Express treatment effects as absolute risk reduction

State treatment benefit as absolute risk reduction rather than as a relative percentage reduction when readers must understand the size of the effect. For example, say how many out of a fixed population are affected without treatment and with treatment instead of giving only a statement such as “reduces risk by 13%.”

Absolute risk reduction exposes both the starting risk and the treated risk directly. That removes a conversion step readers would otherwise have to do from a relative percentage reduction.

Mechanism: Readers can compare two stated risks directly instead of reconstructing the effect from a relative claim.

Evidence: In the experiment, numerical descriptions using absolute rather than relative risk reduction produced much higher accuracy in older adults and students; icon arrays added further gains, but the advantage of absolute wording remained large (Galesic et al., 2009).

• User Goal: Explain the size of a treatment or screening benefit in numbers.
• Task: Compare baseline risk with treated risk.
• Data: Two risks for the same outcome, without treatment and with treatment.
• Chart Setting: The message is carried in numerical text or labels accompanying a display.
• Audience: Readers with mixed numeracy.
• Success Criterion: Readers can correctly state the size of the risk reduction.

Break it when: The message is not a reduction from a baseline risk to a treated risk. Why: The source only tests absolute versus relative wording for benefit comparisons built from two risk values.

Sacrifice: A brief relative-percentage claim can sound more dramatic than the equivalent absolute statement. Risk: Using relative reduction alone can make a modest benefit seem larger than readers can accurately recover from the display. Mitigation: If you want stronger comprehension without reverting to relative-only wording, pair the absolute statement with icon arrays.

Mistake: Labeling benefit only as a relative reduction while omitting the baseline and treated risks. Why it fails: Readers are less accurate at recovering the actual size of the effect.

Failure Sign: Readers cannot tell how many people are affected before and after treatment from the wording alone. Quick Check: Compare a relative-risk-reduction phrasing against an absolute-risk-reduction phrasing for the same scenario and ask for the untreated and treated counts out of a fixed population. Stronger Test: Score whether readers derive the reduction correctly within a small tolerance rather than only recognizing that the treatment helps.

• Replace a lone relative-percentage reduction with both the untreated risk and the treated risk.
• Express those two risks over the same denominator as counts or percentages.
• Keep the comparison explicit in one sentence or one compact summary.
• If you need additional support, add paired icon arrays rather than reverting to relative-only wording.