Number of subway riders

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by trangle.nh » Sat Jul 02, 2011 1:49 am
lunarpower wrote:
Geva@MasterGMAT wrote: Not a very good question, IMHO. It's trying to play on the "reported number is not the same as real number" issue
nope.

i think you may be reading a little bit too much into this question, and/or hypothesizing interpretations that are not the most likely ones for the statements at hand.
bear in mind how discrepancy problems work: you just have to ascertain exactly which discrepancy you're supposed to explain, and then pick the answer choice that most directly leads to the apparently contradictory effect.

in this case, the weird contradiction that you have to explain is this:
-- signs were erected warning tourists about pickpocketing
BUT
-- pickpocketing actually increased.

therefore, you just have to find some consideration that reasonably explains why the warning signs would actually facilitate pickpocketing.
choice (c) explains this quite well -- if tourists are rummaging through their pockets, then pickpockets can simply watch them and know exactly where their valuables are kept, therefore making the pickpockets' job much, much easier.

this problem has nothing to do with "actual versus reported cases", as that distinction is not mentioned anywhere in the passage.

why we have to :"find some consideration that reasonably explains why the warning signs would actually facilitate pickpocketing".

we can simple find another reason that can explain for the increase of the number of pickpoketing during the periods of the signs, not neccesarily " why signs facilitate pickpocketing".

Pleaze notice that: the last sentence says "a per-capita rate"? Please explain this phrase to have better explanation!

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by trangle.nh » Sat Jul 02, 2011 1:52 am
At lease " per capita rate" help to eliminate A & B!!!?

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by sameerballani » Sat Jul 02, 2011 4:53 am
Two opposing views are good. Lets wait for an expert comment.

The reason we need to have that the warning signs actually facilitate pickpocketing is probably we need to focus/solve the discrepancy that how come an action intended to show positive effects resulted in the opposite and negative outcome.
trangle.nh wrote:
lunarpower wrote:
Geva@MasterGMAT wrote: Not a very good question, IMHO. It's trying to play on the "reported number is not the same as real number" issue
nope.

i think you may be reading a little bit too much into this question, and/or hypothesizing interpretations that are not the most likely ones for the statements at hand.
bear in mind how discrepancy problems work: you just have to ascertain exactly which discrepancy you're supposed to explain, and then pick the answer choice that most directly leads to the apparently contradictory effect.

in this case, the weird contradiction that you have to explain is this:
-- signs were erected warning tourists about pickpocketing
BUT
-- pickpocketing actually increased.

therefore, you just have to find some consideration that reasonably explains why the warning signs would actually facilitate pickpocketing.
choice (c) explains this quite well -- if tourists are rummaging through their pockets, then pickpockets can simply watch them and know exactly where their valuables are kept, therefore making the pickpockets' job much, much easier.

this problem has nothing to do with "actual versus reported cases", as that distinction is not mentioned anywhere in the passage.

why we have to :"find some consideration that reasonably explains why the warning signs would actually facilitate pickpocketing".

we can simple find another reason that can explain for the increase of the number of pickpoketing during the periods of the signs, not neccesarily " why signs facilitate pickpocketing".

Pleaze notice that: the last sentence says "a per-capita rate"? Please explain this phrase to have better explanation!

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by Ian Stewart » Sat Jul 02, 2011 4:57 am
I posted a reply about this question on gmatclub, so I'll just copy an edited version here:

_______


I don't think this is a good question at all; I can justify almost all of the answer choices by making appropriate assumptions, yet can justify none of them without making assumptions.

Something must have changed since the signs were erected for the pickpocketing rate to have changed, so we're looking for an answer which describes a potentially relevant change. If "Central Station has become much more attractive to tourists from out of town" (where else would tourists be from?) then the population of potential victims has changed; it's certainly reasonable to think that the pickpocketing rate might therefore change. Answer A seems like a fine answer to me. This has nothing to do with 'common stereotypes' [I was replying to an MGMAT instructor who said that this answer choice was a trap answer based on common 'stereotypes' about tourists' vulnerability to pickpocketing] and all to do with population bias; if you do an experiment on one population, you can reasonably expect different results if you do the same experiment on a different population.

Answer B also describes a change since the signs were posted. It's certainly not far-fetched to think that pickpockets can operate more easily in a crowded environment, so B seems like a justifiable answer.

Answer C suggests that the signs are actually working; passengers are more vigilant about their possessions because of the warnings. The justification for answer C in the OE is, to be generous, tenuous, and is based on just as many assumptions as would be a justification for the other plausible answers.

