Suppose that a study of oral contraceptive (OC) use and development of bacteriuria was conducted among 2,390 women, all of whom were initially free from bacteriuria. At the start of the study, the women were surveyed to determine whether or not they currently used OCs. 482 were using OCs and 1908 were not. By the end of the follow-up period, a total of 27 of the OC users and 77 of the non-users had developed bacteriuira.

A. What type of study is described here?
B. Set up the two-by-two table for these data.
C. Calculate the risk ratio describing the strength of the relationship between OC use and bacteriuria; interpret the result in one sentence.
D. Give one numerical example of a risk ratio that would have indicated that OC are protective against bacteriuria.