#8 - Monarch butterflies must contend with single-celled

[Administrator]

Please post your questions below!

[Iqranaqvi]

Could you please clarify as to why C is incorrect and D is correct?

[Robert Carroll]

Iqranaqvi,

The author concludes that a difference in parasitic infection rates between migrating and non-migrating butterflies is due to migration. Why couldn't it be the other way around? In fact, the stimulus even says that infected butterflies can have deformities that interfere with flight. It makes at least as much sense as the author's conclusion to think that instead the butterflies that couldn't fly right didn't migrate, so the difference in infection rates is the cause of differences in migration rather than vice versa. This precisely is answer choice (D).

The size of the population does not affect the percentage infected, so answer choice (C) is itself confusing numbers and percentages. Percentages are relevant here, and it was not a flaw in the reasoning to stick with percentages. There is no need to provide additional information about raw numbers.

Robert Carroll

[lanereuden]

The question's conclusion says, "this shows that migrating allows monarch butterflies to avoid these parasites." To me, this means that the reason that these butterflies migrate is to avoid parasites.
Thus, when I read the answer choice "monarch butterflies infected with parasites are typically unable to migrate," this answer choice did not seem to contain a flaw, but instead, it provided further reason as to why migration is important--to get away from being infected in the first place. Please explain the deficiency in my understanding if at all possible.
For the record, when I choose the answer I did (A), I assumed that if they were "unable to detect which areas are free from parasites," then it is no longer important for them to migrate because it would mean that they would have no better odds elsewhere of avoiding the parasites...and so, this would be a flaw in the argument.

[James Finch]

Hi Lane,

This is a causal stimulus (migration causes fewer parasites), so we should approach this flaw question similar to that of a Strengthen or Weaken one, and identify the potential problems with the posited causal relation given the stated premises. Given the way that the question stem is worded, we'll be looking for something very close to a Weaken answer here.

There are 4 major ways to weaken causal conclusion:

Identify a possible alternate cause;

Show the either the cause present without the effect, or the effect present without the cause;

Show mere correlation instead of causation;

And finally, show the possibility of reverse causation (the stated cause is actually an effect of the stated effect).

It's difficult to come up with a plausible reverse causation scenario, because of the chronological element involved in causal reasoning: the cause has to come before the effect. So I always test whether reverse causation is possible when Prephrasing a Weaken or causal Flaw question, as the times that reverse causation is possible is tends to be the correct answer.

Here, reverse causation is absolutely possible and almost obvious in hindsight; butterflies infected with parasites would be far less likely to be able to migrate, as the parasites interfere with their ability to fly, and so migrating butterflies would have far less likelihood of having the parasites than non-migratory ones. Answer choice (D) reflects this possibility, and is the correct answer, while (A) doesn't reflect an actual flaw in the reasoning, as we are comparing only the rates of parasite infection between non-migrating butterflies and migrating ones, not where they choose to migrate to.

Hope this clears things up!

[lanereuden]

Hi James,

Thanks for the reply. In other cases, when you get a weaken question....are you just looking for those 4 (cause-effect) scenarios typically? Or are there more considerations you have to make/scenarios to consider?

[lanereuden]

Also, would the analogous case I present below make contain a similar flaw, or would adjustments need to be made to the argument below so that it possesses the same flaw as the one presented in this question?

P1: for those who have xyz condition and did not take this drug, as many as 95% are heavily infected with the condition
P2: for those who have xyz condition and did take the drug, less than 15% are infected with the condition
Conclusion: this fact pattern shows that taking this drug helps you not get infected
Problem: it overlooks the possibility that those infected typically cannot take the drug

[Adam Tyson]

Thanks for the question, lanereuden. The 4 approaches James mentioned only apply to causal reasoning questions, and while those are common in weaken questions, there are other types of arguments that you will be asked to weaken. You may be asked to weaken an argument that is based on an analogy, which you would do by suggesting that the two things being compared are insufficiently similar. Or, if the argument is based on a false dilemma, you might weaken it by pointing out that there are other options available. There are many more examples of non-causal arguments that you might encounter, and the 4 causal approaches James listed would not apply to them.

Also, regarding causal reasoning, I believe that James left one common weakness out of the discussion, and that is related to reliance on questionable data. That is, if the causal conclusion is based on studies, experiments, surveys, or any assumptions about data, an answer that raises doubts about the accuracy or reliability of that data would also weaken the argument.

Your analogy looks okay to me, assuming that "xyz condition" and the condition that some of them are infected with are not the same condition. Maybe more like this, for clarity:

P1: for those who have xyz condition and did not take this drug, as many as 95% are heavily infected with bacteria Q
P2: for those who have xyz condition and did take the drug, less than 15% are infected with bacteria Q
Conclusion: this fact pattern shows that taking this drug helps you not get infected with bacteria Q
Problem: it overlooks the possibility that those infected with bacteria Q typically cannot take the drug

That more clearly sets up the same kind of possible reversed cause and effect that we also had in this question.

