The relative risk (RR), its standard error and 95% confidence interval are calculated according to Altman, 1991.
The relative risk or risk ratio is given by
with the standard error of the log relative risk being
and 95% confidence interval
Where zeros cause problems with computation of the relative risk or its standard error, 0.5 is added to all cells (a, b, c, d) (Pagano & Gauvreau, 2000; Deeks & Higgins, 2010).