Ferris State University | College of Pharmacy | Professor of Pharmacy Practice

One Minute Genius

Absolute vs Relative Risk Reduction

John and Albert skydiving Albert and I developed an acute interest in risk reduction at about 3500 feet.

Scroll down for what we discovered


Absolute vs Relative Risk Example

Example 1A:
Consider the benefit of using Coumadin for Stroke prevention in Atrial Fibrillation
  • Moderate risk patients on placebo have 8% risk of stroke in ONE year
  • Coumadin decreases that to 3% risk of stroke in ONE year
  • Quick !! Instinctively, what is the risk reduction? ..... 5% , right?
    That's absolute risk reduction, NOT relative to anything else.

    Relative Risk reduction is RELATIVE to the baseline 8% so... .05/.08 or 5% reduction /8% baseline = .62 or 62% relative risk reduction

    Example 1B:
    OK, now consider if there was a very high baseline risk of 93%
  • Suppose Coumadin decreased the risk to 88%
  • Quick !! The absolute reduction is? .... You're right! 5% (the same as the first example)
  • The relative risk though is different. 5 / 93 = 5.3% relative risk reduction So which is the most important? Well, they give you different kinds of information. I prefer the absolute risk reduction, but both are important. See also the Number Needed to Treat