The proportion of a chosen population that are affected by a single disease.

The extent to which an individual can work effectively.

A protocol is the plan for a piece of research. It usually includes information about:

• what question the research is asking and its important / relevance
• the background and context of the research, including what other research has been done before
• how many people will be involved
• who can take part
• the research method
• what will happen to the results and how they will be publicised.

A protocol describes in great detail what the researchers will do during the research. Usually, it cannot be changed without going back to a research ethics committee for approval.

Qualitative research is used to explore and understand people's beliefs, experiences, attitudes, or behaviours. It asks questions about how and why a "quality" is being measured by the research. Often the term "holistic" is used, meaning that the complexities of human behaviour are preserved in the study. Qualitative research might ask questions about why people want to stop smoking. It would not ask how many people have tried to stop smoking. It does not collect data in the form of numbers. Qualitative researchers use methods like focus groups and interviews.

A numerical measurement that combines quality of life and life expectancy.

A numerical measurement that combines quality of life and life expectancy

In quantitative research, researchers collect data in the form of numbers. So they measure things or count things a "quantity" is being measured. Quantitative research might ask a question like how many people visit their GP each year, or what proportion of children have had an MMR vaccine, or whether a new drug lowers blood pressure more than drugs that are usually used. Quantitative researchers use methods like surveys and clinical trials. 

Randomisation randomly assigns patients to a control group or treatment group in clincial trials. It removed bias from trials, which could make the test unreliable.

The EU defines a condition as 'rare' if it affects less than 1 in 2000 people.

Groups of professionals and service users who review the ethical considerations of research studies.