Rate Difference (RD) 1
Rate Difference (RD) 1 : The absolute difference between two rates, for example, the difference in incidence rate between a population group exposed to a causal factor and a population group not exposed to the factor: RD = Ie - Iu. where Ie= incidence rate among exposed, and Iu = incidence rate among unexposed. In comparisons of exposed and unexposed groups, the term excess rate may be used as a synonym for rate difference