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 Jonathan Evans
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Hi, Sophia,

Excellent question! Yes, you are correct, the statement in (A) could conceivably weaken the main conclusion; however, the question is which answer choice most weakens the argument. If you're faced with two possibilities such as this, try to zero-in on meaningful differences between the two options.

For instance, let's focus for example on strength of language in answer choice (A) versus that of answer choice (B). Answer choice (A) states that many normal weight babies are born to mothers who had inadequate prenatal care. Answer choice (B) states that hospitals routinely classify mothers of underweight babies as ex post facto recipients of inadequate prenatal care. Which of these terms, "many" or "routinely," is stronger? "Many" is a somewhat nebulous term: it could be several (like 40 or 50 out of 500); it could be most (like 300 out of 500); or it could be almost all (like 480 out of 500). In general I tend to lump "many" in with its pal "some," i.e. I treat both like "not none" but don't give them much more rope than that. "Routinely" on the other hand indicates a habitual, fixed program, something that reoccurs with such frequency that it is to some degree unremarkable. Thus, "routinely" is a far more powerful qualifier than is "many" and ipso facto makes (B) a more likely candidate.

As an aside, if I ever come across the word "many" in a strengthen or weaken answer choice, I tend to get very leery of that choice. It's kinda a perennial favorite wrong-answer-word. Not to say it will never appear in a correct answer. It may (and I strongly suspect it has!), but just be aware of what "many" actually means.

In addition, you could ask yourself, "So what if a lot of babies with normal birth weights are born to mothers who received inadequate prenatal care? Does this provide strong evidence against a possible causal link between inadequate prenatal care and lower birth weights?" It all depends on the relative frequency with which underweight vs normal weight babies are born to mothers who received inadequate prenatal care. It is certainly possible that, say, 80% of babies born to mothers who received inadequate prenatal care have normal birth weights. However, even granted the truth of answer choice (A), it is equally plausible that 90% of babies born to mothers who did receive adequate prenatal care have normal birth weights. Thus, even with answer choice (A), we do not have strong evidence against the possibility that inadequate prenatal care could correlate strongly (and perhaps causally) with underweight babies.

Answer choice (B) in contrast gives direct evidence to undermine this link, as you noted correctly. Thus, on its merits, answer choice (B) is a far stronger option and the best possibility when searching for what would most weaken this argument.

Thanks for the great question!
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I realize this is a sort of reductive approach to these types of questions. However, I did notice that the conclusion is a causal statement supported entirely by records (sort of like a study), which just happens to contain correlations.

While there are definitely correlations that are designed to support the argument, the correlations are contained within the records, which, as a whole, are used as the sole support for the conclusion.

A while back, I came across some advice which suggested that when a causal conclusion is supported solely by a study, then the answer choice will typically address the study, and this seemed to apply in this question, though I didn't realize it at the time.

The other part of the advice was that when a causal conclusion is supported solely by correlations, the error is most likely in regard to the correlations, which, depending on the question type (strengthen/weaken) means you should try to supply/block an alternate explanation or show that when cause appears effect appears or when cause appears effect doesn't appear.

I realize this isn't a hard and fast rule, but it's helped me a bit, so I just thought I'd mention it here.
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I'm still a bit stuck on why (C) isn't wrong--I think someone else mentioned this, but when I read the argument, I immediately started to think that there was some sort of link between the premature births and the adequate care, since both are correlated with low birth weight. I selected (C) because I thought that the premature birth could potentially be the "cause" rather than the adequate care. Is this wrong because it talks about low birth weight when the conclusion talks about decreased low birth weight? I've read through all the responses about why (C) is wrong, but they just don't seem to answer this.
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Hi Olivia!

Alternate causes are a great way to weaken causal arguments, but answer choice (C) does not present an alternate cause. We already know from the premises in the stimulus that premature babies are more likely to have a low birth weight than babies that are not premature. So drawing a connection between low birth weight and being born premature has no effect on this argument because, essentially, that correlation is already right there in the argument. It doesn't present an alternate cause of the low birth weight either because these causes are not mutually exclusive. It's entirely possible within the bounds of the argument that adequate prenatal care reduces the risk of premature birth which reduces the risk of low birth weight (which is why you felt like there was probably a link between adequate care and premature births!).

So if answer choice (C) is true and "hospital records indicate that low birth weight babies were routinely classified as having been born prematurely," would that attack the argument that adequate prenatal care decreases the risk of low birth weight? No, because whether or not low birth weight babies are classified as being born prematurely, prenatal care could still be affecting birth weight.

Hope this helps!


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