A company is concerned with the high cholesterol levels of many of its employees. To help combat the problem, it opens an exercise facility and encourages its employees to use this facility. After a year, it chooses a random 100 employees who claim they use the facility regularly, and another 200 who claim they don’t use it at all. The cholesterol levels of these 300 employees are checked, with the results shown in the file P09_72.xlsx.
a. Is this sample evidence “proof” that the exercise facility, when used, tends to lower the mean cholesterol level? Phrase this as a hypothesis testing problem and do the appropriate analysis.
Do you feel comfortable that your analysis answers the question definitively (one way or the other)? Why or why not?
b. Repeat part a, but replace “mean cholesterol level” with “percentage with level over 215.”
c. What can you say about causality? Could you ever conclude from such a study that the exercise causes low cholesterol? Why or why not?