How to interpret absolute and relative risk

One of the most important set of terms to consider when reading headlines is absolute and relative risks. Relative risks are often reported in newspaper headlines. So let’s go back to our holiday goers who after a long day at the beach decided to go for an evening meal, but feel confused what to eat. If they have a steak, does it mean that the risk of developing bowel cancer increases by 20%, as the most recent headlines suggested? This is worrying, but without the context of absolute risk, or in other words baseline risk, this information is quite meaningless. Let’s look into it. For an average person, the chance of getting bowel cancer at some point in their life is around 5%.

This is an absolute risk. Relative risk is the likelihood of getting a bowel cancer in one group of people compared to another group with different behaviours or physical conditions. For example, in meat eaters compared to vegetarians. The 20% increase reported in the headline is a relative risk. Indeed it may seem like a lot, but because it hasn’t been compared to the absolute risk, it doesn’t give us a full story. At 20% relative increase equals or translates to an increase of 1% in absolute risk. Which now doesn’t sound so bad. Absolute risk numbers are needed to understand the implication of relative risks and how specific factors or behaviours affect our likelihood of developing a disease or health condition.

So next time you look at headlines, pay attention and check where the conclusions are drawn from.