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Absolute risk reduction

The ARR is the difference in the risk of an event occurring between two groups of patients in a study – for example, if 6% of patients die after receiving a new experimental drug and 10% of patients die after having the old drug treatment then the ARR is 10% – 6% = 4%. Thus by using the new drug instead of the old drug 4% of patients can be prevented from dying. Here the ARR measures the risk reduction associated with a new treatment. See also absolute risk.