Medical researcher: As expected, records covering the last four

Records show that premature babies were more likely to have low birth weight than normal babies.
Records also show that women who got adequate prenatal care were less likely to have low birth weight babies (than women who did not get enough care)

Conclusion: Adequate prenatal care significantly decreases the risk of low birth weight babies.

Let's use some variables to see the connections clearly:

Records show A (premature) leads to X (low weight).
Records also show B (inadequate care) leads to X and 'not B' leads to 'not X'.
We conclude that 'not B' will lead to 'not X'.

We need to weaken the argument.
The records show that women who get adequate care were less likely to have low weight babies. From this we are concluding that adequate care decreases the risk of low weight babies. How do we weaken our conclusion? By somehow establishing that records do not reflect reality.

A. The hospital records indicate that many babies that are born with normal birth weights are born to mothers who had inadequate prenatal care.

Irrelevant. This just says that with inadequate care too, normal babies CAN BE born. This doesn't change that with inadequate care, it is MORE LIKLEY to have low weight babies.

B. Mothers giving birth prematurely are routinely classified by hospitals as having received inadequate prenatal care when the record of that care is not available.

This says that A is often classified as B. That 'premature birth' is often classified as 'inadequate care'. This muddies the link between B and X. The link may be between A and X. Since A is often classified as B in reports, that could explain the relation between B and X. Hence report classification may not represent an actual link between care and low birth weight. This does weaken our conclusion.

C. The hospital records indicate that low birth weight babies were routinely classified as having been born prematurely.

This says that X is classified as A (so instead of A leading to X, X may be classified as A). In any case, our conclusion deals with relation of B with X. This is irrelevant.

D. Some babies not born prematurely, whose mothers received adequate prenatal care, have low birth weights.

This says that even with 'not A' and 'not B', X could happen. It doesn't impact us. We are talking about probabilities. With A, there is higher risk of X. With B there is higher risk of X. X could happen with not A and not B too. It doesn't worry us.

E. Women who receive adequate prenatal care are less likely to give birth prematurely than are women who do not receive adequate prenatal care.

It says 'not B' leads to 'not A'. This helps our argument.
Since A leads to X, not A is likely to lead to not X. Hence, indirectly too, 'not B' does seem to lead to 'not X'.

Answer (B)

OFFICIAL EXPLANATION

The correct answer choice is (B).

The premises contain correlations, and the conclusion makes a causal claim: PC = adequate prenatal care, DR = decrease risk of low birth weight babies. The question stem asks you to weaken the argument, and the correct answer falls into one of the five basic methods for weakening a causal argument.

Answer choice (A): The conclusion specifically states that mothers who had received adequate prenatal care were less likely to have low birth weight babies than mothers who had received inadequate prenatal care. Thus, although mothers who received inadequate prenatal care have a higher likelihood of having low birth weight babies, this likelihood still allows for many babies to be born of normal weight. In a later chapter we will explore the ways the GMAT uses numbers and statistics to confuse test takers, but for now, consider this analogy: The Detroit Tigers are more likely to lose a baseball game than any other team, but even so, they can still win a number of games. In the same way, the aforementioned mothers may be more likely to have low birth weight babies, but they can still give birth to babies of normal weight. Hence, answer choice (A) does not attack the argument.

Answer choice (B): This is the correct answer. The answer choice falls into the category of “Showing a statistical problem exists with the data used to make the causal statement.” By indicating that all mothers without prenatal care records are automatically classified as mothers receiving inadequate prenatal care, the answer undermines the relationship in the argument because the data used to make the conclusion is unreliable.

Answer choice (C): The conclusion is about low birth weight babies, not premature babies. Even if low birth weight babies were routinely classified as premature, that would not affect the conclusion.

Answer choice (D): Similar to answer choice (A), the likelihoods discussed in the stimulus allow for this possibility. Hence, this answer cannot hurt the argument.

Answer choice (E): If anything, this answer strengthens the argument since it shows that adequate prenatal care has a powerful positive effect.
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I'll go with B.
Since most of the premature babies have low birth weight, routinely tagging them as babies whose mothers received inadequate prenatal care will inflate the proportion of low-birth-weight babies to mothers who received inadequate prenatal care and give us a wrong impression of the effect of inadequate prenatal care on low-birth-weight deliveries.

Question Type : WEAKENER

Conclusion :- Adequate parental care => reduce risk of low wight birth babies.

