Logical reasoning PrepTest 130 · Section 3 · Question 11

Incorrect. Being a vegetarian isn't tied to any health benefits or risks, so it's unclear what effect this has on the argument. (Vegetarians aren't inherently more healthy than others, so we can't assume that connection without it being established.)

Incorrect. If this group did have a diet that was otherwise conducive to heart disease, and they still saw a rate 30% lower than those who don't eat fish, then something about the fish must really work. Negating this answer strengthens the argument, so it can't be necessary for it to hold.

Incorrect. Similar to (A), we can't bring in outside information. We don't know the effect of eating red meat on heart disease, so we can't say that this answer factors in.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Necessary Premise

Stimulus Summary:
Scientists: O3 lowers blood cholesterol and improves health.

Now: Supported! A study shows that middle-aged people who eat fish twice a week have a much lower risk of heart disease.

Answer Anticipation:
This argument starts with what scientists have "long thought," which usually introduces an opposing point that the author pivots away from. However, this question breaks that pattern and instead goes on to support that view with a new study. And when there are studies, there are frequently sampling flaws, and correlation/causation flaws.

Is there a correlation/causation flaw here? In the study, middle-aged people who ate fish twice a week had a much lower risk of heart disease. This is a correlation, and the view of the scientists is a causal one, so this argument jumps from correlation to causation.

What about the sample? While this group did eat fish twice a week (which surely counts as a modest amount), there's no indication that other factors were controlled for. If this sample is different from other middle-aged people in some other key way, then it doesn't support the conclusion.

Since both flaws overlap in one key area—the possibility that this group has another feature which explains their lower level of heart disease other than the fish consumption—we should look for an answer that addresses that. Since this is a Strengthen with Necessary Premise question, the correct answer could either rule out all potential alternative causes, or a single one, as the argument needs to eliminate each potential alternative explanation to reach the one it does in the conclusion.

Answer Explanation:
Unlike (A) or (C) (or (E), when we get to it), this answer ties a possible alternative factor into heart disease ("cardiorespiratory health"). If the group that ate fish a few times a week was also significantly more likely to engage in activities that promote heart health, then that could be the reason for their lower rate of heart disease, undermining the view of the scientists that it's the O3 in fish causing that effect.

Key Takeaway:
Don't bring in outside assumptions! Several of these answers raised assumed health connections that may be widely believed, but they're not inherently true. The LSAT will let you make connections when they're based on the definitions of the words, but not when the underlying concepts aren't inherently linked.

Incorrect. Similar to (A), we can't bring in outside information—having a sedentary job isn't established as being linked to health issues, so we can't make that jump. Also, note the slight difference between this answer and answer (D)—this answer says "no more likely", whereas (D) says "not significantly more likely". The latter is more likely to be correct in a Strengthen with Necessary Premise question since the likelihood being .0000000001% higher in one case over another would technically be more likely, but probably wouldn't throw off the representativeness of a sample.