LSAT 149 | Section 1 | Logical Reasoning: Q4

LR Question 4 Explanation

QUESTION TEXT: A survey published in a leading medical journal…

QUESTION TYPE: Flawed Reasoning

CONCLUSION: Aerobic exercise really helps people’s health.

REASONING: Aerobic exercise lowers the risk of lung disease.

ANALYSIS: This argument makes two flaws:

• It presents a correlation between lung disease prevention and aerobics, and treats it as causation.
• It takes evidence about a specific condition (“lung disease”) and treats it as evidence about health in general. Health is much broader than lung disease.

Either of these could have been the correct answer. The right answer uses the first.

One answer is a trap if you prephrased only the second. Watch out for this: LSAC is getting craftier. Answer D uses the terms from the second flaw, but it doesn’t have the same meaning. You can’t just skim for a prephrase, you have to actually make sure the answer says the right thing too.

Note: You might have thought this argument did show causation. The journal said “the more frequently” people did aerobics, the less they got lung disease? Isn’t that causation, because it applied at every level? Nope. It’s still just correlation: correlation means two things increase together. For causation you need some kind of mechanism showing a cause or at least a statement that one does cause the other.

___________

1. This is….a good idea? It isn’t a flaw!
2. Not so. The author says “since other surveys have confirmed….” So it’s more than just a single journal.
3. CORRECT. This is valid. We only have a correlation between aerobic exercise and improvements in lung health. It could be that some other factors accounts for the improvement. i.e. maybe people who do aerobics tend to smoke less.

4. The argument didn’t say this. Interpreted literally, this answer is insane, and you have to interpret LSAT answers literally.

   This answer means, for example, that:

   • If you are shot in the leg, but don’t have lung disease, you’re in good health.
   • If you just had a heart attack, but your lungs have no disease, you are in good health

   No one believes that! So it’s virtually impossible that the argument presumed this answer was true. Answers that no one would ever believe are never correct, you have to apply a sanity filter to answers (and interpret them literally when doing so).

   You may have picked this if you prephrased that the argument improperly switched between “lung disease” and health. That is a flaw that the argument made, but this answer doesn’t describe that flaw. It’s not enough for an answer to have the right terms: it has to actually have a sensible meaning.

   A lot of LSAT answers have the pattern this one does: they sound reasonable but are actually crazy. So, if you can get the habit of interpreting answers literally and thinking of what they mean in limit cases if true, you can more easily avoid these traps.

5. It’s not a flaw to fail to consider this. There are thousands of things one can consider which are related to an argument. There’s no space to discuss every single aspect.

Recap: The question begins with “A survey published in a leading medical journal”. It is a Flawed Reasoning question. Learn more about LSAT Flaw questions in our guide to LSAT Logical Reasoning question types.