What if data is skewed in favour of above conclusion. So let's say whenever there is any low weight birth babies, we will say OH! THEY HAVE NOT PROVIDED PROPER CARE IN PREGNANCY.

This is what B is doing. Mothers giving birth prematurely are routinely classified by hospitals as having received inadequate prenatal care when the record of that care is not available. => whenever there is any mother give premature birth, if we don't know what kind of care provided, we will put into the record of inadequate prenatal care.

Due to this reverse engineering, Adequate parental care => reduce risk of low wight birth babies. will be shown as correct but it is not correct relationship.

so B IS RIGHT ANSWER.

Lets focus on the conclusion,,
it relates the adequate prenatal care to decreasing risk of low birth weight babies..
A: the argument doesnt say only adequate pre natal care reduces low birth weight.. WRONG
B: address our conclusion, if the record is not availabe and classifying improperly will inflate the records.. RIGHT
C: doesnt address the conclusion
D: the conclusion says SIGNIFICANTLY... if the conclusion used the word ONLY,, this is right,,, WRONG
E: Irrelavant

ANS B

Medical researcher: As expected, records covering the last four years of ten major hospitals indicate that babies born prematurely were more likely to have low birth weights and to suffer from health problems than were babies not born prematurely. These records also indicate that mothers who had received adequate prenatal care were less likely to have low birth weight babies than were mothers who had received inadequate prenatal care. Adequate prenatal care, therefore, significantly decreases the risk of low birth weight babies. Which one of the following, if true, most weakens the medical researcher’s argument?

A. The hospital records indicate that many babies that are born with normal birth weights are born to mothers who had inadequate prenatal care.
It is not 100% that adequate parental care will lead to normal birth weight. There will always be exceptions.

B. Mothers giving birth prematurely are routinely classified by hospitals as having received inadequate prenatal care when the record of that care is not available.
Correct. It raises question on the statistics. If the records are not proper then the conclusion doesn't hold.

C. The hospital records indicate that low birth weight babies were routinely classified as having been born prematurely.
It is not 100% that adequate parental care will lead to normal birth weight. There will always be exceptions.

D. Some babies not born prematurely, whose mothers received adequate prenatal care, have low birth weights.
It is not 100% that adequate parental care will lead to normal birth weight. There will always be exceptions.

E. Women who receive adequate prenatal care are less likely to give birth prematurely than are women who do not receive adequate prenatal care.
There is no new information. This is already present in the passage

I could narrow it down to A vs B but I'm unable to understand why A is incorrect !! Whats the issue with A here ?

Hi Anuj,

This is a Magoosh explanation from Beat The GMAT:

Let's say (A) does make a sufficient dent to the question - it still doesn't answer the question:

"Which one of the following, if true, most weakens the medical researcher’s argument."

(B) on the other hand completely weakens (vs. dents) the conclusion. Mothers who give birth to premature babies, but who do not have record have that care, are automatically grouped in the "inadequate care" category, thus conflating low birth weight of premature babies with all babies receiving inadequate care.

Returning to (A), it simply states that many normal birth weight babies received inadequate care. That doesn't mean that the inadequate care group doesn't have a lower risk than the adequate care group. The latter group could have had a greater percentage of babies born at a normal birth weight.

So (B) is the clear cut answer.


These are from above from people on this forum:

Gmatexam439's:
A. The hospital records indicate that many babies that are born with normal birth weights are born to mothers who had inadequate prenatal care.
It is not 100% that adequate parental care will lead to normal birth weight. There will always be exceptions.

B. Mothers giving birth prematurely are routinely classified by hospitals as having received inadequate prenatal care when the record of that care is not available.
Correct. It raises question on the statistics. If the records are not proper then the conclusion doesn't hold.

Moshu's:
A: the argument doesnt say only adequate pre natal care reduces low birth weight.. WRONG
B: address our conclusion, if the record is not available and classifying improperly will inflate the records.. RIGHT

Does this help you out?
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At first glance, this argument appears to be mistaking a correlation with a cause and effect relationship. However, the conclusion is that adequate prenatal care "reduces your risk" of low birth weight - that's different than saying that inadequate prenatal care causes low birth weight. The real problem must be in the statistics themselves. Otherwise, there wouldn't be much of an issue with the argument.

We are asked to find an answer choice that weakens the argument. Many of these are close, but turn out to be consistent with the argument.

