RC - Lyme Disease - GmatPrep

[gagansb]

Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected whitefooted mice. However, certain other species on which the larvae feed do not harbor the bacterium. Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium would likely decline.

Which of the following it would be most useful to ascertain in evaluating the argument?

[editor: there were multiple errors in the original transcription, so i've copied and pasted the following answer choices from another source. in particular, the original transcription omitted the word "tick" after "deer" in 2-3 of the choices.
watch your transcriptions, people!]

(A) Whether populations of the other species on which deer tick larvae feed are found only in the areas also inhabited by white-footed mice.
(B) Whether the size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on.
(C) Whether the infected deer tick population could be controlled by increasing the number of animals that prey on white-footed mice.
(D) Whether deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed.
(E) Whether the other species on which deer tick larvae feed harbor any other bacteria that ticks transmit to humans.

[RonPurewal]

do you have a specific question about this problem? if you just post a problem, it's hard to tell exactly what you're asking.

are there two or three answers between/among which you're deliberating? is there something you don't understand about the correct answer?

please post back, with your question(s). thanks.

note:
takeaway:
this question prompt
Which of the following it would be most useful to ascertain in evaluating the argument?
is very closely related to FIND THE ASSUMPTION.
if you see this prompt, you should think about the same sorts of issues that you'd consider in a Find the Assumption question.


--

here's another page about the same question. they must be cutting their question writing budget.
post2001.html

[montz1]

do you have a specific question about this problem? if you just post a problem, it's hard to tell exactly what you're asking.

are there two or three answers between/among which you're deliberating? is there something you don't understand about the correct answer?

please post back, with your question(s). thanks.

note:
takeaway:
this question prompt
Which of the following it would be most useful to ascertain in evaluating the argument?
is very closely related to FIND THE ASSUMPTION.
if you see this prompt, you should think about the same sorts of issues that you'd consider in a Find the Assumption question.


--

here's another page about the same question. they must be cutting their question writing budget.
post2001.html

For the question posted by gagansb...

I picked D because it helps to establish whether there is an alternate way through which ticks can acquire the bacterium and thus we can strengthen or weaken the argument.
My reasoning:
Increasing the population of other species that do not harbor the bacterium may help in decreasing the number of ticks that acquire the bacterium - but only when the ticks are in the larvae stage, if deer ticks that were not infected as larvae can become infected as adults, then they do acquire the bacterium and hence the argument is weakened.

OA is B. I am not clear why the size of the deer population is relevant.
The deer population may be limited by the availability of animals on which ticks feed on in larvae stage, but if all these animals are white-footed mice (or any other species that harbor the bacterium) the ticks would acquire the bacterium and in that case the entire deer population is infected. But if all these animals are the 'other species' then ticks would not acquire the bacterium.
So, only the availability of animals does not help in drawing any conclusion, we need to know whether the animals are white-footed mice or the other species.

Can you please explain what is wrong with my reasoning and why B is the correct answer?

[RonPurewal]

I picked D because it helps to establish whether there is an alternate way through which ticks can acquire the bacterium and thus we can strengthen or weaken the argument.
...
My reasoning:
Increasing the population of other species that do not harbor the bacterium may help in decreasing the number of ticks that acquire the bacterium - but only when the ticks are in the larvae stage, if deer ticks that were not infected as larvae can become infected as adults, then they do acquire the bacterium and hence the argument is weakened.

nah. you're thinking too hard.

the conclusion of the argument is:
if the population of these other species were increased, the number of ticks acquiring the bacterium would likely decline.

you are mistakenly thinking that ANYTHING that would increase the # of infected ticks is irrelevant to this argument.

you have to stick to this conclusion, though. anything that does not have to do with the CONNECTION between INCREASING THE POPULATION OF OTHER HOST SPECIES and the # of infected ticks ... is irrelevant.

analogy:
let's say the conclusion of an argument is if we institute a gmat prep program at State University, the students' gmat scores will go up.

if i make a statement such as students at State U have recently been getting higher gmat scores because they're studying on their own, this has NO BEARING AT ALL on the conclusion above.
it has to do with increasing gmat scores, but not with the CONNECTION between instituting a prep program and increasing those scores.

