“25% lower risk” of what? Reading a health headline

“25% lower risk” does not tell you how many fewer people had an outcome unless you know the starting risk. A fall from 4 in 1,000 to 3 in 1,000 is a 25% relative reduction, but the absolute difference is 1 in 1,000. These are invented numbers for learning, not findings about any treatment.

The NCI defines absolute risk as the likelihood of an event and relative risk as a comparison between groups. Keep the event and time period attached to either number.

Work through the same headline twice

Imagine two entirely fictional comparisons. Within each, both groups have the same follow-up period and the same outcome definition.

• Example A: 4 in 1,000 compared with 3 in 1,000. Difference: 1 fewer in 1,000. Relative reduction: (4 − 3) ÷ 4 = 25%.
• Example B: 20 in 1,000 compared with 15 in 1,000. Difference: 5 fewer in 1,000. Relative reduction: (20 − 15) ÷ 20 = 25%.

Both can generate the same percentage headline. They do not describe the same absolute difference. This arithmetic alone says nothing about whether either comparison is reliable or applies to you.

Percent is not the same as percentage points

In example A, 4 in 1,000 is 0.4% and 3 in 1,000 is 0.3%. Subtracting gives 0.1 percentage points. Dividing that difference by the starting 0.4% gives 25%. Calling it a “25 percentage-point reduction” would change the meaning completely.

If a headline omits the starting risk, leave the absolute difference unknown. Do not borrow a starting value from an unrelated age group, disease or follow-up period to fill the gap.

Use a six-field reading card

Copy our bilingual health-headline card, then fill these fields beside the claim:

• Outcome: exactly what event was counted?
• People: which group was studied?
• Period: over how much time?
• Comparison: what was it compared with?
• Absolute numbers: how many in the same denominator in each group?
• Uncertainty: what information or limits are missing?

This is an original reading aid, not a validated decision calculator. Blank fields are useful: they show which questions the headline has not answered.

Keep interpretation separate from a treatment decision

NCCIH's health-news checklist asks readers to consider who was studied, how long, and what limitations remain. One study rarely settles the question. A numerical comparison also does not establish that a treatment caused the difference.

For traditional medicine coverage, a separate issue is whether a term is a cultural explanation or a tested health claim; see what qi means in TCM. Keep that distinction alongside the numbers. Discuss treatment or complementary-approach decisions with your healthcare professional rather than changing care because a percentage looks large.