Investigators were interested in developing preliminary data on a potential association between offering free flu shots on college campuses and diagnosed flu rates. To test their hypothesis, the investigators surveyed a random sample of 57,000 undergraduate college students between the ages of 18 and 22 years attending universities located across the US. In the survey, the study subjects were asked if free flu shots were available at their college health centers and if they had been infected with the flu while attending college. Data was also collected on potential confounders, such as age, campus flu outbreaks, and likeliness to go get the flu shot regardless of health center availability. Please assume the flu is not a rare disease.