(A) is tempting but consistent with the argument. The argument never claims that everyone with inadequate prenatal care would be born with low birth weight.
(B) undermines the argument by suggesting that how they're measuring the phenomena could be flawed, and that one characteristic could be construed as both having inadequate care and low birth weight. This would misconstrue the relationship and likelihood that those two phenomena overlap.
(C) relates being born premature and having a low birth rate. The conclusion is about prenatal care and birth weight, so misconstruing the relationship between these two factors would not undermine the conclusion.
(D) is consistent the argument's conclusion for the same reason that answer choice (A) is consistent - the argument never claims that no one with adequate prenatal care would be born with a low birth weight.
(E) is wrong for the same reason that answer choice (C) is wrong. It's relating premature birth with, adequate prenatal care, but premature birth is not related to the conclusion.

Medical researcher: As expected, records covering the last four years of ten major hospitals indicate that babies born prematurely were more likely to have low birth weights and to suffer from health problems than were babies not born prematurely. These records also indicate that mothers who had received adequate prenatal care were less likely to have low birth weight babies than were mothers who had received inadequate prenatal care. Adequate prenatal care, therefore, significantly decreases the risk of low birth weight babies.

Which one of the following, if true, most weakens the medical researcher’s argument?

A. The hospital records indicate that many babies that are born with normal birth weights are born to mothers who had inadequate prenatal care.

B. Mothers giving birth prematurely are routinely classified by hospitals as having received inadequate prenatal care when the record of that care is not available.

C. The hospital records indicate that low birth weight babies were routinely classified as having been born prematurely.

D. Some babies not born prematurely, whose mothers received adequate prenatal care, have low birth weights.

E. Women who receive adequate prenatal care are less likely to give birth prematurely than are women who do not receive adequate prenatal care.

There's always a good amount of doubt when it comes to passage that deal with data-keeping in the form of surveys or in the form of a study/research or in the form of medical records being kept in hospitals as in this case.

Two indication are given by the records in this passage:
1. That that babies born prematurely were more likely to have low birth weights and to suffer from health problems than were babies not born prematurely.
2. That mothers who had received adequate prenatal care were less likely to have low birth weight babies than were mothers who had received inadequate prenatal care

Then there's the conclusion that adequate prenatal care significantly decreases the risk of low birth weight babies. Thus, it suggests that there's a process of flow from prenatal care to its impact on birth weight of babies to babies suffering form health issues or not.
Note: It is not conclusive that prenatal care helps in babies not being born prematurely i.e. it may or may not be the case. However, it looks likes so - a danger sign.
Hence we need to be very careful whether to look for prematurity of births or not because that is not what around which the passage revolves.

I have highlighted text in each option with which it suffers from or not.
A is logical opposite to what we are looking, at best irrelevant.
C has not covered prenatal care aspect.
D has only issue about the scale of 'some'. Had conclusion not used the word 'significantly' this options would have been hard to eliminate.
E like - in opposite manner - C takes care of prenatal care but not about low birth weights.
B touches upon prematurity aspect but it nicely related to prenatal care and low birth weights.

Answer B.
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Best example of why it is MUST to stick to the argument from which conclusion is drawn:

Below is the explanation by Manhattan folk:
Once you've read an argument and found the conclusion, I recommend doing the following things.

[b]1. Say the Conclusion, and then ask "how come? how do we know? what's the support?"
Adequate prenatal makes you less at risk of low birth wt babies.
how do we know?

[b]2. Find the Supporting reason(s).
Because there's a correlation between adequate prenatal care and low birth weight.

Does the correlation between born prematurely and low birth weight matter?

Not yet. We might be anticipating that they're inserting this filler for the sake of using it later or just for the sake of making more concepts available for trap answers.

But given that 1st sentence and 2nd sentence are each a correlation, we obviously care more about the 2nd one, since THAT correlation connects the cause/effect in the author's conclusion.

We should just prephrase this like we do ALL causal conclusions:
1. Is there some OTHER WAY to explain the Evidence?
2. How PLAUSIBLE is the Conclusion?

In the terms of this argument,
1. Is there some OTHER WAY to explain why there's a correlation between adequate prenatal and low birth weight?

or

2. What would decrease the plausibility that prenatal care has an effect on the birth weight of the baby?

(B) is correct because it performs the function of #1.

It suggests that the reason prenatal and low birth weight are correlated is NOT because prenatal actually causally affects birth weight, but rather because being born premature leads to both low birth weight and to being classified as "inadequate prenatal care".