  The Risk Ratio (RR) is the ratio of the outcome among the exposed to risk of
the outcome among the unexposed. This is a simple concept, which makes one
wonder why it has not gained the same popularity as the odds ratio. Using
logistic regression to estimate the odds ratio is quite common in epidemiology
and interpreting the odds ratio as a risk ratio, under the assumption that the
outcome is rare, is also common. On one hand, estimating the odds ratio is
simple but interpreting it is hard. On the other, estimating the risk ratio is
challenging but its interpretation is straightforward. Issues with estimating
risk ratio still remains after four decades. These issues include convergence
of the algorithm, the choice of regression specification (e.g. log-binomial,
Poisson) and many more. Various new computational methods are available that
help overcome the issue of convergence and provide doubly robust estimates of
RR.
