Introduction

Generally in a randomised controlled trial, study participants are randomly assigned or randomised to one of two groups: the experimental group receiving the intervention that is being tested and the comparison group (control) which receives a conventional treatment or placebo. These groups are then followed prospectively to assess the effectiveness of the intervention compared with the standard treatment or control.

Randomisation (if done properly) ensures no systematic differences between the intervention group in factors, known and unknown, that may affect the outcome.