A survey published in a leading medical journal in the early 1970s found that the more frequently people engaged in aerobic exercise, the lower their risk of lung disease tended to be.
Conclusion (it must be)
Aerobic exercise has a significant beneficial effect on people's health.
Evidence (since)
Other surveys in addition to one in a leading medical journal in the early 1970s have found that the more frequently people engaged in aerobic exercise, the lower their risk of lung disease tended to be.
Evaluate
Since the evidence is presenting a Correlation (the more X, the more there tends to be Y) and the conclusion is suddenly moving to Causation (X has a significant beneficial effect on Y), we can use our Explain Curious Fact framework.
Curious Fact ... Why do these studies find a correlation between more frequent aerobic exercise and lower risk of lung disease?
Author's Explanation ... Aerobic exercise is having a beneficial effect on people's health, thereby causing their risk of lung disease to be lessened.
We always evaluate this framework by asking 1. Could there be some Alternate Explanation for the curious fact? 2. How plausible is the Author's Explanation?
When we encounter arguments like this one where the author says, , we reflexively consider the two alternate explanations that LSAT loves to test:
- what if it's Reverse Cause? What if Y causes X? In this case, that means what if having lung disease (or the precursors of lung disease) causes people to not partake of aerobic exercise?
- what if there's some 3rd Factor? What if Z causes X and Y? In this case, that means what if there is some causal factor that both explains why someone does a lot of aerobic exercise and explains why they have lower risk of heart disease (or a factor that explains why people don't exercise and do have lower risk of heart disease).
Goal
On Flaw and Weaken, we're unlikely to see answers that make the author's hypothesis seem implausible. We're much more likely to see answers that deal with the existence of Alternative Explanations for the curious fact.
On Flaw, we can simply point out that the author has illegally convinced herself that a correlation indicates a causal relationshp.
Or we can raise the possibility of an alternate explanation (such as reverse cause or 3rd factor).