Types of Trial Design

In non-randomised controlled trials, participants are allocated into treatment and control arms by the investigator. It is appropriate to use a non-randomised controlled trial design when the act of random allocation may reduce the effectiveness of the intervention.

Non-randomised controlled trials have the potential to study two groups that are not strictly comparable. However, there are different types of controls that can be used in non-randomised trials:

• Control groups can be concurrent controls or historical controls.
  

When using a historical control, all participants in the trial receive the study medicine; the results are either compared to the patient’s history (for example, a patient living with a chronic illness) or a previous study control group.