Comparing two quantities by using a ratio

where nij are sometimes replaced by 0.5 ij n + , when some of the ij n are zero. This result can be derived under the assumption of multinomial sampling by using the Delta Method. When RR is used to compare two quantities, the log transformation is conducted, that is ( ) 1|1 1|2 ˆ ˆ log / π π is often considered instead of ( ) 1|1 1|2 ˆ ˆ / π π , since the former has a sampling distribution which is closer to normal than that of the latter. The estimated asymptotic standard error (ASE) of log(RR):