A year ago the government reduced the highway speed limit, and

Question

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

(A) highway traffic has not increased over the past year.
(B) the majority of drivers obeyed the new speed limit.
(C) there is a relation between driving speed and the number of automobile accidents.
(D) the new speed limit was more strictly enforced than the old.
(E) the number of traffic fatalities the year before the new speed limit was introduced was not abnormally high.

KarishmaB · Accepted Answer

- A year ago the government reduced the highway speed limit
- There have been significantly fewer highway fatalities than there were in the previous year.

Conclusion - Speed limit reduction can reduce traffic fatalities.

We are looking for an assumption (takes for granted...)

(A) highway traffic has not increased over the past year.

We don't need to assume that. Number of fatalities has gone down. If highway traffic has increased and number of fatalities has gone down, our conclusion makes just a little more sense.

(B) the majority of drivers obeyed the new speed limit.

We don't need majority to obey the speed limit. Our conclusion is "Speed limit reduction can reduce traffic fatalities". Even if the fatalities have been reduced by a small amount, we can say that speed limit reduction can reduce traffic fatalities.

(C) there is a relation between driving speed and the number of automobile accidents.

This brings in a third variable - automobile accidents. We don't need any relation between driving speed and number of accidents. The argument talks about driving speed and number of fatalities. Ignore.

(D) the new speed limit was more strictly enforced than the old.

We don't know how strictly old or new speed limits were enforced. Even if new speed limits were not more strictly enforced, number of fatalities could have gone down.

(E) the number of traffic fatalities the year before the new speed limit was introduced was not abnormally high.

Yes, this is an assumption. Let's negate it. If the number of traffic fatalities in the year before were abnormally high (higher than normal), the reduction could have just been re-adjustment. It needn't be the effect of lower speed limit. 
2015 - 98 fatalities
2016 - 100 fatalities
2017 - 300 fatalities (abnormally high due to any reason) 
Decreased speed limit ->
2018 - 102 fatalities

Can we say that decreased speed limit caused it? No.

Answer (E)

Skywalker18 · Answer

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.

solikon · Answer

Straight B.

If a majority of drivers refuse to obey new limitations and despite this fact, fatalities decreased it is clear that something else caused fatalities to decrease and therefore make an argument "flawed"

AKY13 · Answer

IMO E
If for whatever reasons(say hug influx of tourists & hence traffic) the accident rate was high, the rate may have decreased without any intervention after the original situation(tourists gone back) may have resumed.

arpitkansal · Answer

nightblade354  can you shed some light on this CR question?

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nightblade354 · Answer

Quick lesson: When the LSAT asks you what the question took for granted, it is asking for the assumption.  But , there are still ways to get around this question without negating each statement. We are still trying to weaken the argument. 
 
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

(A) highway traffic has not increased over the past year. --  So what if it has? This has no connection to accidents. You would have to assume more people = more accidents. And that, itself, is an accident to avoid.  
(B) the majority of drivers obeyed the new speed limit. --  OK, what if less than half obeyed the new law. Would this destroy the argument? Nope. We have no concrete numbers, so if we say that some adhere to the new speed limit, how does this destroy the argument? This could easily cause the number to go up, stay the same, or go down.  
(C) there is a relation between driving speed and the number of automobile accidents. --  OK, what if that relationship means that speeds going down increases accidents? 
(D) the new speed limit was more strictly enforced than the old. --  What does "more" mean? Does that mean 1 extra ticket a month? Or 1 extra ticket for every driver? 
(E) the number of traffic fatalities the year before the new speed limit was introduced was not abnormally high. --  Bingo bango. If the number was abnormally high (say 100), and then the new speed limit made it 50, who is to say this caused the drop? This is our answer.

redskull1 · Answer

It is basically asking for an assumption.So clear E.

If you negate E we get the accidents were abnormally high.So the reduction could in fact be a natural reduction.hence...

Not B because highway fatalities are actually caused by a very very small proportion of drivers...

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KaranB1 · Answer

what's wrong c? what if I negate this answer choice?

redskull1 · Answer

C is incorrect because it is not a criticism.It can perfectly be derived from the argument with reasonable reasoning.

Posted from my mobile device

KaranB1 · Answer

Awesome explanation.....Thank you!!!

Contropositive · Answer

Quick lesson for posterity:

Here's a rule you're going to love: flaws are necessary assumptions.

When a flaw question asks you what the argument TAKES FOR GRANTED, it is asking for a necessary assumption.

When a flaw question asks you what it FAILS TO CONSIDER, it is asking you for a necessary assumption in a roundabout way. It is asking you what necessary assumption the argument is making that causes it to IGNORE ANOTHER POSSIBILITY.

And if you ever just have a question stem that asks you, "What is the assumption?" or "What does the argument assume?", treat it as a necessary assumption question.

saurabhbajpai · Answer

Question clearly uses the term 'significant decline in fatalities', then why does the base matter? In stats, we can call a significant drop/decline only if there's readable base.

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srik410 · Answer

Nice question. I think the label should be a assumption question and not evaluate argument

A year ago the government reduced the highway speed limit, and

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A year ago the government reduced the highway speed limit, and

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