A TedEd by Gerd Gigerenzer
Risk can be represented in two ways: absolute and relative. Relative risk is comparing risk to the previous risk, while absolute percentages are represented in the current overall percentage. Let's say there is a new drug that can reduce heart attacks. Out of 1000 people in a control group, 10 get a heart attack. In a group that gets the drug, only 6 do. That means there is a relative risk reduction of 40%, while the absolute risk goes from 1% to 0.6% - not a big change. The relative risk reduction makes the drug seem more substantial. But let's say it caused cancer in 0.5% of the patients. In our group of 1000, there would be 4 less heart attacks, but 5 more cases of cancer. Even though the relative percentage of 40% sounds much bigger than the absolute cancer risk of 0.5%, they end up in about the same number. However, risk evaluation varies for everyone. If you know that you have a genetically high risk of heart attack, you might take the drug despite the chance of getting cancer. There are also many cases with no correct answer. Some may skip a swim in the ocean because of the tiny probability of a shark attack, while others wouldn't dream of such a thing. But understanding how measures of risk work is a good step toward making sure you do it right.
