Imagine that you are conducting an experiment to prove that the correlation in the previous question is a causal relationship. You recruit 10 friends, and randomly assign them
to two groups: One group will keep their normal schedule and the other group will be
excused from their morning class so that they can sleep an extra hour in the morning. Using
the same Web application, you ask the subjects to report the number of hours they slept,
along with how sleepy they feel three times during the day.

You find a weak negative correlation between the hours of sleep and self-reported
sleepiness.

1.) Explain what a negative correlation is, and if you found this in your experiment, what
would it mean?

2.) Explain what a hidden variable is. What is a hidden variable that might be at work in this study? How could it have affected the results?

3.) If the hypothesis for this study was “increased sleep will decrease absences”, does this experiment clearly prove or disapprove the hypothesis? Explain why.