Reading risk claims without losing the starting point

A headline may say that something doubles a risk or cuts it in half. The size sounds dramatic, but the phrase leaves an important question unanswered: what was the risk before the change?

Risk is the chance of a specified outcome under specified conditions over a period of time. To understand a change in risk, keep the outcome, starting level, population, and period together.

This lesson uses fictional numbers to explain the comparison. The same reading method helps with news about safety, health, technology, and other uncertain outcomes.