I'm not sure why no one has considered D here. If fewer pickpockets are being prosecuted/convicted, then it's reasonable to think there will be fewer pickpockets in jail and more pickpockets in Central Station, and further there will be less of a deterrent to pickpocketing if there is less reason to fear conviction. It seems like a possible explanation for the increase in pickpocketing incidents.

E is the only answer that I think can be discarded out of hand, since it doesn't describe anything that has necessarily changed since the introduction of the signs.

I suppose the OE rules out B and D because they don't relate the posting of the signs to the increase in pickpocketing incidents, but it's not clear from the language of the question that we need to do that; any alternate explanation is enough to explain the 'discrepancy', whether that explanation relates to the signs or not. If we need to explain why the signs may have actually helped the pickpockets, the question needs to say that.
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by mriiidula » Sat Jul 02, 2011 5:00 am
Ian Stewart wrote:
I don't think this is a good question at all; I can justify almost all of the answer choices by making appropriate assumptions, yet can justify none of them without making assumptions.

Answer B also describes a change since the signs were posted. It's certainly not far-fetched to think that pickpockets can operate more easily in a crowded environment, so B seems like a justifiable answer.
Exactly. I picked 'B' *grumbles*
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by trangle.nh » Sat Jul 02, 2011 6:19 am
I think one of the lesson can be drawn from this Q is: when consider an answer, the only changed thing is the thing that is said to have change in the answer????

More specific:
Answer A& B try to specify the increase in the number of riders
---> Number of riders increase ----> pickpocketed per-capita rate decrease ---> eliminated A&B
Number of thief unchanged

Anyway, agree with Ian: answers can only be justified or eliminated if there are additional assumptions.

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by mirantdon » Sat Jul 02, 2011 7:07 am
yes i went with B too .
Question was certainly dicey

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by sameerballani » Sat Jul 02, 2011 7:35 am
I went with D when I attempted this.

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by Geva@EconomistGMAT » Sun Jul 03, 2011 1:04 am
lunarpower wrote:
Geva@MasterGMAT wrote: Not a very good question, IMHO. It's trying to play on the "reported number is not the same as real number" issue
nope.

i think you may be reading a little bit too much into this question, and/or hypothesizing interpretations that are not the most likely ones for the statements at hand.
bear in mind how discrepancy problems work: you just have to ascertain exactly which discrepancy you're supposed to explain, and then pick the answer choice that most directly leads to the apparently contradictory effect.

in this case, the weird contradiction that you have to explain is this:
-- signs were erected warning tourists about pickpocketing
BUT
-- pickpocketing actually increased.

therefore, you just have to find some consideration that reasonably explains why the warning signs would actually facilitate pickpocketing.
choice (c) explains this quite well -- if tourists are rummaging through their pockets, then pickpockets can simply watch them and know exactly where their valuables are kept, therefore making the pickpockets' job much, much easier.

this problem has nothing to do with "actual versus reported cases", as that distinction is not mentioned anywhere in the passage.
The question stem merely reads "Which of the following, if true, helps to explain the discrepancy pointed out in the passage?

Nothing in the question stem says that the contradiction needs to be explained only "internally" (i.e. explain why the signs themselves facilitate pickpocketing) - just that the discrepancy between the erecting of signs (a positive effect) and an increase in pickpocketing (a negative effect) needs to be explained. We do not have to assume that the signs themselves are the cause of the negative effect to do so; if an answer choice had said "in the last year, the train station has become the resting place for a clan of notoriously-hard-to-detect pickpockets from the planet Zorg", that answer choice would also explain the discrepancy quite well.

For C to be the best answer, the question stem needs to state that assumption that the signs indeed are the cause behind the rise in pickpocketing rate and nothing else. As is, C requires an additional step, and thus there are several answer choices that are as equally good (or as equally bad) as C - A, B, and D can also serve as the answer, with an additional step. I repeat, not a very good question at all.
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by lunarpower » Sun Jul 03, 2011 3:39 am
i am posting from halfway around the world, because i see that there has been a flurry of messaging about this question.

i think that ian's complaint (above) is legitimate -- i.e., the problem isn't specific enough to definitively relate the increase in pickpocketing to the erection of the signs.
in other words, the problem just says "in the year since the signs were erected" -- a year is plenty of time for other things to have caused the rate to increase.

therefore, i think that we should change the problem as follows:
Last year, after the number of subway riders who had had their pockets picked at Central Station had risen to an all-time high, the transit authority erected signs in Central Station telling riders to beware of pickpockets. Immediately upon the erection of the signs, though, the per-capita rate at which riders' pockets were picked rose to twice its original value.

if this is the new statement of the problem, then the OA becomes much less questionable, because the rise in the rate of pickpocketing is now known to be a direct and immediate result of the posting of the new signs.

we'll make these changes.
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