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Risk - What do we mean?

Dr Roger Henderson
Reviewed by Roger HendersonReviewed on 29.04.2024 | 5 minutes read

As doctors, we talk about risk all the time – it's part of our job to weigh up the risks and benefits of giving a medication, not giving it, doing surgery that may help or may cause damage. And we talk about these odds as if the best next step is obvious.

But it’s hard to weigh up risks before making a decision, and they can mean different things to different people. Let’s turn to the races. Backing a horse with the lowest (or shortest) odds to win the Grand National – let's say odds of 100 to 1 – means high risk but potentially high gains. The numbers are fact. But the odds mean something different to everyone: for some, it may be an unacceptable chance of losing your money, but others can only see potential gains, as they’ll win big if the horse does win.

Likewise, any chance of erectile dysfunction may be unacceptable to many men, no matter how low. Others may consider prostate surgery for cancer is worth it. Others may be in the middle – it's acccetable under certain circumstances, such as taking anti-depressants, as they can feel better, but the side effect can be reversed if they develop erectile dysfunction and want to stop taking the tablets.

It’s true to say that every treatment, surgery or chance of something happening carries a level of risk – we need to communicate how often the risk happens, how serious it might be, and alternative options.

Let’s talk you through what the medical community means by risk, and how we refer to it here. And in any consultation, if you don’t understand something or need it explained differently, don’t be afraid to ask.

How common is common?

We sometimes refer to things as common or rare. There is a distinct classification for these terms, based on risk, and usually used in how often side effects of a medication occur. Common means a chance of more than 1 in 100 of anyone getting a certain side effect from medicine. You might imagine all the seats filled on a London double decker bus, and one person gets the side effect.

This risk can become very common if it’s more than 1 in 10 – think of one person in a busy corner shop.

Rare means a risk of more than 1 in 10,000. You might imagine your target 10,000 steps per day, and just one of these is the risk. Very rare is even less likely to happen than this. Uncommon is if it’s more than 1 in 1000.

A similar scale can be used if you are presented with high risk (equating to “common” or more than 1 in 100 or 1%) versus low risk (“rare” or more than 1 in 10,000 or 0.01%). There are varying degrees within this scale – moderate (between high and low) and minimal and negligible, both less than low risk.

What about risk over time?

An event may be so rare that we need to add in time to our risk estimates. We all know lightning doesn’t strike twice, but the chance of hitting you just once over the average lifetime is 1 in 10,000.

Heart attacks are another good example. As doctors, we put in lots of factors that we know can affect people and raise their risk of a heart attack (your age, weight, whether you smoke, where you live, certain blood results) and tailor-make the risk to you.

This QRISK3 gives a chance in percentage of you getting a heart attack or stroke within the next 10 years. This percentage is useful to urge you to modify any lifestyle factors to improve it, such as losing weight and stopping smoking. If you have a 10% risk or more, this is considered high, and your doctor will offer medication to further reduce your risk.

You will be offered a statin to keep your blood vessels healthier and hopefully protect you from a heart attack or stroke.

How do I weigh up one risk over another?

A good example here is discussing the combined contraceptive pill with women. There’s a risk of blood clots, called VTE (venous thrombo-embolism), either in your legs (deep vein thrombosis) or lungs (pulmonary embolus). These can be serious - a pulmonary embolus can be life-threatening.

They discuss the risk with you. The risk increases if you are a certain age, if you smoke and if you are obese, among other factors. Certain brands increase the risk, ie those with higher oestrogen content, but that might be to treat PCOS alongside. Some of these risks are in discussion with you, some are too high for your doctor to safely prescribe no matter your preference, and some may be acceptable to both of you, for example to treat PCOS symptoms.

The risk of a clot is extremely low. But the medical community doesn’t want otherwise healthy young women to be put at undue risk.

And this is on a background risk that you may then not take contraception at all, and become pregnant. Pregnancy has a much higher chance of blood clots in itself. And an unexpected or unwanted pregnancy brings a host of other issues, too.

This risk business is complicated, isn’t it?

I’m still confused, what now?

Risks can be further complicated with divisions into serious events occurring, which may be less frequent but carry a risk of perhaps death or disability. Compared to risks that won’t cause significant harm or are reversible, but have a much higher chance of happening.

Risks are difficult to grapple with – as doctors, we find it difficult, too. You may know that you’re a person who prefers graphs or representations on diagrams. Ask your doctor if there are graphics are available. Give yourself time to digest important decisions, and give your doctor time, perhaps in a follow-up appointment, to find a way of explaining so makes sense to you for any decision you need to make.

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Dr Roger Henderson
Reviewed by Roger Henderson
Reviewed on 29.04.2024
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