Internal Validity

Internal validity in a clinical trial is the ability of the trial to reach the correct conclusion about whether or not, and to what extent, a treatment is causing a measured effect on the participants. It implies accurate and unbiased measurement of that effect.

Internal validity is achieved when possible alternative explanations for the measured effect can be excluded, such as chance or bias. Well-designed clinical trials take this into account, for example by using randomisation and blinding.

» Glossary