Background
To provide comparable and applicable estimates on the benefits of different treatments, we primarily use relative treatment effects for both binary and continuous variables. For binary variables, this means using relative risks, and for continuous variables, relative mean difference (RMD) or ratio of means (ROM). These relative methods are less used for continuous outcomes; however, it may give a more accurate comparison between different treatments. This is because the absolute treatment effects for continuous outcomes are also often correlated with baseline symptoms ( «Furukawa TA, Levine SZ, Tanaka S, ym. Initial seve...»1, «Stone MB, Yaseen ZS, Miller BJ, ym. Response to ac...»2). Therefore, if treatments are tested on patients with different baseline severity of disease or risk profiles, absolute effects may not represent true differences in treatment effect. Relative effect indicates the average impact expected from treatment versus control (e.g., not starting a treatment/placebo).
However, if empirical evidence exists for the absolute treatment effect not being correlated with the baseline severity, then the mean difference may be a better option to present the treatment benefit.
Data conversion methods
Relative risk is usually reported for binary variables, so they rarely require conversion.
For continuous variables, RMD or ROM are rarely reported. Below, we describe the methods used in calculation: