Risk prediction, risk management, and risk avoidance are in fashion and invading medical practice, but current terminology is unfortunate and tendentious in a clinical context. Gambling and life insurance led to the first mathematics of risk. Individual outcomes were unpredictable, but if the circumstances and rules of the game did not change, the long run odds could be estimated from previous experience.

Longitudinal studies, of which the Framingham study was a pioneer, identified human risk factors which, when measured at the start of observation, correlated with the subsequently recorded risk. Risk is recorded as an event rate having numerator, denominator, and time period, but problems arose in how to portray different levels of risk at different levels of risk factors.

“Absolute” risk…has misleading medicolegal and ethical implications

For half a century relative risk was king. Dividing high risk by low produced a simple multiple with no units—relative risk of smoking = 2.5. Relative …