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 particular type of cancer by comparing the number of cancers in a group of people who have a particular trait with the number of cancers in a group of people who don't have that trait.

For instance, compare the relative lung cancer risk for people who smoke with the relative 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 men who smoke is 23 times higher than the risk for men who don't smoke. So the relative risk of lung cancer for men who smoke is 23.

Relative risk is also given as a percentage. For example, the risk of lung cancer for men who smoke is 2,300 percent higher than it is for men 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 percent is the highest possible risk, but that isn't true in this case.

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

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

Source: http://www.mayoclinic.org/diseases-conditions/cancer/in-depth/cancer/art-20044092/