In a recent JAMA Insight, Ellen Peters, PhD, and Nadine S. Jennings, MD, describe a simple but powerful communication problem in medicine: numbers presented without comparisons are often meaningless to patients.
Consider a common clinical example.
Telling a patient with diabetes that their stroke risk is 11% sounds informative. But without context, that number floats in space. Patients often leave the conversation wondering: Is that high? Low? Something to worry about?
Now add one number:
“Given that you have diabetes, your risk of stroke is 11%, compared with 4% in the general adult population.”
Suddenly, the statistic becomes interpretable.
Research shows that comparisons fundamentally change how people interpret risk. In one study cited by Peters and Jennings, women were told their breast cancer risk was 6%. Some participants were told the average risk was 3%, while others were told it was 12%. Women who heard their risk was higher than average were significantly more likely to say they would take a risk-reducing medication than women who were told their risk was lower than average.
The risk never changed — only the comparison did.
The practical implication is straightforward: risk numbers are far more meaningful when paired with a second number. That comparison might show risk with versus without treatment, treatment A versus treatment B, or an individual’s risk versus the population average.
Another study demonstrates how comparisons shape perceptions of treatment effectiveness. Participants evaluating a fictitious pain drug rated it as more effective when no placebo data were provided than when they were told the placebo worked nearly as well. Without a comparison point, participants inferred greater benefit.
In other words, silence about the alternative was not neutral — it subtly inflated perceptions of effectiveness.
Peters and Jennings cite research on evaluability to explain why. Isolated numbers are difficult for people to interpret emotionally or practically. Without a reference point, patients struggle to understand magnitude.
Two numbers, rather than one, can transform abstract statistics into information patients can interpret when making decisions.
The authors reported no conflicts of interest.
Source: JAMA