Problem
A. A group of investigators are interested in conducting a clinical trial to determine whether taking bio-identical treatments prevents postmenopausal osteoporosis in women. They obtained a list of physicians in the region and recruited their patients by mailing out response cards to all eligible women; 60% of the cards were returned and 75% of those respondents entered the study. They were equally divided into the treatment group and placebo group, and were followed for 5 years to determine if they develop osteoporosis. Identify the population, sample, sampling frame, and type of study.
B. An outbreak of food poisoning occurred at a high school a few hours after 100 students ate lunch at the school's cafeteria. Most of them developed symptoms including nausea, vomiting, and diarrhea. An investigation was conducted to identify the contaminated food source. Interviews were conducted with students who ate at the cafeteria, and a food history was collected. Describe this study design (case-control, cohort, cross-sectional). Explain.