ThinkCritical.eu · Manipulation atlas
Numbers and chartsRelative without absolute
“A third lower” sounds dramatic even when the difference is one case in a thousand.
A relative number tells you how much a risk changed compared with where it started. An absolute number tells you how many people it actually affects. When the starting risk is small, even “half the risk” can mean a difference of a few people in a thousand.
An advert for a new door lock: “Our lock cuts the risk of burglary by 50%!” According to the maker's own figures, 4 in 1,000 flats with the old lock were burgled each year and 2 in 1,000 with the new one. The risk halved – but the difference is 2 flats in a thousand, or 0.2 percentage points.
How to spot it
- The change is given only as a percentage or fraction (“a third lower”, “double the risk”) without the number of cases.
- It concerns something rare – an illness, an accident, a burglary – yet the change sounds dramatic.
- The text doesn't say how many people out of 100 or 1,000 are affected with and without the measure.
How to check and what to do
- Look for absolute numbers: how many people out of 1,000 were affected in each group.
- Work out the difference in percentage points – simply subtract one share from the other.
- Ask how many people need the measure for one of them to benefit – and what it costs or what side effects it has.
- For health news, read the original study or ask a doctor or pharmacist.
Tip: “Double the risk” of something that happens to one person in a million is still only two people in a million.
Full explanation and exercises:
thinkcritical.eu/en/manipulation-atlas/relative-risk