Risks and Probability


Numbers can be used in different ways to mean the same thing. Here is a guide to help:

If 100 people have an anaesthetic and 10 feel sick afterwards, the risk may be described as 10 in 100 OR 1 in 10.  This is also the same as 10% (or 10 per cent).

More examples:

1 person in 100 1 in 100 1%
1 person in 1,000 1 in 1,000  0.1%
1 person in 10,000 1 in 10,000 0.01%
50 people out of 10,000 50 in 10,000 OR 1 in 200 0.5%


In this website, we have linked numbers to words like this:

For example in the sentence 'nerve damage is rare' – you know that it means that the risk of nerve damage in that circumstance is about 1 in 10,000. You will also find that more exact numbers are used in some places, to give you the best information available.


Pictures and diagrams are sometimes used to help you understand what is meant by these numbers. This may help you decide how you feel about the risk that has been explained to you.

The way you feel about a risk is very personal to you, and depends on your personality, your own experiences and often your family and cultural background. You may be a 'risk taker', a 'risk avoider' , or somewhere in between. You may know someone who has had a risk happen to them, even though that is very unusual. Or you may have read in the newspapers about a risk and be especially worried about it.

The following diagram may help you decide how you feel about a risk:


More detailed thoughts about risk

If you would like to read in more detail about communicating risk, you may like to go to 'Risk communication and anaesthesia', the second chapter of Section 3: Principles in Raising the Standard: Information for patients. This article was written primarily to help anaesthetists think about how to give information to people about risks. 

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