Hypothetical cohort | Helmet | No helmet | Total | Incidence rate ratio |
---|---|---|---|---|
Cases | 2 220 | 5 350 | 7 570 | (2220/149554)/(5350/113746) = 0.316 |
Bicycle riding hours | 149 554 | 113 746 | 263 300 | |
Incidence density sampling from the population experience: | ||||
Odds ratio | ||||
Cases | 222 | 535 | 757 | (222/1496)/(535/1138) = 0.316 |
Controls | 1 496 | 1 138 | 2 634 |