that being a habitual reader is not what causes one to be verbally skilled, but rather it is that those who have strong verbal skills read more. Again we have this similar X did not cause Y, but Y, in fact, caused X.

Answer choice (D) does not have this similar inverse relationship. (D) states that taller children often outperforming other children at basketball is not sufficient to prove that height is a decisive advantage in basketball because taller children merely play basketball more often than other children do. For this to have a similar inverse relationship it would have to state: The fact that taller children often outperform other children at basketball does not show that height is a decisive advantage in basketball, rather it is that those children that outperform others at basketball are taller. Do you see our pattern of not X causes Y, but Y causes X? Answer choice (D) throws in a third variable of "taller children playing more often." Thus, we have our second correlation/causation weakening option of Z causes X and Y.

Hope that helped! Please let us know if you have any other questions.

Batman on January 19, 2014

Your explanation is a major league home run!!!! ^^
Thanks a lot!!