What Is Randomization?

Looking for the full method? Read the detailed guide: Randomized Controlled Trials Explained.

Randomisation (randomization) is the use of chance to assign participants to study groups, so that known and unknown characteristics are, on average, balanced between groups. It is a core feature of randomised controlled trials.

Example

Invented for teaching: A computer generates a random sequence in blocks, and participants are assigned to the intervention or control group in that order, with the allocation hidden from the person enrolling them.

Common misunderstanding

Randomisation is not the same as random sampling. Random sampling selects who is in the study; randomisation assigns those already in the study to groups. Randomisation also does not guarantee identical groups, particularly in small trials; it removes systematic bias in assignment.

Learn more

See Randomized Controlled Trials Explained.

This page is general educational information about research methods. It is not medical, legal or regulatory advice; follow your institution's ethics board and your target journal's instructions.