Risk is the chance that something harmful or unwanted may happen as a result of something. This could be a procedure, test or treatment. Or it may be the result of not doing anything.
Life experiences may affect our view of risk, the decisions we make and the action we take. Our views of risk are likely to change at different times in our lives depending on our circumstances.
For example, if you know someone who has had lots of side effects from having chemotherapy, your view about the risks of chemotherapy is likely to be different from someone who doesn’t know anyone who’s had it. These experiences can influence your behaviour and may make you less likely to have chemotherapy.
In this example, it’s important to remember that there are lots of different chemotherapy drugs and that not all of them cause lots of side effects. There are also some very good drugs to help prevent or reduce side effects.
Risk can be described in different ways. Healthcare professionals often describe situations as low risk or high risk. These words can mean different things to different people. Using numbers can sometimes be clearer.
Numbers can be shown in different ways. A doctor may describe risk using percentages (%), fractions or likelihood.
For example, 25 out of 100 can be described as:
Types of risk
When describing risk, research papers and doctors sometimes talk about absolute risk and relative risk.
Absolute risk is the likelihood of something happening to a person. For example, the risk of developing a certain illness in your lifetime may be 1 in 10. This can also be described as a 10% risk.
Relative risk compares risk in two different groups of people. An example would be the risk of developing lung cancer in smokers and non-smokers.
The following example may help explain absolute risk and relative risk. This is just an example and does not refer to any real medicine or research.
The doctor tells you that:
- You have a 6 in 100 (or 6%) risk of developing disease A at some point in your life.
- Research shows that if you take drug X, your risk changes from 6 in 100 to 3 in 100 (or 3%).
The reduction in risk can be described in two ways:
The absolute risk of developing the disease without drug X is 6%, but with drug X it is 3%. So the absolute risk reduction is 3%.
In this example, the risk has been reduced by half (from 6 to 3). A half can also be described as 50%, so the risk has been reduced by 50%. This is the relative risk reduction.
Relative risk reduction often sounds more dramatic than the absolute risk reduction and is used more often to describe how effective a treatment is.
We can see from this example how the way that risk is shown may influence decision making. Risk and how it relates to you can sometimes be difficult to understand. Ask your healthcare team to explain things in more detail if you’re not sure.