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Calculation of relative risk and 95% confidence interval
| Event | Patients | Normal | Sum |
|---|---|---|---|
| Exposed | a | b | a + b |
| Nonexposed | c | d | c + d |
Relative risk (RR) = number of patients in the exposed group/number of patients in the unexposed group = (a/a + b)/(c/c + d) = (a x (c + d))/(c x (a + b)); 95% confidence interval of 
~
where SE ln RR = standard error of ln 
