Bicycle Safety expert: Bicycling on the left half of the road is much

Question

Bicycle Safety expert: Bicycling on the left half of the road is much more likely to lead to collisions with automobiles than is bicycling on the right. After all, in three different studies of bicycle-automobile collisions, the bicyclist was riding on the left in 15, 17 and 25 percent of the cases respectively.

Skeptic: But in places where a comparatively high percentage of bicyclists used to ride on the left, there was suprisingly little decrease in collisions between bicyclists and automobiles after bicycling on the left was made illegal.

One reason the strength of the bicycle safety expert's argument cannot be evaluated is that

(A) The statistics cited in support of the conclusion is that bicycling on the left is more likely to lead to collisions with automobiles already pressupose the truth of the conclusion.

(B) The statistics it cites do not include the percentage of bicycling that took place on the left.

(C) No statistics are provided on the proportion of bicycle accidents that are due to bicycle automobile collisions.

(D) Bicycling on the left is singled out for criticism without consideration of the other bicycling practices that are unsafe.

(E) It does not distinguish between places in which bicycling on the left is legal and places in which it is illegal.

ashutosh22 · Accepted Answer

it is 25 and not 75.

Anyway to answer this, you need to see the percentage of people who are using left or right lanes.

Case 1: 90K people use Left.....10K people use Right
 100 accident occurred 
 (15 to 25) on Left..............(85 to 75) on Right
=> Left is REAL Safe (25 out of 90K) 
Case 2: 10K people use Left.....90K people use Right
 100 accident occurred 
 (15 to 25) on Left..............(85 to 75) on Right
=> Left is not that Safe ( 25 out of 10 K)

One need to visualize that absolute percentage can be misleading. To compare you need weighted percentage.

Choice B just attacks that part.
I hope that helps.

arjunbt · Answer

B is appropriate because the safety expert just says "that the bicyclist was riding on the left in 15,17 and 25 percent of the Total cases respectively", here the expert is not giving any information about how much % of the cyclists were riding on left side.
if just 1% of the riders were on left side and 99% on right side, then 25% of the accidents are caused by just 1% of the people as per his statistics.

Hope my answer clears your doubt

Priyanka2011 · Answer

Hey

why is B appropriate ? Can someone explain ?

synfist · Answer

Conclusion:
If riding on the right leads to collisions 50 times (out of 100)
Then riding on the left leads to at least 51 collisions (out of 100)

Evidence Given:
In 3 studies 15/100 , 17/100, 25/100 collisions included left riding.

It is possible that all 100 in each of the cases were riding on left => weak support or not enough data to support
It is possible that only 15,17,25 respectively were riding on left => strong support for conclusion

tuanquang269 · Answer

I am still confused about this problem, can anyone explain more clearly.

The accident on the left is 15,17, and 75 percent of all case accident. So, the remain percent belongs to on the right. why argument said bicycling on the left have more accident than do on the right?

Practicegmat · Answer

Thanks for the explanation! Makes sense 
But then it looks like the argument put forth by the skeptic is not at all needed here ( the legal and illegal part ).. am I right .. its just an extra information to confuse people ..Please correct me if I am wrong

ashutosh22 · Answer

Yes you are right. That information won't play much part here. More so because the question was:
 "One reason the strength of the  bicycle safety expert's argument  cannot be evaluated is that"

So we have to evaluate the perspective of Bicycle Safety expert and not of Skeptic.

Cheers.

eiffel · Answer

still I cant understand, may please somebody help me more .

Nevernevergiveup · Answer

This question is a tough nut to crack.
Can you explain what you are not able to understand?

eiffel · Answer

This part of information '' the bicyclist was riding on the left in 15,17 and 25 percent of the cases respectively ''.
mention that rate of collision so why B is correct answer

Nevernevergiveup · Answer

This info seems to indicate an evidence against the expert conclusion. It makes us feel actually the very less no of accidents occur on left side of the road. but we cannot evaluate the same unless we have some additional info as to whether how many people walk on the left side. This is already explained above as follows Therefore we cannot evaluate the expert argument as indicated in option B. (B) The statistics it cites do not include the percentage of bicycling that took place on the left I hope this helps.

kornn · Answer

Dear  VeritasKarishma   IanStewart ,

Q1. What is the role of Skeptic here?
I know Skeptic is trying to counter Bicycle Safety expert. 
But I don't see how his/her counterargument helps in any way to solve or answer this problem!

Q2. Does Skeptic imply that collisions between bicyclists and automobiles is INDEPENDENT of whether riding left or right? (Because after bicycling on the left was made illegal " there was surprisingly LITTLE DECREASE in collisions ". So riding either left or right has no effect at all?)

Thank you!

KarishmaB · Answer

The skeptic is a distraction for you. You have to focus on the expert's argument and figure out why the data he has given is incomplete (so it cannot be evaluated).
He says " in three different studies of bicycle-automobile collisions , the bicyclist was riding on the left in 15,17 and 25 percent of the cases respectively"
So out of 100 collisions in study 1, in 15 the bicyclist was riding on the left. That seems like a small number. But if we were to know that only 1% people ride on the left but 15% accidents happened with left side riders, then we know that left side riding might be more dangerous. But what if 90% people ride on the left side but only 15% collisions were with left side riders? Then it seems to imply that left side riding is much safer.

Since the % of people riding on left is not given, we can unable to evaluate the argument.

Raman109 · Answer

Understanding the argument - 
Bicycle Safety expert: Bicycling on the left half of the road is much more likely to lead to collisions with automobiles than is bicycling on the right. After all, in three different studies of bicycle-automobile collisions, the bicyclist was riding on the left in 15, 17 and 25 percent of the cases respectively.

It means there were 100 accidents, so out of 100 accidents each time, there were 15, 17, and 25 counts. 
No, suppose there are 1000 cyclists overall, and out of 1000, 900 (which is 90%) ride on the left side; then the "15, 17, and 25" is a comparatively smaller number, but let's say that out of 1000, 25 (which is 2.5%) rides on the left side, then "15, 17, and 25" are pretty dangerous.

Skeptic: But in places where a comparatively high percentage of bicyclists used to ride on the left, there was suprisingly little decrease in collisions between bicyclists and automobiles after bicycling on the left was made illegal.

One reason the strength of the bicycle safety expert's argument cannot be evaluated is that

(A) The statistics cited in support of the conclusion that bicycling on the left is more likely to lead to collisions with automobiles already presuppose the truth of the conclusion. This is not a circular argument. An example of a circular argument is that you should trust the news because it is always reliable.

(B) The statistics it cites do not include the percentage of bicycling that took place on the left. - Yes. 2.5% or 90%?

(C) No statistics are provided on the proportion of bicycle accidents that are due to bicycle automobile collisions. - out of scope.

(D) Bicycling on the left is singled out for criticism without consideration of the other bicycling practices that are unsafe. - "Other bicycling practices " are out of scope.

(E) It does not distinguish between places in which bicycling on the left is legal and places in which it is illegal. - Skeptic's argument is out of the scope of the question.

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Bicycle Safety expert: Bicycling on the left half of the road is much

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