Passage Summary: A researcher notices that long-sleepers are sick more often than short-sleepers, so they conclude that sleeping less actually makes you healthier.

Conclusion: Mild sleep deprivation is likely healthy and helps the body defend itself against illness.

Reasoning: A large survey found that people who regularly sleep at least 8 hours a night get sick more often than those who sleep less.

Analysis: This argument falls into the most common trap in logic: confusing correlation with causation. The researcher assumes sleep length causes the health status, but it is just as likely (if not more so) that the health status causes the sleep length. People who are already ill often need more sleep to recover. Look for an answer that points out this 'reverse causation'—the possibility that being sick is what's making people sleep 8+ hours in the first place.