Im having a problem with calculating a confidence interval for an incidence rate ratio between two populations. Using PROC STDRATE from SAS, I've obtained the Incidence Rate Ratio (the difference in incidence rate between two time periods), the log rate ratio, the standard error and the z-value.
I wonder (1) why on earth did SAS not provide confidence intervals for the rate ratio? (2) How can I myself calculate these?
But this is not a mean, which is why the simple formula: SE = SD/√(sample size), probably isnt correct.
Many thanks in advance for help!