OA is B. I am not clear why the size of the deer population is relevant.
The deer population may be limited by the availability of animals on which ticks feed on in larvae stage, but if all these animals are white-footed mice (or any other species that harbor the bacterium) the ticks would acquire the bacterium and in that case the entire deer population is infected. But if all these animals are the 'other species' then ticks would not acquire the bacterium.
So, only the availability of animals does not help in drawing any conclusion, we need to know whether the animals are white-footed mice or the other species.

Can you please explain what is wrong with my reasoning and why B is the correct answer?

heh.

your problem here is that you were looking at the wrong words. someone mistranscribed the problem.
see edits above. (b) should say "deer tick population", not just "deer population".

hope that makes more sense now.

[acethegmat]

[RON: this is my post; i'm not sure why it's credited to another user.]

I am unable to understand how B addresses the problem.
Even though the number of larvae increases, the number of infected larvae would be less, which is related to the conclusion.

the reason why you don't see how (b) addresses the problem is because you're making the same questionable assumption that the argument makes! in fact, here you are making the precise assumption that is called into question by choice (b).

in particular, you are saying "the number of infected larvae would be less" -- this involves an assumption that the population of deer ticks will diffuse and spread out.

choice (b) presents the possibility that the deer tick population is currently limited by the availability of hosts. if that's the case, then increasing the number of hosts will NOT cause the population to dissipate or spread out -- instead, you'd just get exponential population growth, with the same density of deer ticks on disease-causing hosts (as well as more of them on your newly introduced hosts).

D addresses the issue stating that whether the larvae feed increases or not, it will not help if the bacterium is caused through the deer itself.

nope, (d) is irrelevant because it has nothing to do with the substance of the actual argument, which deals with the result of introducing additional host species for the larval tick.

you are making the mistake of thinking that any factor that affects the infected deer tick population, in any way, is relevant to this argument.
that's not true; the only things that are relevant are those that directly have to do with whether increasing the number of larval hosts will increase the infected population. if you pick a choice that affects the infected population in some other way that doesn't have anything to do with larvae, then that choice is irrelevant.

if you don't see what i'm saying, then here is an analogy that's almost certainly easier to understand:

argument:
studies have shown that increased protein intake promotes weight gain. therefore, if i increase my protein intake by eating egg whites every morning for breakfast, i will be successful in gaining weight.
* whether eating egg whites will cause a feeling of satiation that will make me eat less protein throughout the rest of the day --> this is relevant, because it actually deals directly with the effect of egg whites on my protein intake.
* whether there are other sources of protein that will be better than egg whites for achieving my goal --> irrelevant, since the passage isn't about meeting my goal in general; the passage is only about whether egg whites, in particular, will help me meet that goal.

No?

no. (:

[as2764]

Hi - Can an expert please explain why B? I am still debating between B and C.

I came up with the following assumptions:
1. deer ticks have no specific preference towards white-footed mice or other food sources.
2. both food sources - mice and others - are equally accessible to deer ticks.

I see the 'connection' described in the conclusion, but even C has some relevance as it says that the infected deer tick population can be controlled by making them compete with another parasite that also feeds on white-footed mice, making the ticks feed on an alternate food source now abundantly available. So, shouldn't this have an impact (decrease) on the number and/or percentage of deer ticks acquiring the bacterium, and hence the number of humans being affected by them?

This really is a mind-bender.

[tim]

one reason why C is no good is that it does nothing to address the effect of the other species' increase in population. if C does anything it just gives a generic event that would cause the infected population to decrease; it does not address the cause and effect relationship present in the argument's conclusion..

[as2764]

one reason why C is no good is that it does nothing to address the effect of the other species' increase in population. if C does anything it just gives a generic event that would cause the infected population to decrease; it does not address the cause and effect relationship present in the argument's conclusion..

but isn't that what we're trying to find - what affects the infected population?
and couldn't an alternate cause:
-when eliminated strengthen the conclusion?
-that affects the %-age of infected population weaken the conclusion instead of the cause (increase in population of other species) mentioned in the conclusion?

in fact, as we see below, i think (B) affects the size of the deer tick population and not the %-age of the deer tick population that is infected, thus the latter will determine the likelihood/unlikelihood of the conclusion.

(B)Whether the size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on.
(C) Whether the infected deer tick population could be controlled by increasing the number of animals that prey on white-footed mice

[mschwrtz]

but isn't that what we're trying to find - what affects the infected population?

No, that's not what we're trying to figure out. "Which of the following it would be most useful to ascertain in evaluating the argument?" means something like "Which answer would help determine whether this argument is sound?" As Ron suggests, this means something like "Which answer tells you whether some assumption of the argument is true?"

An alternative cause for the decrease in the number of infected deer would be relevant if the conclusion of this argument were that an increase in the number of certain kinds of tick hosts had led to a decrease in the number of infected deer. But that is not the conclusion.

An alternative path to decreasing the number of infected deer would be relevant if the conclusion of this argument were that increasing the number of certain kinds of tick hosts were the best way to decrease the number of infected deer. But that is not the conclusion.

The conclusion here is simply that increasing the number of a certain type of tick host would reduce the number of infected deer. Other means to achieve that end are mostly irrelevant here. See Ron's account of D above.

Finally, any time the evidence is about proportions/percents and the conclusion is about numbers (or vice versa), the argument assumes something about the size of the whole(s), often that the whole stays the same size or that the wholes are similarly sized. In this case, the argument is that decreasing the percent of deer ticks carrying the bacterium will decrease the number of deer infected with the bacterium. This assumes that the number deer ticks will not be much larger when percentage of ticks carrying the bacterium decreases.


and couldn't an alternate cause:
-when eliminated strengthen the conclusion?
-that affects the %-age of infected population weaken the conclusion instead of the cause (increase in population of other species) mentioned in the conclusion?

in fact, as we see below, i think (B) affects the size of the deer tick population and not the %-age of the deer tick population that is infected, thus the latter will determine the likelihood/unlikelihood of the conclusion.

[as2764]

In this case, the argument is that decreasing the percent of deer ticks carrying the bacterium will decrease the number of deer infected with the bacterium. This assumes that the number deer ticks will not be much larger when percentage of ticks carrying the bacterium decreases.

i thought the argument is that increasing the population of non-infected hosts/species and all else remaining the same, can the percentage of deer ticks acquiring the bacterium decrease?

very confused???

[RonPurewal]

i highlighted the problem in blue:

i thought the argument is that increasing the population of non-infected hosts/species and all else remaining the same, can the percentage of deer ticks acquiring the bacterium decrease?

here's what it says in the original prompt:

Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium would likely decline.

remember -- on CR problems, *NEVER* confuse percentages with numbers.
that's an important point on quant, too (especially DS problems with percentages), but it's a focal point of a great many, perhaps even most, CR problems that feature statistics.

[as2764]

good catch, Ron. thanks!

BUT, the question still remains that isn't the argument that increasing the population of non-infected hosts/species and all else remaining the same, can the number of deer ticks acquiring the bacterium decrease?

appreciate inputs

[RonPurewal]

good catch, Ron. thanks!

BUT, the question still remains that isn't the argument that increasing the population of non-infected hosts/species and all else remaining the same, can the number of deer ticks acquiring the bacterium decrease?

appreciate inputs

yeah. that's why (b) is the correct answer.
see my post above, which, weirdly, was credited to another poster -- especially this excerpt

choice (b) presents the possibility that the deer tick population is currently limited by the availability of hosts. if that's the case, then increasing the number of hosts will NOT cause the population to dissipate or spread out -- instead, you'd just get exponential population growth, with the same density of deer ticks on disease-causing hosts (as well as more of them on your newly introduced hosts)

[as2764]

choice (b) presents the possibility that the deer tick population is currently limited by the availability of hosts. if that's the case, then increasing the number of hosts will NOT cause the population to dissipate or spread out -- instead, you'd just get exponential population growth, with the same density of deer ticks on disease-causing hosts (as well as more of them on your newly introduced hosts)

from the above, what i understood is that both sides of the causality in the conclusion have to be addressed in the correct answer, and that outside info that affects half the story is irrelevant. your above explanation is the key to the right answer.

after an hour of analysis, i'm finally convinced that (b) is the solution.

Ron - to avoid such technical glitches and confusion, it might help us students if you could add a signature to your replies.

thanks a lot

[RonPurewal]

heh, i suppose i'll have to learn how to make a signature. (i know pretty much nothing about computers and technology.)

... although making a signature probably wouldn't help with that sort of glitch: if the system doesn't think i'm the one who made the post, it won't use my signature, even if i've made one. i.e., it would actually use the signature of the user to whom the post is attributed.