Calculates a 95 percent confidence interval for a rate difference. Uses Kirkwood and Sterne's formula for a rate difference, p241 of 2nd Ed. I think this could be re-written to work better so that it takes a data.frame as an input and compares against a given baseline.
rate_difference(numerator1, denominator1, numerator2, denominator2)The numerator for the first level for comparison (e.g. the unexposed group)
The denominator for the first level for comparison
The numerator for the second level for comparison (e.g. the exposed group)
The denominator for the second level for comparison
A dataframe with columns for rate difference, upper and lower confidence intervals
rate_difference(33, 355, 24, 518) # matches output from p241 K&S, 2nd Ed
#> rd lci uci
#> 1 0.0466257 0.009889584 0.08336182