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Isn't answer A out of scope because the stimulus argues that switching to IPV would cut down on vaccination-caused polio? I don't think the argument cares about any increase in natural polio; the stimulus maintains only that we can cut down on vaccination caused polio by switching to IPV.

When I did the question I thought that while IPV may very well lead to more natural polio, this is irrelevant because the argument focuses on cutting down vaccination-caused polio.

Thus I chose B because it demonstrates that OPV is not responsible for polio in children. Rather, children are getting polio from the vaccine because they have weak immune systems, and they would get polio regardless of whether OPV or IPV was used (weakening the argument).

Can somebody please explain why A is better than B? Thanks!

yea i already read through Manhattan. none of the posts address the issue i raise, which is that the conclusion ignores natural polio and only states that IPV would result in less cases of vaccine-caused polio

The issue is that it says that natural occurring polio cases don't occur, they are just a product of the vaccine. So even if IPV leads to half as many vaccine caused cases of polio, if this leads to more natural occurring cases of the disease then this weakens the argument. The premise is that ipv causes half as many cases as OPV---> IPV should be the main vaccine. But if the switch caused other types of polio not included in the reasoning, then this weakens the reasoning.

The issue is that it says that natural occurring polio cases don't occur, they are just a product of the vaccine. So even if IPV leads to half as many vaccine caused cases of polio, if this leads to more natural occurring cases of the disease then this weakens the argument. The premise is that ipv causes half as many cases as OPV---> IPV should be the main vaccine. But if the switch caused other types of polio not included in the reasoning, then this weakens the reasoning.

Correct. And that's essentially what Manhattan said:

"It's easy to read this piece of evidence and conclude that it makes sense to switch to the apparently safer IPV vaccine. The problem with this reasoning is that while IPV may cause fewer cases of polio, it may allow a significant number of naturally occurring cases of polio. So, overall, IPV could lead to there being an overall increase in the total number of cases of polio.

(A) weakens the argument by reminding us that the IPV vaccine could lead to increased naturally occurring cases of polio and so while there would be a reduction in vaccination-caused cases, there would still be an overall increase in the total number of cases of polio."

I think I may see the problem.

Walterwhite, when you say:

Isn't answer A out of scope because the stimulus argues that switching to IPV would cut down on vaccination-caused polio? I don't think the argument cares about any increase in natural polio; the stimulus maintains only that we can cut down on vaccination caused polio by switching to IPV.

...you are not distinguishing between the premises of the argument and it's conclusion. You're right that the premises seem oriented toward the vaccination-caused polio, but the conclusion is an altogether different animal. The conclusion is "Clearly it is time to switch from OPV to IPV." The conclusion says nothing at all about the incidence of polio, vaccination-caused OR naturally occurring.

Therefore, anything that affects whether we should or should not switch from OPV to IPV, for any good reason, will be in scope for this argument. In fact, we could have weakened this argument with an answer that said that IPV caused more cancer than OPV - that would still be 100% in scope, as it would undermine the leap to the conclusion that "we should switch."

Any bad result from IPV as it compares to OPV will weaken the argument that we should switch. Since (A) gives something bad (more natural polio with IPV than OPV), it does exactly that.

As for (B), the premises clearly state that IPV would give us only half the vaccine-caused polio cases that OPV does. We can't refute that. And (B) is referring specifically to "cases of polio caused by OPV." Putting those together, the correlation with immunodeficiency simply doesn't change the fact that IPV will cut the vaccine-caused polio numbers in half. (Also note that this answer NEVER says that the immunodeficiency caused the polio, but even if it did, it would have done so in conjuction with the OPV.)

The most important issue here is that you are reading things into the conclusion that weren't said - specifically, you are reading the conclusion to be about vaccine-caused polio, when in fact it is only saying "we should switch from OPV to IPV."

Thoughts?

After going over this question I screwed up question 14 of section 3 on this same prep test.

I thought that choice B was attractive because allergic reactions seems to weaken the argument in the same way choice A weakens the argument in question 19. It didn't occur to me that choice B is completely out of scope and an obvious incorrect answer choice

After looking at question 14 again however I realize it was really easy and I messed it up because I was still thinking about the polio question. I'm really in a slump with weaken questions :/