Critical Reasoning

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 and hence the number of people contracting Lyme disease-would
likely decline. Which of the following, if true, most strengthens the argument?

A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes
Lyme disease in humans.
B. There are no known cases of a human's contracting Lyme disease through contact with
white-footed mice.
C. A deer tick feeds only once while in the larval stage.
D. A single host animal can be the source of bacteria for many tick larvae.
E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks
transmit to humans

I am yet to come across an explanation that is convincing.

OA after some dicussion.

Between [spoiler]C/E[/spoiler] will choose C

IMO C

This eliminates one possibility, which can weaken the conclusion.
The possibility is that if deer tick also feeds in other stages, then increase in the population of other species may not actually enforce the indented effect

Rest all options look irrelevant/out of scope.

You'll find several experts' explanations here: https://www.beatthegmat.com/lyme-disease ... 47250.html

zaarathelab wrote: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 and hence the number of people contracting Lyme disease-would
likely decline. Which of the following, if true, most strengthens the argument?

A. Ticks do not suffer any adverse consequences from carrying the bacterium that causes
Lyme disease in humans.
B. There are no known cases of a human's contracting Lyme disease through contact with white-footed mice.
C. A deer tick feeds only once while in the larval stage.
D. A single host animal can be the source of bacteria for many tick larvae.
E. None of the other species on which deer tick larvae feed harbor other bacteria that ticks
transmit to humans

I am yet to come across an explanation that is convincing.

OA after some dicussion.

When a CR proposes a plan:
The PLAN = the premise.
The GOAL = the conclusion.

PLAN: Increase the population of species not infected with the bacterium that causes Lyme disease.
GOAL: Decrease the number of ticks acquiring the bacterium and thus the number of humans contracting Lyme disease.

Which answer choice suggests that the plan WILL WORK?

C. A deer tick feeds only once while in the larval stage. Consider the opposite extreme. If a deer tick feeds hundreds of times a day, then increasing the population of other food sources will likely have little effect: with so many feedings, at some point a deer tick is likely to feed off an infected white-footed mouse. But if a deer tick feeds ONLY ONCE, then the odds that it will feed off a white-footed mouse greatly DECREASE, suggesting that the PLAN WILL WORK: one feeding + lots of non-infected food sources = decreasing the likelihood that a deer tick will get infected.

The correct answer is C.

Thanks Mitch

OA is indeed C

GMATGuruNY wrote: When a CR proposes a plan:
The PLAN = the premise.
The GOAL = the conclusion.

PLAN: Increase the population of species not infected with the bacterium that causes Lyme disease.
GOAL: Decrease the number of ticks acquiring the bacterium and thus the number of humans contracting Lyme disease.

Which answer choice suggests that the plan WILL WORK?

C. A deer tick feeds only once while in the larval stage. Consider the opposite extreme. If a deer tick feeds hundreds of times a day, then increasing the population of other food sources will likely have little effect: with so many feedings, at some point a deer tick is likely to feed off an infected white-footed mouse. But if a deer tick feeds ONLY ONCE, then the odds that it will feed off a white-footed mouse greatly DECREASE, suggesting that the PLAN WILL WORK: one feeding + lots of non-infected food sources = decreasing the likelihood that a deer tick will get infected.

The correct answer is C.

Hi Mitch,
While I understand your above explanation, I'd like to know why B is wrong ?

Isn't this CR a CAUSAL ARGUMENT (If X then Y) ? If so, then B seems to indicate that there is LIKELY no other reason for Y to happen!

Please explain how it's incorrect!

RBBmba@2014 wrote:Hi Mitch,
While I understand your above explanation, I'd like to know why B is wrong ?

Isn't this CR a CAUSAL ARGUMENT (If X then Y) ? If so, then B seems to indicate that there is LIKELY no other reason for Y to happen!

Please explain how it's incorrect!

