Communicating Relative Risk Changes with Baseline Risk: Presentation Format and Numeracy Matter.

Area of Science:

• Health communication
• Risk perception
• Medical decision-making

Background:

• Relative risk reductions and increases are often misunderstood by both healthcare providers and patients.
• Communicating baseline risk alongside relative risk changes is a proposed method to enhance understanding.
• This study investigates how baseline risk presentation format affects understanding of relative risk changes and the role of numeracy.

Purpose of the Study:

• To determine if the presentation format of baseline risk influences the understanding of relative risk changes.
• To examine the mediating role of numeracy skills in understanding treatment benefits and harms.
• To assess the effectiveness of frequency versus percentage formats for baseline risk communication.

Main Methods:

• 1234 laypeople were presented with hypothetical treatment scenarios involving heart disease risk.
• Baseline risk was communicated either as a percentage or a frequency.
• Participants judged treatment group risk based on relative risk changes and baseline risk; numeracy was assessed.

Main Results:

• A frequency format for baseline risk improved understanding of treatment benefits and harms, unlike the percentage format.
• Many participants misinterpreted relative risk reduction as absolute risk reduction when percentages were used.
• Higher numeracy correlated with better understanding, but all participants benefited from the frequency format.

Conclusions:

• Presenting baseline risk in a frequency format enhances comprehension of relative risk information, while percentages often lead to misinterpretation.
• Numeracy skills are crucial for understanding medical information, but a frequency format is universally beneficial.
• Communicating treatment benefits and harms via relative risk changes remains challenging, even with explicit baseline risk data.