Clear Health Communication: Do the Math for Your Audience

When health materials include numbers, CDC's Clear Communication Index — a tool for making public health messages easier to understand — asks a simple question: does the audience have to do any math? If so, the communicator should do it for them.

Why

Asking readers to calculate distracts, confuses or intimidates them, and invites errors that leave them misinformed. Few people will take the time to do even basic addition and subtraction, and some cannot. Research shows that even health professionals and trained statisticians can make wrong assumptions and calculation mistakes, depending on the context and the kind of calculation.

Two rules

• Provide the calculations and conversions rather than leaving them to the reader.
• Keep denominators constant. When numbers are expressed with different denominators, people cannot easily compare them. Use the same one throughout — even for absolute risks such as "1 out of 3" — so readers do not have to convert.

Examples

A calculator. CDC's body mass index (BMI) calculator works out a person's BMI and the matching weight category, so users do not have to compute it themselves.

A tool that does the calculation for the user. CDC

A worked example. Rather than asking readers to estimate what they spend on alcohol, one counseling program did the arithmetic for them: someone who had three drinks a day at $4 each spent $4,380 last year on alcohol — and could ask what else that money might buy this year.

Sources

• Centers for Disease Control and Prevention, Clear Communication Index, "Does the audience have to conduct mathematical calculations?": https://www.cdc.gov/ccindex/tool/page-17.html
• The alcohol example is adapted there from CDC's CHOICES: A Program for Women About Choosing Healthy Behaviors.