Medical researcher: A survey of more than 1 million adults found that there was a greater frequency of illness among people who regularly slept at least 8 hours a night than among people who slept significantly less.
Conclusion
Mild sleep deprivation isn't unhealthy, and it probably even helps, by helping us to avoid illness.
Evidence
(correlation: greater frequency of X among people who are Y) In a huge survey, there was a correlation between
sleeping 8+ hours || higher rate of illness
Like almost all LSAT authors, they went on to overconfidently state their presumed version of the causal story that's goin' on here.
When an author presents a Curious Fact and then concludes her presumed Explanation, we're supposed to ask two different questions: - is there some Alternate Explanation for the Curious Fact? - how plausible is the Author's Explanation?
With a correlation, the two Alternate Explanations that should come immediately to mind are
REVERSE CAUSALITY sleeping 8+ hours ← higher rate of illness
THIRD FACTOR sleeping 8+ hours higher rate of illness ↑ ↑
genetic condition? exhausted school teachers?
Goal
For an answer doing one of these things: - calling out the illegal correlation proves causation move - suggesting it could be reverse causation - suggesting the correlation could be tied to some third factor