A recent survey of all auto accident victims in Dole County found that

Question

A recent survey of all auto accident victims in Dole County found that, of the severely injured drivers and front-seat passengers, 80 percent were not wearing seat belts at the time of their accidents. This indicates that, by wearing seat belts, drivers and front-seat passengers can greatly reduce their risk of being severely injured if they are in an auto accident.

The conclusion above is not properly drawn unless which of the following is true?

(A) Of all the drivers and front-seat passengers in the survey, more than 20 percent were wearing seat belts at the time of their accidents.

(B) Considerably more than 20 percent of drivers and front-seat passengers in Dole County always wear seat belts when traveling by car.

(C) More drivers and front-seat passengers in the survey than rear-seat passengers were very severely injured.

(D) More than half of the drivers and front-seat passengers in the survey were not wearing seat belts at the time of their accidents.

(E) Most of the auto accidents reported to police in Dole County do not involve any serious injury.

DmitryFarberMPrep · Accepted Answer

This argument comes to a conclusion about the benefits of seatbelts without providing any data about what happens to people who wear them. Let's look at a similar scenario: Imagine that I perform a study that finds that most people with heart disease are not Dutch. Could I conclude that being Dutch protects against heart disease? No, because most people *without* heart disease aren't Dutch, either! I would have to see some data showing that Dutch people show up more in the general population than they do among heart disease sufferers.

Similarly, if we look at all the people who get in accidents--whether they get injured or not--and we don't see more than 20% wearing their seatbelts, then this data doesn't show that seatbelts are safe. It just shows that not many people wear them. If that's the case, then the conclusion doesn't make much sense--seatbelt wearers appear to be getting injured just as much as everyone else (even more, if they represent *less* than 20% of the group). On the other hand, if the assumption in A is correct, and more than 20% of people who get in accidents have their seatbelts on, then we have to wonder why more of them weren't injured. The conclusion starts to look much better.

I hope that helps!

Technext · Answer

A recent survey of all auto accident victims in Dole County found that, of the severely injured drivers and front-seat passengers, 80 percent were not wearing seat belts at the time of their accidents. This indicates that, by wearing seat belts, drivers and front-seat passengers can greatly reduce their risk of being severely injured if they are in an auto accident.

The conclusion above is not properly drawn unless which of the following is true?

Explanation :
--------------------
( A ) Of all the drivers and front-seat passengers in the survey, more than 20 percent were wearing seat belts at the time of their accidents. ---> We know from the excerpt that
 Drivers + Front-Seat Passengers = Severely Injured (20% Wearing Seat-Belts + 80% Not Wearing Seat-Belts) + Not Severely Injured (No Information)

Now, what if more than 80% of the drivers and front-seat passengers who were NOT severely injured were NOT wearing seat-belts? Using this scenario, we can say that wearing seat-belts will NOT reduce the risk of being severely injured. So the conclusion cannot be properly drawn.

Since we have to show that author's conclusion was properly drawn, we have to show that the scenario I cited above was not possible . To make the above scenario impossible, we can say that more than 80% (actually it should be 100% otherwise these people will come under the category of ‘severely injured’ ones) of the drivers and front-seat passengers who were NOT severely injured were  wearing seat-belts . Also, excerpt mentions that 20% people from the severely injured category were wearing seat-belts.

So, if we add people (who were wearing seat-belts) from both the categories (severely injured & not severely injured), we'll arrive at the assumption stated in this option.

( B ) Considerably more than 20 percent of drivers and front-seat passengers in Dole County always wear seat belts when traveling by car. ---> Mentions about car. Irrelevant.

( C ) More drivers and front-seat passengers in the survey than rear-seat passengers were very severely injured. ---> Will not help us in any way to prove that the conclusion was properly drawn.

( D ) More than half of the drivers and front-seat passengers in the survey were not wearing seat belts at the time of their accidents. ---> This cannot be the assumption in order to arrive at the author’s conclusion.

