Post 6: Randomised and Non-randomised Control Trials

A Randomised Control Trial (RCT) is a specific trial in which individuals are randomly assigned to a group in which they receive treatment or are assessed. It is a controlled trial because there are 2 groups, the treatment and the control group¹. The RCT is considered to offer the most reliable evidence because processes used during the conduct of the RCT minimises factors that can affect the results².  These processes include employing strict inclusion or exclusion criteria, intended to maximise the validity of the study.  This produces comparable groups resulting in minimising the threat of confounding as any differences can be attributed to the intervention¹.  To minimise bias further, blinding can be used, that is, eliminating critical information on allocation of treatment from either patient, observer or evaluator of the study³.  This ensures that there are no differences in the way either group is assessed or managed and that the intervention or placebo treatment appears the same.

 Click on the video above to take a more detailed look at Randomised Control Trials

When an act of random allocation may reduce the effectiveness of the intervention or a trial may be considered unethical, it may be appropriate to use a non-randomised trial design.  While similar to a RCT in that it compares at least two interventions, selection bias poses a significant threat to the validity of the trial as the participants are not randomly allocated to groups, rather carried out using selection processes.

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1 Gerstman B.  Epidemiology kept simple: An Introduction to traditional and modern epidemiology.   3rd ed. Hoboken, USA: Wiley; 2013.

2  Akogbeng A.  Community child health, public health and epidemiology:Principles of evidence based medicine. Arch Dis Child. 2005; 90:837-840

3  Altman DG. Randomisation.  BMJ 1991; 302:1481-2