The NICE Glossary provides brief definitions and explanations of terms used on our site. The terms describe how we work and how our guidance is produced.
Our glossary excludes specific clinical and medical terms. If you cannot find the term you are looking for, please email us so that we can consider adding it to the glossary.
Some definitions and examples are based on those in the 'HTAi consumer and patient glossary', with thanks to Health Technology Assessment International.
Whether a test or study actually measures what it aims to measure. Internal validity shows whether study or test is appropriate for the question, for example whether a study of exercise among gym members measures the amount of exercise people do at the gym not simply whether people join. External validity shows whether findings can be generalised to other settings or populations.