medium · LSAT Logical Reasoning
A large-scale medical study found that individuals who consume three or more cups of coffee daily reported significantly higher quality of sleep than non-coffee drinkers. This result surprised researchers, given that caffeine is a well-known stimulant that typically interferes with sleep.
Which one of the following, if true, most helps to resolve the researchers' surprise?
- Participants who drank no coffee at all were considerably more likely to report feeling groggy and persistently unfocused throughout the early morning hours.
- Many people who drink coffee steadily throughout the day also eat sugary snacks that can trigger a sharp energy crash later in the evening.
- Caffeine has a half-life of roughly six hours in the average adult human body, so a meaningful dose still lingers in the bloodstream at night.
- The participants who drank three or more cups of coffee also tended to exercise more vigorously, an activity strongly associated with better sleep.
- The study measured each participant's nightly sleep quality through written self-reports rather than through direct, in-lab clinical observation.
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