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Randomisation is a way of preventing bias in research, and so helps make sure that the research results are valid.  Patients taking part in the trial are chosen randomly by computer to take either the new drug or the standard treatment, with an equal chance of being chosen for either.

A phase 2 trial might use randomisation to compare two different ways of giving the same treatment.  As an example, in a trial of a new tablet, after randomisation half the patients would be asked to swallow two tablets in the morning, the other half to take one tablet in the morning and one in the evening.  Randomisation is also used in placebo-controlled trials.