RLO: Relative Risk Reduction (RRR) and Absolute Risk Reduction (ARR)

Relative Risk and Absolute Risk - Trial Two

The second trial is conducted in a group of 100 patients who each have only one risk factor for a heart attack, and so are classed as having a low baseline risk.

Without treatment, only 3 patients out of this low risk group of 100 will experience a heart attack over the next 10 years The control event rate is 3%.

With Curit, the number of low risk patients who will experience a heart attack over the next 10 years falls to 2 patients out of 100. The experimental event rate is 2%.

Again we can express the magnitude of effect of Curit in trial 2 in two different ways:

  1. Relative risk reduction for trial 2
    RRR = (CER - EER) out of CER
    “Curit reduces the event rate of a heart attack over the next 10 years by one-third or by 33%”
  2. Absolute risk reduction for trial 2
    ARR = CER - EER
    “Curit will save 1% of patients from a heart attack over the next 10 years that would have otherwise occurred”

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