Relative risk

Relative risk gives you a comparison or ratio rather than an absolute value. It shows the strength of the relationship between a risk factor and a certain type of cancer. It does this by comparing the number of cancers in a group of people who have a certain trait with the number of cancers in a group of people who don't have that trait.

For instance, compare the lung cancer risk for people who smoke with the lung cancer risk in a similar group of people who don't smoke. You might hear relative risk being expressed like this: The risk of lung cancer for people who smoke is 25 times higher than the risk for people who don't smoke. So the relative risk of lung cancer for people who smoke is 25.

Relative risk also can be given as a percentage. For example, the risk of lung cancer for people who smoke is 2,500% higher than it is for people who don't smoke.

When you hear about relative risk, there's no upper limit to the percentage increase in risk. Most people think 100% is the highest possible risk, but that isn't true with relative risk.

A relative risk of 100% means your risk is twice as high as that of someone without that risk factor. A 200% relative risk means that you are three times as likely to develop that condition.

Risk seems greater when put in these terms. A 100% increase in risk may seem huge. However, if the risk began as 1 in 100 people, a 100% increase in risk means that 2 out of 100 will be affected.