Risk

In research, risk can be categorised as absolute or relative.

• Absolute risk is a measure of the risk of a certain event happening.
• In cancer research, absolute risk is the likelihood that a person who is free of a specific type of cancer at a given age will develop that cancer over a certain period of time.
• For example, a woman 35 years of age, with no known risk factors for breast cancer, has an absolute risk of getting breast cancer over a lifetime of 90 years of about 13%, meaning she has a 1 in 8 chance of developing breast cancer. This also means the chance that she will never have breast cancer is about 87%, or 7 in 8.
• Relative risk is a measure of the risk of a certain event happening in one group compared to the risk of the same event happening in another group.
• In cancer research, relative risk is used in prospective (forward looking) studies, such as cohort studies and clinical trials.
• A relative risk of one means there is no difference between two groups in terms of their risk of cancer, based on whether or not they were exposed to a certain substance or factor, or how they responded to two treatments being compared. A relative risk of greater than one or of less than one usually means that being exposed to a certain substance or factor either increases (relative risk greater than one) or decreases (relative risk less than one) the risk of cancer, or that the treatments being compared do not have the same effects. Also called risk ratio.