Suppose a case-control study was conducted in the United States to nd out whether a Black woman's exposure to racism during pregnancy inuenced her risk of giving birth prematurely. Investigators selected 500 cases who were hospitalized for premature delivery and 1,000 controls. The study found that 90 cases of mothers and 50 control mothers reported overt incidents of racism during their pregnancy. 1. Calculate and interpret the OR 2. Supposed that the investigator hires you as an epidemiological consultant to help them design this study. They ask you what type of control group is most appropriate for the study. Briey describe the control group that you would advise them to select and justify your choice. 3. The investigators also ask you to describe the purpose of the control group in a case-control study. Answer this question," why do we need a control group?"