Absolute vs Relative Risk Reduction

ProfJameson Statistics 4 Comments

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


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… 0.05/0.08 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? Absolute reduction or Relative reduction. Well, they each give you different kinds of information. I prefer the absolute risk reduction, but both are important. See also the Number Needed To Treat

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