PIF TICK guide

Making sense of risks and benefits

Need to make a decision about an operation or a medicine? You should get information on the risks and benefits of different options, including what is likely to happen if you do nothing. This should include data to help you understand your choices. Here are some tips to help you make sense of this information.

What do words like ‘common’ and ‘rare’ actually mean?

Words like ‘rare’ or ‘common’ mean different things to different people. People may overestimate the risk of ‘common’ for example.

Words like ‘rare’ or ‘common’ should come with a number to explain them. Ask if you are unsure about a word or number in health information.

Here is how the European Medicines Agency defines these words:

Very commonMay affect more than 1,000 in 10,000 people.
CommonMay affect up to 1,000 in 10,000 people.
UncommonMay affect up to 100 in 10,000 people.
RareMay affect up to 10 in 10,000 people.
Very rareMay affect up to 1 in 10,000 people.


Benefits and risks should be given ‘out of’ or ‘in’ the same number. This should make it easier for you to compare.

For example:

    1 in 10 compared with 2 in 10

    1 in 10 compared with 1 in 5

These numbers are sometimes shown in an icon array like this:

Example of an icon array


Ask how certain the data is and what this means for you. Are you at higher or lower risk than average risk?

Actual risk not relative risk

If you are told a risk ‘doubles’ or ‘halves’, ask what number it changes from and what it changes to. 

For example, if the risk ‘doubles’ the actual change may be from 1 in 1000 to 2 in 1000.

You need to know the actual numbers to be able to think about how serious the risk feels to you.

Pros and cons

Risks can be put in negative and positive ways. For example, ‘3 out of 100 people had this side effect, but 97 out of 100 did not’. It can help to think about the risk both ways.

What can risk and benefit data tell me?

Data comes from real people, often from clinical trials or hospital statistics. It can tell you what happens to most people. This can help you make an informed decision about whether to have a treatment or to do nothing.

Download the PDF guide

Making sense of risks and benefits

Publish date: November 2021
Review date: November 2023

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