15 January 2019 - Over the past 5 decades, the randomised clinical trial has become the gold standard for evaluation of the risks and benefits of new interventions, including drugs, medical devices, and surgical procedures.

To justify the use of randomisation, it is important to note that in a non-randomised study comparing two interventions, a small P value (of which P < .05 is generally considered statistically significant) for a statistical comparison between groups can be due to 1 of 3 sources: chance, causation, or confounding.

Because randomised assignments cannot be associated with participant characteristics, effective randomisation eliminates the third possibility, enabling direct assessment of potential causal relationships provided that the study is designed, conducted, and analysed properly.

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