A year ago the government reduced the highway speed limit, and in the year since, there have been significantly fewer highway fatalities than there were in the previous year. Therefore, speed limit reduction can reduce traffic fatalities.

The argument is most vulnerable to the criticism that it takes for granted that

This is telling us that the argument is taking something for granted (assuming something to be true) and we need to figure out what the argument is assuming.

Boil it down-The argument is flawed in that it mistakes a correlation between two events for a causal one. The argument took for granted that something else did not cause the reduction in the number of traffic fatalities.

(A) highway traffic has not increased over the past year. -Incorrect; states the opposite of what it should. Increasing highway traffic would increase the risk of traffic accidents.

(B) the majority of drivers obeyed the new speed limit. -Incorrect; need not be true. The reduced highway speed limit could have reduced highway fatalities even if only some people had obeyed the new speed limit.

(C) there is a relation between driving speed and the number of automobile accidents.- Incorrect; Why do we need to assume any connection between the speed limit and the number of accidents? Couldn't it be the case that the reduced highway speed doesn't reduce the number of accidents, but it does reduce the severity of those accidents so that more people survive them.

(D) the new speed limit was more strictly enforced than the old. - Incorrect; The new speed limit could have been equally enforced as the old speed limit and yet the new speed limit could still have reduced the number of highway traffic fatalities.

(E) the number of traffic fatalities the year before the new speed limit was introduced was not abnormally high. - Correct; eliminates a possible alternative explanation for why there was a reduction in the number of highway traffic fatalities.

Answer E

A nice analogy to illustrate option E(found in

MGMAT forum)-

One night, Kobe Bryant scored 81 points in a basketball game (though his average is about 30 points per game). If he scored 30 points the following night, we could say that he scored fewer points than he did the previous game.

Say he wore a new pair of shoes for the 30 point game. Would we say, "Ah, clearly wearing a new pair of shoes can decrease how many points Kobe scores"?

We could, but we could also just say "the new shoes didn't do anything wrong. This is an average, normal game. It's the 81 point game that needs an explanation. THIS game doesn't need one."

That's the way that (E) is hurting the argument. You wouldn't give new speed limits "causal credit" if the fatality number came back to average.

(In statistics, this is called a natural "regression to the mean")

After an outlier data point, you're going to naturally see subsequent data points that are closer to the average. This drift doesn't need an explanation beyond the law of averages.

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