Statistics - explanations and formulas

Relative Risk

The relative risk is the proportion of bad outcomes in the experimental group divided by the proportion of bad outcomes in the control group.

For this example:

Acetazolomide event rate was .43; Budesonide event rate was .73.

Math: .43/.73 =.59

Another way to say that is only 15 of 35 (.43) participants who took Acetazolamide acquired symptoms of acute mountain sickness compared with Budesonide where 24 of 33 (.73) acquired the symptoms.

Table with statistical values entered into boxes

Lipman, G. S., Pomeranz, D., Burns, P., Phillips, C., Cheffers, M., Evans, K., Jurkiewicz, C., Juul, N., & Hackett, P. (2018). Budesonide Versus Acetazolamide for Prevention of Acute Mountain Sickness. The American journal of medicine, 131(2), 200.e9–200.e16.


Relative risk less than one means the risk was higher in the control group.

Relative risk greater than one means the risk was higher in the experimental group.

Relative risk equal to one means there was no different in the risk between the two groups.


Relative Risk Reduction

Relative Risk Reduction tells you by how much the treatment reduced the risk of bad outcomes relative to the control group who did not have the treatment.

In the above example, Acetazolamide decreases the risk of developing acute mountain sickness by 41% as opposed to Budesonide.