RC - Lyme Disease - GmatPrep

[as2764]

oh! then perhaps signing off every post with a "--ron" at the end for those who are unfamiliar with your style, though i can now tell your posts from others!

[RonPurewal]

oh! then perhaps signing off every post with a "--ron" at the end for those who are unfamiliar with your style, though i can now tell your posts from others!

ya, if this ever happens again i'll try something along those lines -- thanks for the suggestion. for now, tech support appears to have this problem sewed up.

[gmatwork]

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

Is the above conclusion - causal ? Why or why not?

Is the author assuming that suggested way is the ONLY way of getting the desired result??? (just like other causal conclusions in GMAT)

[gmatwork]

any thoughts why (a) and (d) are wrong?

[RonPurewal]

Is the author assuming that suggested way is the ONLY way of getting the desired result??? (just like other causal conclusions in GMAT)

in general -- whether on the gmat or in real life -- there is no assumption of exclusivity in cause-and-effect statements. in other words, saying that "a causes b" certainly does not imply that a is the only thing that causes b.

any thoughts why (a) and (d) are wrong?

(a) is incorrect because it's irrelevant.
we do need to know whether there is some overlap between the other populations and the white-footed mice, because the plan is, basically, to redirect deer ticks from white-footed mice to the other populations. however, this notion has nothing to do with the idea that the other populations are found ONLY where white-footed mice live.

there is an extensive discussion of (d) on the first page of this thread; please read it. thanks.

[gmatwork]

Is the given conclusion a causal conclusion or conditional?

To weaken a causal conclusion - we can do two things either show reverse causality or show that a third factor leads to both things that happened in the passage.

Power Score CR Bible talks about another way of weakening - causal conclusion ( X leads to Y) can be weakened by coming up with an alternate explanation or cause that leads to Y (as per your videos). I am not sure what to do about this concept that I have learned from Power Score. The book said that for causal conclusions ( X ->Y) GMAT assumes that X is the only possible cause for Y and an alternate explanation can weaken the causal conclusion. I am very confused now.

I still have a doubt regarding choice A - the key assumption that has been made in the current argument is that introduction of uninfected host population will lead to a diversion of some of the deer ticks from white foot mice to uninfected hosts, thereby leading to a reduction in number of infected larve. Now wouldn't having the two types of hosts in the same area mean that this diversion will happen and if these two types of hosts are in different areas, diversion will not occur.

I know that I am over thinking but still this is important to resolve, else I will pick up a trap answer.

[tim]

For what it's worth, i would say this is a conditional conclusion. "If X happens then Y will happen" is conditional. A causal conclusion would probably look more like "X and Y both happened, so X caused Y"..

A is wrong mainly because it's an example of "extreme" language, which you should avoid in an evaluate question. would it be helpful to know that populations of the other species are found ONLY in a particular area? ask yourself if the conclusion would change if they were found ONLY there versus found there as well as some random remote island somewhere. would ruling out the possibility of bacteria on the remote island really affect the conclusion?

[thanghnvn]

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 by feeding on infected white-footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. If the population of these species increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline.

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

(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.

this is very hard problem
the point is that if the availability of animals on which lavae feed on is so abandant that the lavae feed on a small part of infected mice and a small part of non infected mice, then the change in the number of non infected mice will not affect the number of infected deer tick and the argument fall apart.

is my thinking correct? pls confirm, thank you.

[RonPurewal]

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 by feeding on infected white-footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. If the population of these species increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline.

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

(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.

this is very hard problem
the point is that if the availability of animals on which lavae feed on is so abandant that the lavae feed on a small part of infected mice and a small part of non infected mice, then the change in the number of non infected mice will not affect the number of infected deer tick and the argument fall apart.

is my thinking correct? pls confirm, thank you.

even if you find that reasoning difficult to follow, you shouldn't have nearly as hard a time eliminating choice (a) because of "only". i.e., if those species are also found in other areas, who cares -- we only care about what happens in the areas where the mice live.

[asth678]

[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. (:

I am sorry but I still don't get how B is correct-Is it because earlier you had 10 ticks if you give them more food now there will be 100 ticks.Is there a way to look at this solution with numbers cause I cant seem to get the logic.I picked D for the same reason-If dicks could get infected by feeding on the deer the role of white mice is pointless.

[RonPurewal]

I don't want to make up numbers, because that's absolutely not what you should be doing here"”you should be working toward, not away from, developing an intuitive approach to CR. (In fact, even when there are actual statistics, you still shouldn't be doing arithmetic with them; you should be thinking about what they mean, and about why those particular statistics were chosen as opposed to others.)

Let's try another approach here: Since this is a "Whether" statement, let's just see what happens in the affirmative and negative cases of it. If those two lead to fundamentally different conclusions, then we have Something That Affects The Argument (= the correct answer).

Before considering those effects, make sure you understand how the argument proceeds in general. The basic idea is that you could "dilute" the presence of the bacterium by increasing the population of host animals other than white mice. I.e., if you increase the number of those animals"”without increasing the number of white mice proportionally"”then the ticks will spread out over that greater number of animals, reducing the % feeding on white mice and thus thinning out the population of the bacterium.

If (B) is a "yes", this means that the tick population is smaller than it could be, because there aren't enough host animals to go around. I.e., the tick population "wants" to get bigger, but simply can't, because there aren't enough host animals.
If that's the case, then introducing extra host animals won't spread the ticks out more thinly; it will just increase the total number of ticks! So the bacterium won't be affected.

Negative:
If (B) is a "no", then the tick population is not artificially small as a result of a imited # of host animals. In that case, the plan is likely to have the described effect.

Those are fundamentally contrasting outcomes, depending on whether (B) is true or false, so that means (B) affects the judgment.