It is stated as a PREMISE that Lyme disease is caused by a bacterium transmitted to humans BY DEER TICKS.
Answer choice B -- which indicates that Lyme disease is not transmitted to humans by white-footed mice -- seems to strengthen this premise.
A premise is a FACT.
It cannot be strengthened.
Eliminate any answer choice that attempts to strengthen a premise.
Eliminate B.

GMATGuruNY wrote:It is stated as a PREMISE that Lyme disease is caused by a bacterium transmitted to humans BY DEER TICKS.
Answer choice B -- which indicates that Lyme disease is not transmitted to humans by white-footed mice -- seems to strengthen this premise.
A premise is a FACT.
It cannot be strengthened.
Eliminate any answer choice that attempts to strengthen a premise.
Eliminate B.

Got it.
Just a quick clarification reqd. This CR seems to be a CAUSAL ARGUMENT (If X then Y). Right ?

If yes, then it appears that we're NOT dealing with this CAUSAL CR in the conventional way (re identifying that there is NO other reason to cause Y or Reverse causation doesn't hold good) to tackle CAUSAL ARGUMENTS such as If X then Y.

Correct me please if wrong!

P.S: If I interpret B: If one of the ways of acquiring a disease is reduced, it'll LIKELY lead to a DECLINE in the occurrence of that disease, irrespective of whether there are other ways to acquire that disease or not. Thus B DOESN'T really seem to strengthen the CONCLUSION -- B becomes somewhat IRRELEVANT. Will this reasoning also work to ELIMINATE B ?

Hi Verbal Experts,
Could you please share your thoughts on my above concerns ?

Look forward to your feedback. Much thanks in advance!

Just a quick clarification reqd. This CR seems to be a CAUSAL ARGUMENT (If X then Y). Right ?

Typically a causal argument will involve an observed correlation: B seems to increase as A increases, therefore, A causes B. And you can weaken that argument by showing that, in fact, it's B that causes A, or there's some other underlying cause.

However, in this case, we have a proposed plan with a predicted outcome, so we wouldn't necessarily employ the same logic we'd use in an argument that involved an observed correlation.

P.S: If I interpret B: If one of the ways of acquiring a disease is reduced, it'll LIKELY lead to a DECLINE in the occurrence of that disease, irrespective of whether there are other ways to acquire that disease or not. Thus B DOESN'T really seem to strengthen the CONCLUSION -- B becomes somewhat IRRELEVANT. Will this reasoning also work to ELIMINATE B ?

You're right that B is irrelevant. If there were some risk of a person acquiring the disease directly from the mice, that particular risk isn't going to be impacted by the introduction of the uninfected species. If person X gets the disease from a tic bite and person Y gets the disease from playing with a mouse, we can still bring down the incidence of the disease by making sure person X isn't bitten by an infected tic. Moreover, the argument tells us directly: Lyme disease is caused by a bacterium transmitted to humans by deer ticks. We can't contradict a premise, so we have to accept that this is how Lyme disease is transmitted.

DavidG@VeritasPrep wrote:

Just a quick clarification reqd. This CR seems to be a CAUSAL ARGUMENT (If X then Y). Right ?

Typically a causal argument will involve an observed correlation: B seems to increase as A increases, therefore, A causes B. And you can weaken that argument by showing that, in fact, it's B that causes A, or there's some other underlying cause.

However, in this case, we have a proposed plan with a predicted outcome, so we wouldn't necessarily employ the same logic we'd use in an argument that involved an observed correlation.

Hi Dave,
While I can understand you here, just a quick question -

For a CR ARGUMENT employing If X then Y LOGIC, will it NOT be considered a CAUSAL ARGUMENT at its core, generally ?

Curious to know your thoughts!

RBBmba@2014 wrote:

DavidG@VeritasPrep wrote:

Just a quick clarification reqd. This CR seems to be a CAUSAL ARGUMENT (If X then Y). Right ?

Typically a causal argument will involve an observed correlation: B seems to increase as A increases, therefore, A causes B. And you can weaken that argument by showing that, in fact, it's B that causes A, or there's some other underlying cause.

