Risk Communication: Information for the Clinician about Colorectal Cancer Risk

Describing Risk

Risk of colorectal cancer can be expressed in four ways: relative risk,attributable risk, absolute risk and lifetime risk. Each of these measures is useful for specific purposes, but their use in the popular media, where they are often taken out of context, can lead to confusion. Misinterpretation of statistics has caused a great deal of unnecessary fear in the general public. At the same time, misunderstandings can obscure the important message about the demonstrated benefits of early detection of colorectal cancer.

• Relative risk is a measure of the relationship between a given risk factor and a disease. It compares the incidence or mortality among individuals with a specific risk factor to those without that risk factor. The larger the relative risk associated with a given factor, the more likely it is to be an important factor for a disease. Relative risk is used mainly in describing the causes of a disease. For example, smokers have roughly a 10-fold increased risk of lung cancer compared to those who have never smoked, or a relative risk of 10:1. (14)



• Attributable risk addresses the question: How many cases of a disease could be eliminated if a specific factor were removed? It is the difference in incidence between those with a trait or exposure and those without that trait or exposure. Attributable risk is useful in gauging the importance of a risk factor from the point of view of public health. A factor can have a small relative risk and yet have a large attributable risk if it has a high prevalence in the population. This is true of the role of smoking in causing heart disease. The relative risk for heart disease among smokers compared to never smokers is much smaller than for lung cancer. However, even with a smaller relative risk, the number of cases of heart disease caused by smoking is larger than the number of lung cancer cases caused by smoking. Thus, the attributable risk due to smoking is greater for heart disease than for lung cancer.



• Absolute risk is the incidence of disease in a given population. It can indicate the magnitude of disease in a given population with a certain exposure. However it does not take into consideration the risk of disease in the unexposed population. (15)



• Lifetime risk is the probability that an individual in his or her lifetime will be diagnosed with, or die from, a certain disease.  Both men and women in the United States have a lifetime risk of about 5-6% for colorectal cancer, or 1 in 19. (44)  However, the risk only reaches this level if a person lives to be 85. (1)  Rather than thinking about lifetime risk, it is more informative and less alarming to think about the probability of developing colorectal cancer within certain age intervals, as shown below:

Cancer Facts and Figures 2008. American Cancer Society.