Do not present relative risk reduction as the only treatment-effect summary
For explaining a single intervention effect, avoid relative-only effect wording on quantitative labels and captions to improve trust and mitigate inflated perceived benefit for health professionals and consumers.
- purpose:refine
- basis:empirical
- scope:single-result
- data:quantitative
- quality:trust:use
- lever:text-annotation
- communication:context
- component:caption:use
advice
Pair relative effects with baseline or absolute change
Do not leave treatment benefit as a standalone relative reduction. For example, replace “risk reduced by 50%” with “risk reduced from 10% to 5%” or “absolute reduction of 5% from a baseline of 10%,” and keep the baseline risk or absolute change next to the relative figure if you retain it.
reason
Why relative-only summaries distort treatment effects
A relative reduction hides the starting risk. That makes the same proportional change look large even when the absolute change is very small.
Mechanism: Adding the baseline risk or absolute change restores the reference level needed to judge whether the effect is small or large in absolute terms and to compare benefits with harms fairly.
Evidence: In the review, relative risk reduction was perceived as larger and was more persuasive than ARR or NNT, and the review also reported that adding baseline information to relative formats improved accuracy and reduced more positive evaluations of the message. (Akl et al., 2011)
context
Use when the display should communicate treatment benefit neutrally
- User Goal: Communicate intervention benefits without overstating them.
- Task: Help readers interpret benefit size or compare benefits with harms.
- Data: One treatment effect summarized as a risk reduction, especially when baseline risk may be low.
- Chart Setting: The effect appears in a label, caption, table cell, or text callout.
- Audience: Health professionals or consumers making or informing decisions.
- Success Criterion: Readers do not overrate effectiveness because of the wording alone.
exceptions
Do not use when the message is intentionally trying to maximize persuasion
Break it when: The communication goal is to make the intervention seem as effective as possible rather than to present it neutrally. Why: Relative risk reduction is the format that most increases perceived effect size and persuasiveness.
costs
Costs of adding baseline or absolute context
Sacrifice: You lose the shortest and most dramatic one-number summary. Risk: The label or caption becomes longer. Mitigation: Use a compact combined statement such as “from 10% to 5%” or “5% absolute reduction from a baseline of 10%.”
mistakes
Common failure with relative-effect wording
Mistake: Show only a percent reduction or other proportional change without the baseline risk or absolute change. Why it fails: Readers cannot tell whether the actual change in risk is small or large.
check
How to review this choice
Failure Sign: The display says only “reduced by X%” and never states the untreated risk or absolute difference. Quick Check: Scan the effect label and caption for a relative percentage that is not paired with a baseline risk or absolute change. Stronger Test: Compare the relative-only version with a paired version and check whether readers rate the intervention as more effective or are more willing to adopt it under the relative-only version.
fix
What to change
- Add the untreated baseline risk next to the relative reduction.
- Replace the relative-only statement with treated-versus-untreated risks.
- Replace the relative-only statement with an absolute reduction when space is limited.
- Use one compact sentence that includes both baseline and change if a relative figure must stay.