The process by which participants in clinical trials are assigned by chance (randomly) to separate groups (see Arm), which will receive different interventions. Neither the researcher nor the participant can choose the intervention assigned to the group. By randomly assigning the participants to the intervention groups, the comparison between the intervention effects are fairer, because the groups are similar, according to the characteristics of the patients or of the disease – both known and unknown. The only difference consists in the administered interventions. Therefore, at the end of the clinical trial, any difference which should emerge in terms of efficacy and toxicity, in favour of one particular intervention, can be attributed exclusively to that particular intervention and not to pre-existing differences among the groups.
