#18 - Journalist: Scientists took blood samples from two

[Administrator]

Complete Question Explanation

Flaw in the Reasoning—CE. The correct answer choice is (E)

The journalist in this stimulus describes a scientific study in which scientists took blood samples
from two groups of volunteers, and is careful to tell us that the two groups were large and diverse.
All of the members of one group said that they enjoyed eating vegetables. All of the members of the
second group said that they disliked vegetables. Analysis of the blood samples taken from the second
group showed that all of the members of that group had the gene XRV2G in common. Based on this
evidence, the author concludes that “a dislike of vegetables is, at least in some cases, genetically
determined.”

The journalist’s causal conclusion is flawed, because the only evidence offered in support of it was
the correlation between the presence of XRV2G in the blood of the members of the second group
and that group’s dislike of vegetables. Even assuming that the members of the second group not only
dislike vegetables but also actually refrain from eating them—which is not necessarily the case—it
may be that not eating enough vegetables leads to the presence of XRV2G in the blood.
This is a Flaw question. Our prephrase is that the correct answer choice will likely reference the
journalist’s flawed use of causal reasoning.

Answer choice (A): In order for this answer choice to be correct, it must have been the case that the
journalist’s conclusion referenced all human traits, which it did not do.

Answer choice (B): This answer choice is incorrect, because the journalist told us that the two
groups of volunteers were both large and diverse.

Answer choice (C): This answer choice is attractive to many because it explicitly refers to
causal reasoning. However, it is incorrect because the journalist did not take evidence of a causal
relationship and reach a causal conclusion. Instead, the journalist’s evidence dealt with a correlation.

Answer choice (D): We cannot say that the conclusion overlooked this possibility, because the
conclusion referred to genetic determination generally, and did not specifically reference XRV2G.

Answer choice (E): This is the correct answer choice, because it addresses the author’s causal
conclusion. Remember that when a stimulus author on the LSAT reaches a causal conclusion, the
author is saying that every time the cause is present, then the effect is present, and vice versa. The
journalist did not examine blood samples of the first group, those folks who say they like vegetables.
By concluding that there is a causal relationship between the gene and a dislike of vegetables, the
author is simultaneously saying that if a person likes vegetables then they would not have that gene.

[MikeRov25]

Is E the answer because the stim does not specifically state that the group that enjoyed eating vegetables had their blood tested?

[MikeRov25]

also what kind of falacious reasoning is this?

[Adam Tyson]

Hey there Mike, let me see if I can help. I think you are most of the way there in your analysis, but it goes beyond just that the other group's blood wasn't tested (because it might have been and we just weren't told about the results). The problem is that we don't know the results of any blood work on the other group, and it might be that they, too, had that same gene.

I think we could categorize this flaw a couple of ways at least. First and foremost, it's a causal flaw - the author has attributed a causal relationship to a correlation (the gene correlates to disliking veggies), but he has failed to account for the possibility that the cause may be present in the other group that does not display the effect.

I think we could also look at this as an evidence error, because there is a general lack of relevant evidence. So what if they had that gene in common - couldn't any number of other things also matter?

The causal approach looks strongest to me, because even calling it an evidence flaw involves us acknowledging that the missing evidence is about possible alternate causes or cause without effect.

Take a look and see if that makes sense to you. Meanwhile, keep pounding!

[pavalos5777]

Hello,

I took answer choice C to indicate that the XRV2G gene could be present without the corresponding dislike for vegetables that the journalist is asserting.

Although I narrowed this down to C and E, I ultimately went with C. Can you please provide further explanation for C being incorrect?

Much appreciated,
Pierre

[Adam Tyson]

Thanks for the question, Pierre! There are two problems that I see with answer C here, and the first one is a big one - the author actually did NOT overlook that possibility (that some folks may dislike veggies even if they don't have that particular gene). He allows for that possibility by limiting his conclusion with "at least in some cases". He's allowing for the possibility that there can be other causes even when the gene is absent, not overlooking that possibility.

The other problem with answer C is that the answer itself takes for granted what the author is trying to prove - that the gene causes a dislike of veggies. This is the lesser of the two problems, in my opinion, as the first one kills the answer completely.

Since our author didn't overlook the possibility of alternate causes for disliking veggies, answer C doesn't describe what really went wrong (which is making a causal claim in the first place based on insufficient data).

I hope that helps!

[kozimbod]

Hello,

I got this question right, but did not have 100% confidence in the answer when I was doing it, so I decided to go back and review. Is it necessary for the journalist to explicitly state that he/she analyzed the blood samples from the group that liked vegetables, and upon analyzing, he/she did not discover the XRV2G gene? Or is the mere fact that the journalist does not mention this grounds enough to attack the argument for making this underlying assumption? Considering the goal is to attack the argument itself (the words used in the stimulus) and not whatever the case may actually be with the studies, I guess this does provide grounds enough to attack the flaw? Sorry if that is worded in a confusing way, but I hope you know what I mean.

Thanks!
Danny

[Luke Haqq]

Hi Danny!

I'll try responding to your question in two parts. First, you ask,

Or is the mere fact that the journalist does not mention this [about the group that liked vegetables] grounds enough to attack the argument for making this underlying assumption?

Yes, the fact that this is not mentioned could potentially be a point of attack in seeking to locate a flaw. Since we have to stick to what is in the stimulus alone, that means we're left in the dark as to information about the genetics of this group (specifically the presence or absence of the XRV2G gene).

Second, you asked whether it is "necessary" for the journalist to comment about findings from the group that liked vegetables. This only becomes necessary by virtue of the conclusion that the author reaches--we don't know if the findings of the XRV2G gene in the group that disliked vegetables shows a genetic basis for disliking vegetables. We don't know this because it could be the case that all the people in the group that liked vegetables could have had this gene as well. The stimulus relies on too little evidence to reach the conclusion that it reaches. For the author to have reached that conclusion, it would have been necessary to know whether the XRV2G gene was also present in the group that liked vegetables (in which case, its presence among the group that disliked vegetables would no longer count as evidence for a genetic basis to disliking vegetables).