Passage Summary: People who smelled peppermint slept worse than those who smelled orange; since orange doesn't do anything, the peppermint must be keeping people awake.

Conclusion: Inhaling peppermint scent has a negative impact on a person's ability to fall asleep.

Reasoning: In a study, peppermint users struggled more than bitter orange users, and since bitter orange is known to be neutral, peppermint must be the culprit.

Analysis: The argument assumes the peppermint is the active cause of the sleep trouble, but it ignores the possibility that the groups were different before the scent was introduced. If the peppermint group already had more severe insomnia than the orange group, the scent might be blameless. Look for an answer that suggests the peppermint group was predisposed to have more trouble sleeping regardless of the scent. Correlation in a study does not always equal causation, especially if the study groups weren't balanced.