An experiment in which two or more interventions, possibly including a control intervention or no intervention, are compared by being randomly allocated to participants. In most trials one intervention is assigned to each individual but sometimes assignment is to defined groups of individuals (for example, in a household) or interventions are assigned within individuals (for example, in different orders or to different parts of the body).

See Randomised Control Trials video course by Healthknowledge.org.uk

Randomization: Use of a probability scheme for choosing a sample. This can be done using random number tables, computers, dice, cards, and so forth (CDC evaluation glossary).