Biomarkers of risk, things like blood pressure and cholesterol, are factors that predict risk. However, while high blood pressure (BP) is related to risk, the relationship is not linear. This visual is designed to help a person who receives an elevated BP level (e.g., at a doctor’s visit) recognize (a) that their risk is elevated AND (b) that further increases in BP would be really bad.
This variant of a bar graph uses circle size / area to represent elevations in risk as blood pressure increases. Because the circles are aligned at the base, the circle edges create an upwardly curving exponential shape which helps evoke a sense of increasing risk.
The overlapping circles at the higher levels convey an additional gist sense of being “large” that may help viewers recognize that further elevations in blood pressure result in particularly large levels of risk.
When compared to other, similar graphics, people who viewed this graphic were more likely to perceive and classify their blood pressure risk as slightly above normal vs. way above normal. Please note that this may be due to the particular algorithm used for circle size rather than the format itself. Our recommendation is therefore unclear. We believe the choice of graphic should depend on whether the goal is to maximize motivation to act vs. calibration of risk perception response to an elevated (but not extremely elevated) BP level.