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Absolute risk

This is a way of describing the chance of something happening. For example, the risk of something happening may increase by 5% to 6% - the absolute risk would be 1%. It is often confused with relative risk.


Something happening quickly 

Antibiotic resistance

When a bacteria is able to survive even when treated with certain antibiotics.


The relationship between two things, for example, earning more money is associated with living longer.  It is often confused with causation.


Cardio pulmonary resuscitation. This is used when a person is unconscious and has no pulse, to try and restart the heart. The chest is pressed up and down. The mouth may be opened, and the rescuer breathes into the persons mouth.

Care plan

A document where a persons’ needs and values are written along with a plan to meet them.


 When one thing causes another thing, for example, a faulty wire causes a fire.  It is often confused with association.


lasting for a long time, possibly forever.

Clinical trials

Clinical trials examine the effects of different medicines, operations, psychological treatments, physiotherapy or other kinds of treatment to find out if they work, how well they work, and what and who they work for. There are many different types of trials, which can be described as ‘fair tests’. Find out more.


Do Not Resuscitate

Diagnostic Tests

Tests that are done to work out if someone does or does not have a health condition. The results are not always clear and usually need careful consideration.

False negatives

When a test does not diagnose you with a disease or disorder but there really is a problem. The test result is wrong.

False positives

When a test wrongly shows that a condition or disease is present.


Legal term for an adult or child who looks after the rights of someone who does not have ‘capacity’ or ability to make decisions for themselves.


Usually means a treatment or test that needs to go inside the body, or a condition like cancer which has spread through tissues.

Lead time bias

When a condition is diagnosed earlier but does not increase the length of a person’s life. It can sometimes make some types of early diagnosis look better than it is.


National Institute for Health and Care Excellence.


The Number Needed to Harm. If the NNH was 10, then 10 people would be treated and one would be harmed.


The Number Needed to Treat. If the NNT was 10, then 10 people would have to be given the treatment for it to work for one person.

Nocebo effect

The opposite of a placebo effect, when a placebo appears to give side effects rather than benefits.

Observational studies

When a group of people are observed to find out what happens to them over time, without trying to change the group by giving them something different.


A result, which can be good or bad - like an improvement in being able to walk, or having more pain.


When people are diagnosed with a condition but don’t get any advantage from that information.

Palliative care

When the treatment is designed to improve the quality of life of the person. It is important to know that palliative treatment can be started a long way from when death is expected.


A rare condition which people are born with, and where eating certain foods causes brain damage. This can be avoided by a special diet.


Placebos are used in research to try and work out how good a treatment is. We know that many conditions improve no matter what the treatment is. Using a placebo - something that looks like a ‘real’ treatment but isn’t - means that we can work out what the treatment is really doing.

Power of attorney

 A legal document which people make in order to allow a trusted person to make decisions for them. It can be used if the person becomes too unwell to make the decisions themselves in future. There are different types of powers of attorney for different kinds of decisions, related to health or finances.

Press releases

These are issued by medical journals, universities, research companies, and commercial companies and sent to TV, radio and newspapers, in order to attract attention to their work. Some press releases try and explain difficult concepts so that the media coverage is correct. Some press releases overhype the claims. NHS Behind the Headlines often investigates these kinds of stories. 

Primary prevention

To try and stop something from happening in the first place, for example, to use medication to lower blood pressure, in order to reduce the risk of a heart attack.

Proxy marker

t can be hard to do big studies over a long time. Researchers may want quicker answers. For example, if a drug has been developed to prevent dementia, it will take a long time to know if it helps, because dementia usually takes years to develop. A 'proxy marker' might be used instead, for example, like brain changes on scans that many people who later develop dementia have. This isn’t as reliable as waiting to find out how many people develop dementia.

Qualitative studies

This is a type of research which finds out what people think about their experiences, for example of receiving care in hospital.

Randomised controlled trial

These is a test where groups of people are randomly divided and given different types of treatment, then monitored to see the difference between the two. This can help to understand what treatments are best or what treatments are harmful. Randomised controlled trials can be 'single blind' (where the participant doesn’t know what treatment they are having) or double blind (where neither the participant nor the researcher knows what treatment is being used). These are usually the most reliable types of trial.

Relative risk

This is a way to describe chance, measured in proportion to another chance. For example, a drug might cut the risk of a heart attack by 50%. To understand what this means for us, we have to know what our risk was to start with. So, for example, if we had a risk of a heart attack of 60%, the drug could cut the risk to 30% (half of 60%). But if we had a risk of 2%, the drug would cut the risk to 1% (half of 2%).


This means that people who believe themselves to be well have tests to find out if they are at risk of particular conditions. If someone has a symptom, screening tests are not applicable - they are only for people with no symptoms.

Secondary prevention

To try and stop something from happening again, for example, if someone has had a stroke, secondary prevention aims to stop another stroke from happening.


Another term for placebo, but often used to describe ‘sham surgery’ when patients either have a ‘real’ operation or a procedure that feels and looks like a real operation but isn’t.


When people feel something is wrong, for example, a fever, a cough, and muscle aches can be symptoms of the flu, or a breast lump might be a symptom of cancer. Symptoms are felt by the person having them.

Systematic reviews

A way of searching through all the research on a subject, looking carefully for research that hasn’t been published in medical journals or isn’t obvious. This is usually a good way of making sure that all the research is weighed up before judging whether treatments work or not.