[samwong]

I don't want to make up numbers, because that's absolutely not what you should be doing here"”you should be working toward, not away from, developing an intuitive approach to CR. (In fact, even when there are actual statistics, you still shouldn't be doing arithmetic with them; you should be thinking about what they mean, and about why those particular statistics were chosen as opposed to others.)

Let's try another approach here: Since this is a "Whether" statement, let's just see what happens in the affirmative and negative cases of it. If those two lead to fundamentally different conclusions, then we have Something That Affects The Argument (= the correct answer).

Before considering those effects, make sure you understand how the argument proceeds in general. The basic idea is that you could "dilute" the presence of the bacterium by increasing the population of host animals other than white mice. I.e., if you increase the number of those animals"”without increasing the number of white mice proportionally"”then the ticks will spread out over that greater number of animals, reducing the % feeding on white mice and thus thinning out the population of the bacterium.

If (B) is a "yes", this means that the tick population is smaller than it could be, because there aren't enough host animals to go around. I.e., the tick population "wants" to get bigger, but simply can't, because there aren't enough host animals.
If that's the case, then introducing extra host animals won't spread the ticks out more thinly; it will just increase the total number of ticks! So the bacterium won't be affected.

Negative:
If (B) is a "no", then the tick population is not artificially small as a result of a imited # of host animals. In that case, the plan is likely to have the described effect.

Those are fundamentally contrasting outcomes, depending on whether (B) is true or false, so that means (B) affects the judgment.

Sorry, but I'm having a really hard time understanding this problem even after reading all the previous posts.


If B is "yes", then introducing the OTHER host animals (without the bacterium) will increase the total number of ticks. However, the number of ticks WITH the bacterium will be less compare to the total number of ticks. This result seems to strengthen the conclusion rather than weaken it.

If B is "no", then introducing the OTHER host animals (without the bacterium) will not affect the total number of ticks. Thus, in this case, the number of ticks WITH the bacterium will remain the same. This results seems to weaken the conclusion rather than strengthen it.

What is wrong with my logic? Any help will be greatly appreciated. Thanks.

Ron, did you discuss this problem in the Thursday Study Hall?

[tim]

What's wrong with Ron's logic? :)

[samwong]

I don't want to make up numbers, because that's absolutely not what you should be doing here"”you should be working toward, not away from, developing an intuitive approach to CR. (In fact, even when there are actual statistics, you still shouldn't be doing arithmetic with them; you should be thinking about what they mean, and about why those particular statistics were chosen as opposed to others.)

Let's try another approach here: Since this is a "Whether" statement, let's just see what happens in the affirmative and negative cases of it. If those two lead to fundamentally different conclusions, then we have Something That Affects The Argument (= the correct answer).

Before considering those effects, make sure you understand how the argument proceeds in general. The basic idea is that you could "dilute" the presence of the bacterium by increasing the population of host animals other than white mice. I.e., if you increase the number of those animals"”without increasing the number of white mice proportionally"”then the ticks will spread out over that greater number of animals, reducing the % feeding on white mice and thus thinning out the population of the bacterium.

If (B) is a "yes", this means that the tick population is smaller than it could be, because there aren't enough host animals to go around. I.e., the tick population "wants" to get bigger, but simply can't, because there aren't enough host animals.
If that's the case, then introducing extra host animals won't spread the ticks out more thinly; it will just increase the total number of ticks! So the bacterium won't be affected.

Negative:
If (B) is a "no", then the tick population is not artificially small as a result of a imited # of host animals. In that case, the plan is likely to have the described effect.

Those are fundamentally contrasting outcomes, depending on whether (B) is true or false, so that means (B) affects the judgment.

Let me try again...

If the tick population is currently limited by the food source (if B is "YES"), then when you introduce more food (other host animals without the bacterium) the number of tick will increase because the ticks will feed on the extra food source. However, since the host animals do not carry the bacterium, the number of ticks that are infected will not increase. Thus, the number of infected ticks will be "diluted". This seems to achieve the conclusion. But, Ron said that the bacterium won't be affected in this case.

In contrast, if the tick population is currently not limited by the food source (if B is "No"), then when you introduce more food, the number of ticks will not increase because the ticks already have enough food. They are not likely going to feed on the new food source. Thus, the number of infected ticks will remain the same. This result weaken the conclusion. However, Ron said in this situation, the plan is likely to have the described effect.

Tim, I love your OG archer videos. Its always exciting to hear you explain OG problems. Great job! :o)

[RonPurewal]

If the tick population is currently limited by the food source (if B is "YES"), then when you introduce more food (other host animals without the bacterium) the number of tick will increase because the ticks will feed on the extra food source.

so far, so good...

--

However, since the host animals do not carry the bacterium, the number of ticks that are infected will not increase.

still good...
note "will not increase" --> i.e., the number will remain exactly the same. it certainly won't decrease.

--

Thus, the number of infected ticks will be "diluted".

nope.
as you wrote above, the number of infected ticks will stay the same. it won't go up -- but it won't go down, either.

In contrast, if the tick population is currently not limited by the food source (if B is "No"), then when you introduce more food, the number of ticks will not increase because the ticks already have enough food.

yes, up to there.

--

They are not likely going to feed on the new food source. Thus, the number of infected ticks will remain the same.

no. you are assuming that the ticks will simply ignore the newly introduced host animals.
that's not a reasonable assumption; after all, a host animal is a host animal. the only reasonable assumption here is that the ticks will spread across the entire host population, which now includes the extra host animals.

you are spreading the same number of ticks over a greater population of host animals; therefore, the density of the tick population goes down.
lower density of ticks per host animal + same number of host animals with the bacterium = less bacterium.

hope that helps. if that still doesn't make sense, then maybe tim can give it a try... or else just let it slide