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

icandy · Answer

Assumption Q based on connect the premise and conclusion or fill the logical gap.

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.

conty911 · Answer

i will go with C.

(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.-It contradicts the premise it cannot be more than 20% since 80% people in survey were not wearing
(B)Considerably more than 20 percent of drivers and front-seat passengers in Dole County always wear seat belts when traveling by car.---This doesnot tell us anything,maybe 40% even wore we are talking about people in survey.
(C) More drivers and front-seat passengers in the survey than rear-seat passengers were very severely injured.
--by wearing seat belts, drivers and front-seat passengers can greatly reduce their risk of being severely injured
This seems to connect the dots, if front seat passengers are seriously injured then seatbelt will surely help them.
(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.-grbgrgrbgrbgr again similar to B
(E) Most of the auto accidents reported to police in Dole County do not involve any serious injury.
o yea same thing happens in my county also

KapTeacherEli · Answer

Hi jitgoel,

This problem gives us evidence that 80% of injuries in car accidents are from folks not wearing seat belts. The argument's conclusion is that seat belts work. So, what's missing here? Well, we have no context about the 80%; it sounds scarily high, but we don't actually know that! The authors' assumption is that 80% of injuries makes up a disproportionate number of injuries to non-wearers. After all, if 80% of people don't wear seat belts, it's little surprise they suffered 80% of accidents! (B) tells us that this is not the case; the author's assumption that 80% is significant is in fact correct, and therefore so is his conclusion. (B) is the answer.

conty911 · Answer

Oops i completely missed this one.
Can you let me know why C is wrong?
I thought the question was asking for a premise which can strengthen the conclusion rather than an assumption.
As for (B), "Considerably more than 20 percent of drivers and front-seat passengers in Dole County always wear seat belts when traveling by car." i thought this this meant some percentage range from 20% to lets say 60% folks wear seat belts, however i'm still having hard time to find out how it is necessary for the conclusion?

KapTeacherEli · Answer

(C) is irrelevant because it relies on an unstated assumption similar to the one in the main argument--without knowing the total number of front seat drivers versus the number of rear seat passengers, the number of front and rear seat injuries don't actually tell us anything.

KapTeacherEli · Answer

Whoops, looks like I missed something on this one!

(B) doesn't actually have to be true here. The reason is the word that should have made me suspicious from the get-go: "always." We need more than 20% of Dole County drivers to be wearing seatbelts, yes--but it doesn't have to be the  same  20% on any given day. As long as more than 20% of the riders on the road are wearing their seatbelts, the argument is properly reasoned, so (B) is a (subtle) distortion.

(A), however, is the correct answer based on my reasoning above--which was the correct reasoning! Remember, the 80% that were injured is only a subset of those surveyed, the severely hurt group. We need to know that, among the group  not  severely injured, more than 20% were wearing seatbelts, which is what (A) gives us.

(C) is irrelevant as I said above--without relative numbers of front- and back- seat passengers, we don't know if more front- or back-seat injuries is actually an interesting result.

(D) is wrong because 49/51 and 51/49 splits of seatbelt-to-non-seatbelt-wearers are indistinguishable to us from the perspective of this article.

And, (E) is irrelevant, because in that more than half without serious injury, we don't know a thing about proportions who had seat belts.

Sorry for the confusion on the OA on this problem, and happy problem solving!

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.

mau5 · Answer

A more numeric approach:
The conclusion of the arguement is that  by wearing seat-belts, drivers and front-seat passengers can reduce the risk of being .... . 
Let's assume that out of all the people surveyed,say x, 100 were severly injured. So the remaining were not severly injured(Mild injury,no injury,etc).Now, out of these 100 people, 80 were not wearing seat belts at the time of accident. Thus, 20 were wearing seat belts and still got serious injuries. Now, to re-inforce/buttress the fact that wearing seat-belt greatly reduces the risk of being  severly injured  , the author would need support from the group of people who didn't suffer serious injury  because  they were wearing seat-belts.
Now, if option A is true, then that means that: # of people wearing seat belts > \frac{x}{5}  --> # of people wearing seat belts > 20 . This directly means that atleast some of the people who are from the  not serious injuries  group must have worn seat-belts, thus cementing the conclusion.

Also, as per Option D, we would have the condition : # of people  not  wearing seat belts > \frac{x}{2} . Just as above, we have x>100. Thus, # of people  not  wearing seat belts >50. However, we anyways know that the # of people  not  wearing seat belts is atleast 80. Thus, this option doesn't really add anything conclusive to cement the conclusion.

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.............

mpetwal · 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.

Total Accidents - 100
Acc with Serious injuries - 10
Acc W/O seat belt and serious injuries (80%) - 8
Acc With seat belt and serious injuries - 2
Total no of people who wear seat belt = 10 (Assumption)
Total no of people who don't wear seat belt = 90 (Assumption)
% of people who wear seat belt and still have fatal injuries = 2/10 = 20%
% of people who don't wear seat belt and have fatal injuries = 8/90 = 8.88%

Hence wearing seat belt increases the chance of fatal injuries in accident. DO NOT WEAR SEAT BELTS.

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.

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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