( E ) Most of the auto accidents reported to police in Dole County do not involve any serious injury. ---> Irrelevant.
--------------------

Hope that helps.

Regards,
Technext

priyankurml · Answer

IMO A. I was confused between A and D but finally opted A.

We have to find out why argument believes "wearing seat belts, ... can greatly reduce . risk"? Of course some proof is required to stand this point.
A) see the  blue  part: were wearing - this does validate the claim 
D) were not wearing - this does not validate the claim

pleonasm · Answer

Premise: A recent survey of all auto accident victims in Dole County found that, of the severely injured drivers and front-seat passengers, 80 percent were not wearing seat belts at the time of their accidents

Conclusion: By wearing seat belts, drivers and front-seat passengers can greatly reduce their risk of being severely injured if they are in an auto accident.

Answer is asking for an additional premise to strengthen the conclusion:

(A) Of all the drivers and front-seat passengers in the survey, more than 20 percent were wearing seat belts at the time of their accidents. -  Perfect. Of all the people in the survey 80% of those injured didn't wear seat belts, 20% wore seat belts - which strengthens the conclusion 
(B) Considerably more than 20 percent of drivers and front-seat passengers in Dole County always wear seat belts when traveling by car. -  Always has no relevance, the argument talks about accidental impact. 
(C) More drivers and front-seat passengers in the survey than rear-seat passengers were very severely injured. -  Doesn't add anything to strengthen the conclusion 
(D) More than half of the drivers and front-seat passengers in the survey were not wearing seat belts at the time of their accidents.  Nothing to support or strengthen the conclusion 
(E) Most of the auto accidents reported to police in Dole County do not involve any serious injury.
 Out of Scope

rkassal · Answer

A is correct.
Lets say there were 100 cases of "serious" accident. Then 80 of those cases were not wearing seat-belts according to the author. But 20 were. So the author assumes that wearing seat-belts can prevent serious accidents. How can that be? There are 20 cases of serious accident that were wearing seat belts! Then how can the author claim that seat-belts can prevent serious accidents? The only way this can happen is if more than 20 people in the auto-accident survey were wearing seat belts and were not seriously hurt. Choice A provides us with that number- it says more than 20% of ALL accident cases were wearing seat-belts at the time of the accident. Now 20% of ALL cases has to be > 20% of serious cases since "serious cases" is a sub-group of all cases. 
Hence answer A.

vibhav · Answer

I was able to read option A by POE. but I still dont understand how option A works out. Can an expert comment pls?

GMATPill · Answer

This question is quite confusing - it's likely that the wording would be rephrased on the real exam. It's not clearly presented that there are other groups other than the "severely injured" group. What is the source?

The key point here is in how the information is provided and structured. The survey is for those who got into accident. Now, most readers make the incorrect connection between 'accident' and 'severely injured'. They think that 80% of people got into accident and were seriously injured, the remaining 20% did not get into accident and were safe.

That's incorrect.

The way the information is provided, they are saying that of those that are severely injured (we don't know what portion of the accidents resulted in SEVERE injury but let's say 60% for example or 60 people out of 100) -- 80% did not wear seat belts.

That means out of 60 seriously injured people (out of 100 total), 80% of these 60 did not wear seat belts. Or, 48 did not wear seat belts.

What's important to note is that 20% of these 60 (or 12 people) DID wear a seat belt and still got seriously injured.

So to summarize, 60 people were seriously injured (48 did not wear a seat belt while 12 did). The remaining 40 were more mildly injured and we have no data as to who wore or did not wear seat belts.

The argument is that wearing a seatbelt reduces the risk of SERIOUS injury. However, we know that 12 people wore a seatbelt and still got seriously injured. How do we know that wearing seat belt can reduce the risk?

Well, it must be the case that people wearing a seatbelt tended to have more mild injuries (part of the 40-person group, not the 60-person serious injury group).