However, in this case, we have a proposed plan with a predicted outcome, so we wouldn't necessarily employ the same logic we'd use in an argument that involved an observed correlation.

Hi Dave,
While I can understand you here, just a quick question -

For a CR ARGUMENT employing If X then Y LOGIC, will it NOT be considered a CAUSAL ARGUMENT at its core, generally ?

Curious to know your thoughts!

Well, first we'd want to differentiate between an observed relationship and one that we might predict. For example: Last year Company X raised its prices by 50%, and its profits went down. Therefore the increase in profits caused the decrease in profits. Here we have an observed correlation and we're trying to determine if one thing actually caused another.

We could also make an If-Then prediction. If a company raises its prices by 50%, then its profits will go down. Notice that in this case, we're making a general prediction about the future, rather than attempting to analyze a particular observation. It is true, however, that the prediction involves a causal element.

That said, I think of this type of causality as being a particular subset of If-then propositions. It's important to bear in mind that not all If-then statements predict traditional causal relationships.

A: If I run 10 miles, I will be tired. Here we have a traditional causal relationship. Running 10 miles would cause my tiredness.
B: If I am wet, it is raining outside. Well, it wouldn't make sense to say that my being wet caused it to rain. (Though you could reverse it to say that the rain caused me to be wet.)
C: If 'x' is a square, 'x' has four sides. It would be strange to claim that the fact that 'x' is a square caused it to have four sides. The four-sidedness is simply a property of squares.

This is all to say that If-Then statements can establish different kinds of relationships, causality among them, so you shouldn't treat all If-Then statements the same way you'd treat a classic correlation vs. causation argument.

DavidG@VeritasPrep wrote:

RBBmba@2014 wrote:Hi Dave,
While I can understand you here, just a quick question -

For a CR ARGUMENT employing If X then Y LOGIC, will it NOT be considered a CAUSAL ARGUMENT at its core, generally ?

Curious to know your thoughts!

Well, first we'd want to differentiate between an observed relationship and one that we might predict. For example: Last year Company X raised its prices by 50%, and its profits went down. Therefore the increase in PRICES caused the decrease in profits. Here we have an observed correlation and we're trying to determine if one thing actually caused another.

We could also make an If-Then prediction. If a company raises its prices by 50%, then its profits will go down. Notice that in this case, we're making a general prediction about the future, rather than attempting to analyze a particular observation. It is true, however, that the prediction involves a causal element.

That said, I think of this type of causality as being a particular subset of If-then propositions. It's important to bear in mind that not all If-then statements predict traditional causal relationships.

A: If I run 10 miles, I will be tired. Here we have a traditional causal relationship. Running 10 miles would cause my tiredness.
B: If I am wet, it is raining outside. Well, it wouldn't make sense to say that my being wet caused it to rain. (Though you could reverse it to say that the rain caused me to be wet.)
C: If 'x' is a square, 'x' has four sides. It would be strange to claim that the fact that 'x' is a square caused it to have four sides. The four-sidedness is simply a property of squares.

This is all to say that If-Then statements can establish different kinds of relationships, causality among them, so you shouldn't treat all If-Then statements the same way you'd treat a classic correlation vs. causation argument.

Hi Dave,
Thanks for the insights. That was really helpful... (Btw, I think, there should be a Typo-correction in your last post I've marked that in RED. Please amend accordingly.)

1. How we can quickly understand which If-Then is expressing a CAUSAL relation and which one is NOT ? (I mean, is there any EFFICIENT way to gauge this during test environment, apart from understanding the LOGIC of the ARGUMENT ?)

2. And from all these discussions, I got a small doubt that why the If-Then statement at hand is NOT expressing a CAUSAL relation ? Because it appears to me that this prediction -- if the population of these other species were increased, the number of ticks acquiring the bacterium would likely decline -- means increase in population of these other species will bring down/cause the decline in the number of ticks acquiring the bacterium. So, why it'd be wrong to tag it as a CAUSAL one ? (it's really confusing!)