A study conducted in a city to examine whether cyclists were more prone to injury than pedestrians. 1500 participants across the city were surveyed beginning January 1, 2003. On June 5, 2003, it was discovered that 75 of those participants currently had injuries. After June 5, the remaining injury-free participants were enrolled in a cohort study, classified as cyclists (n=1000) and pedestrians (n=425), and followed for 3 years. 85 cyclists and 15 pedestrians became injured in the 3 years. All follow-up stopped on exactly June 5, 2006. Assuming complete ascertainment and no drop-outs:
1) Calculate the point-prevalence of injury on June 5, 2003.
2) Calculate the cumulative incidence of injury in the entire sample between June 5, 2003 and June 5, 2006.
3) Calculate the relative risk of injury among cyclists compared to pedestrians, and interpret the results.
Sample Solution