So can we show that the breakdown for the serious injury was 
 80% no seat belt
20% seat belt

...and that the breakdown for the mild injury group was  
 <80% no seat belt and 
>20% seat belt?

If so that means if you wear a seat belt, you are more likely to be part of the mild injury group than the serious injury group.

KarishmaB · Answer

Responding to a pm:

First let's figure out the conclusion in short: If drivers are in an accident, they can reduce risk of severe injury by wearing seat belts.

Notice that the conclusion focuses on drivers who are in an accident, not on other drivers. The point is that if one is in an accident, seat belt can reduce risk of severe injuries. So to prove it, we need data on all drivers who were in an accident. 
When people are in an accident, they either suffer mild injuries or severe injuries (which could lead to death).

So if we know that of all who suffered severe injuries, only 20% were wearing seat belts, it doesn't help us conclude that wearing seat belts reduces risk of severe injuries. We need to know that of all who suffered mild injuries, how many were wearing seat belts. Say, of those who suffered mild injuries, only 10% were wearing seat belts, can we still say that seat belts reduce risk of severe injuries? No. Of those who suffered mild injuries, if 60% were wearing seat belts, it strengthens our conclusion.

Taking numbers, say 100 drivers were in an accident.
50 suffered mild injuries - Say, 30 were wearing seat belts
50 suffered severe injuries - Only 10 were wearing seat belts
We need this data to prove our conclusion - if one wears the seat belt, it reduces the risk of severe injuries.

semwal · Answer

suppose in a town there are 100 people driving vehicles, 40( more than 20 %) wore seat belts , 60 did'nt.
accidents take place.... 10 result in serious cases..... 2 were wearing seat belts 8 were not.....
chances of serious accident----- for those with seat belt- 2/40 ie 5%
 -------for those without seat belts- 8/60 ie 13.5 %.

hence conclusion true.....ans = A.............

Nightmare007 · Answer

I felt this to be a great question.
But a little time taking.
say 1000 total accidents occured.
100 of them S.Injured .
80 --> X seat belt.
20 ---> Seat belt.
Now,
Option A: for suppose its exactly 20% of people wore seat belt.
20 / 200 = 10% of accidents of seat belt are SI .
80 / 800 = 10 % of accidents of X Seat belt are SI
For suppose, it is less than 20% of people wore seat belt.
% of accidents of seat belt are SI Increases as 200 value increases while 20 remains constant.
Destroying the conclusion .
Hence, Answer should be A.

.

hellosanthosh2k2 · Answer

Hi,

This is pure Quants problem landed in CR bucket.

The argument wants to show wearing seat belts is safety.

how? by showing -

(no of serious accidents with seat belts / no of accidents with seat belts) < (no of serious accidents with NO seat belts / no of accidents with NO seat belts)

So if above ratio is true, wearing seat belt is safety and people are less prone to serious accidents

Given data: no of serious accidents with seat belts- 20%
no of serious accidents with NO seat belts - 80%

Let no of serious accidents be 10, so
no of serious accidents with seat belts- 2
no of serious accidents with NO seat belts - 8

Let number of total accidents be 100
no of accidents with seat belts = x
no of accidents with NO seat belts = 100 - x

And question is indirectly asking, what is the value of x or rather, what is range of x

now substitute in ratio equation we defined,
(no of serious accidents with seat belts / no of accidents with seat belts) < (no of serious accidents with NO seat belts / no of accidents with NO seat belts)
(2/x) < (8 / (100-x))
rearranging => 200 + 2x < 8x => 20 < x

So x (no of accidents with seat belts) > 20

Wow, this is what answer choice A says !! Bingo !! - safely eliminate other answer choices all we do in quants section - problem solving, once we find the right answer.

To be honest, I didnt get this question correct at first, by after reading all explanations, tried to come up with my own reasoning.

dhairya18 · Answer

Imagine 100 drivers in total get into accidents in Dole County.

SCENARIO A: Most people wear seat belts (Say, 90 out of 100)
Total drivers in accidents: 90 belted, 10 unbelted.

