Problem: On a Friday, the staff in the intensive care unit was treated to lunch from a local restaurant. The following Monday morning, several of the staff reported suffering flu like symptoms over the weekend. One of the astute nurses realized that the flu like symptoms could have been food poisoning, so the nurse asked her friends what they ate for lunch last Friday. Almost all of the nurses that ate lunch on Friday were back at work on Monday morning and were able to provide information related to the food they ate and their symptoms, meeting the case definition of food poisoning. The best measure of association to use for these data would be: central tendency odds ratio risk ratio prevalence