Category FAQs Search : Health
Question: Understanding the difference between absolute and relative risk for cancer:
Answer: Doctors use absolute risk and relative risk to assess if a person's risk is higher or lower than that of either the general population or a certain group of people.
Absolute risk is the chance that a person will develop a disease during a given time. This identifies how many people are at risk for a disease in the general population.
For instance, consider the statement “1 out of 8 women (12.5%) will get breast cancer in her lifetime.” This describes the absolute risk for the general population of women. It cannot identify the risk for a certain person or group of people. For example, absolute risk cannot show if a group of older women has a higher risk of breast cancer than a group of younger women.
Relative risk compares the risk of disease between two groups of people. It compares one group with a certain risk factor for a disease to another group’s risk.
For instance, imagine you are comparing the risk of breast cancer among 2 groups of 100 women. But only the women in 1 group have a certain risk factor for breast cancer. The other group of women does not have this risk factor. Researchers keep track of how many people from each group develop cancer over a certain time. Let’s say they find that 2 women who have the same risk factor get cancer. But only 1 woman without this risk factor gets cancer. Then those in the first group have 2 times the risk of the second group. This is a 100% increase in relative risk. The absolute risk, however, would be 2% or 2 out of 100 people.
Patients can use risk measurements to make better choices about lifestyle changes or cancer screening. It is also important to know the difference between absolute and relative risk. For instance, the relative risk in the last example might sound high. It identified a person’s relative risk of developing cancer by 100%. But look at the absolute risk to get a more complete picture. That is, 1 person in 100 compared to 2 people in 100. If you want to compare the research you hear about in the news to your own situation, make sure you find the absolute risk. Most research studies report relative risks. This can make the risk sound higher than it actually is.
(Source: Cancer.Net, 16 Mar 2021)