Health, Explained · 55 sec
Relative Risk Can Make a Small Effect Look Huge
‘Risk reduced by 50%’ may mean a change from two people in 10,000 to one.
The useful idea
- Relative change
A fall from two cases in 10,000 to one case in 10,000 is a 50% relative reduction.
- Absolute change
The same result is an absolute reduction of one case in 10,000, which describes the scale differently.
- Read both
The baseline risk and absolute difference are needed alongside the relative figure to judge practical importance.
Why this matters
Large percentages can exaggerate how large a benefit or harm feels when the starting risk is tiny.
Try this
When you see a risk percentage, ask: ‘From what baseline, and what is the absolute change?’
Test your recall
A risk falling from 2 in 10,000 to 1 in 10,000 is what absolute reduction?
- 1 in 10,000 — correct
- 50 in 10,000
- 5,000 in 10,000
The relative reduction is 50%, while the absolute reduction is one case per 10,000.
General education only — not medical advice, diagnosis, or treatment.