Now look at who gets severely injured:
Suppose 10 people get severely injured.
The study says 80% of them were unbelted = 8 unbelted people got severely injured.
That means 8 out of 10 unbelted drivers got severely injured (80% injury rate).
Only 2 out of 90 belted drivers got severely injured (2.2% injury rate).
Conclusion: Seat belts clearly protect you (2.2% vs 80%). The argument works!

SCENERIO B: Almost nobody wears seat belts (Say, only 20 out of 100)

Total drivers in accidents: 20 belted, 80 unbelted.
Now look at who gets severely injured:
Suppose 10 people get severely injured.
The study says 80% of them were unbelted = 8 unbelted people got severely injured.
That leaves 2 belted people who got severely injured.

Calculate the injury rates:
Unbelted injury rate: 8 out of 80 = 10%
Belted injury rate: 2 out of 20 = 10%
Conclusion: Belted and unbelted drivers get injured at the exact same rate (10%). Wearing a seat belt made zero difference!

Why is this an assumption?

The argument assumes Scenario A is true.
If Scenario B is true instead, the stat ("80% of injured people were unbelted") is meaningless because 80% of all drivers were unbelted anyway.

Therefore, for the argument to work, the overall percentage of drivers who wear seat belts in Dole County MUST be much higher than 20%.

Hellohello007 · Answer

Can someone please explain why not D please?

guddo · Answer

A recent survey of all auto accident victims in Dole County found that, of the severely injured drivers and front-seat passengers, 80 percent were not wearing seat belts at the time of their accidents. This indicates that, by wearing seat belts, drivers and front-seat passengers can greatly reduce their risk of being severely injured if they are in an auto accident. 
 
The conclusion above is not properly drawn unless which of the following is true?

The argument compares seat-belt use among the severely injured with the risk of severe injury. But knowing that only 20 percent of the severely injured wore seat belts tells us little unless we know  what proportion of all accident-involved drivers and front-seat passengers wore seat belts .

(A) Of all the drivers and front-seat passengers in the survey, more than 20 percent were wearing seat belts at the time of their accidents.

Correct.   Among the severely injured, only 20 percent were wearing seat belts. For this to support the claim that seat belts reduce severe injury, the proportion wearing seat belts among all accident victims must be higher than 20 percent. Otherwise, seat-belt wearers would not be underrepresented among the severely injured.

(B) Considerably more than 20 percent of drivers and front-seat passengers in Dole County always wear seat belts when traveling by car.

Incorrect. The relevant comparison is with people who were actually involved in the accidents surveyed, not with drivers and passengers in the county generally.

(C) More drivers and front-seat passengers in the survey than rear-seat passengers were very severely injured.

Incorrect. Rear-seat passengers are irrelevant to the conclusion about seat-belt use among drivers and front-seat passengers.

(D) More than half of the drivers and front-seat passengers in the survey were not wearing seat belts at the time of their accidents.

Incorrect. This does not establish that seat-belt wearers were less likely to be severely injured. The necessary threshold is whether more than 20 percent of all accident victims were wearing seat belts.

(E) Most of the auto accidents reported to police in Dole County do not involve any serious injury.

Incorrect. This does not connect seat-belt use with the likelihood of severe injury.

Answer: (A)

guddo · Answer

(D) is not enough because it only says that more than half of all drivers and front-seat passengers were unbelted.

But among the severely injured, 80 percent were unbelted. To show that seat belts reduce severe injury, we need to know that the unbelted made up less than 80 percent of all accident victims, which is the same as saying that more than 20 percent of all accident victims were wearing seat belts.

(D) could still be true even if 90 percent of all accident victims were unbelted. In that case, the fact that 80 percent of the severely injured were unbelted would actually make seat-belt users look worse, not better.

That is why (A) is required and (D) is not.

A recent survey of all auto accident victims in Dole County found that

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A recent survey of all auto accident victims in Dole County found that

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