Good work, you've got this!

[lina2020]

Hi PowerScore,

I confidently chose C as my answer and even after reading through the explanations on this forum, I'm having trouble understanding why D is correct. For quick reference, I pasted the question below as it typically takes a couple of days to get a response.

My thought process with C is that there is a numbers/percentages flaw in this argument --> although less than 15 PERCENT of those in migrating populations are infected, perhaps the ACTUAL NUMBER of those migrating are much higher than those not migrating, in which case it would expose a flaw on the causal conclusion "that migrating allow monarch butterflies to avoid these parasites" because in fact there could be a larger number of those migrating affected than those non-migrating. Would you please explain in detail what I may be missing here? I somewhat understand the reasoning for D being reverse causation but I feel like my explanation could possibly indicate a second flaw with this argument. Any insight on answers C and D is appreciated!

Also, would you mind pointing me in the direction of 2-3 other similar reverse causation LR questions that I could look at to better understand this concept? I'm a current PowerScore student so if you mention the PrepTest number and year, I can locate the question and answers. Thank you!

Stimulus:
Monarch butterflies must contend with single-celled parasites that can cause deformities that interfere with their flight. In populations of monarch butterflies that have not migrated, as many as 95 percent are heavily infected by the parasites, while less than 15 percent of those in migrating populations are infected. This shows that migrating allows monarch butterflies to avoid these parasites.

C. populations of monarch butterflies that have not migrated are much larger than migrating populations
D. monarch butterflies infected with parasites are typically unable to migrate

[KoenXin]

Hi PowerScore,

I confidently chose C as my answer and even after reading through the explanations on this forum, I'm having trouble understanding why D is correct. For quick reference, I pasted the question below as it typically takes a couple of days to get a response.

My thought process with C is that there are a numbers/percentages flaw in this argument --> although less than 15 PERCENT of those in migrating populations are infected, perhaps the ACTUAL NUMBER of those migrating are much higher than those not migrating, in which case it would expose a flaw on the causal conclusion "that migrating allow monarch butterflies to avoid these parasites" because in fact there could be a larger number of those migrating affected than those non-migrating. Would you please explain in detail what I may be missing here? I somewhat understand the reasoning for D being reverse causation but I feel like my explanation could possibly indicate a second flaw with this argument. Any insight on answers C and D is appreciated!

Also, would you mind pointing me in the direction of 2-3 other similar reverse causation LR questions that I could look at to better understand this concept? I'm a current PowerScore student so if you mention the PrepTest number and year, I can locate the question and answers. Thank you!

Stimulus:
Monarch butterflies must contend with single-celled parasites that can cause deformities that interfere with their flight. In populations of monarch butterflies that have not migrated, as many as 95 percent are heavily infected by the parasites, while less than 15 percent of those in migrating populations are infected. This shows that migrating allows monarch butterflies to avoid these parasites.

C. populations of monarch butterflies that have not migrated are much larger than migrating populations
D. monarch butterflies infected with parasites are typically unable to migrate

I know I'm responding almost 2 months after this post, but hopefully this can be helpful for anyone with similar reasoning. I can see how someone can fall into this trap.

The reason C doesn't work is that the population size doesn't affect the argument like you're thinking. If the stimulus had used just the numbers in both of the moth groups, then the answer choice would be a lot more attractive, but ultimately its about percentages.


We will use the argument's reasoning for this analogy too so it makes more sense. If 95% of group A (who doesn't own a blue car) is infected with a virus, and 15% of group B (who do own a blue car) is, and I conclude that group B doesn't get infected as much because they drive blue cars, you'd probably tell me I'm taking crazy pills and my conclusion makes no sense, regardless of what numbers I'm using for those groups. Hopefully, you can see the analogy to the argument at hand.

Telling me that 19 people in A (who don't own blue cars) got infected, but 15 people in B (who do own blue cars) got infected, therefore doing X activity explains why B is infected less isn't a great argument, and it's lacking any additional support. If you responded to my analogy above with, "Well, what if there are more people who don't drive blue cars than those who do", you wouldn't be pointing out the error in the conclusion that is too strong, you're suggesting the size of the groups is an important factor and that there is possibly some truth to the stimulus argument. Rather, you should be attacking support for the claim that the specific activity of migrating lets them avoid the parasites.

Now if you replied to the argument, "Owning a blue car is irrelevant to whether they get sick or not, what if the only people who can drive blue cars are super rich people with lots of money to afford a vaccine/treatment in the first place", you'll see it's a better way of attacking the reasoning, and ultimately what the flaw is. Seeing a very obvious causal argument such as this one should be setting off alarms in your head to hone in on an answer choice that reflects that the causality stated is for another reason, or that there is only a correlation, or even reverse causation (which is what D is doing)