You conducted a study on the efficacy of seatbelt use against the incidence of a skeletal fracture among persons involved in an automobile crash. the cases in each study were persons who sustained a fracture in a car crash. controls were persons in crashes who did not sustain a fracture (assume all other characteristics and exposures were identical). 1,000 cases and 1,000 controls were enrolled in this study; of the cases, 322 had worn seat belts whereas 500 of the controls had. what is the study design?