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What is a randomised controlled trial?

Transcript of the film 'The Gold Standard: What are randomised controlled trials?'.


Randomised controlled trials (RCTs) are a type of clinical trial. RCTs aim to make a fair comparison between a new treatment and the existing treatment, or between two (or more) existing treatments, to see which one works best.

A controlled trial compares two or more groups of people: one or more experimental group(s) who receive a new treatment, and a control group, who receive the current standard treatment (which might be the best existing treatment, no treatment or a placebo). Information from the follow-up of the control group allows the researchers to see whether the new treatment(s) they are testing are any more or less effective than the existing treatment.

The decision about which treatment each participant in a randomised controlled trial receives is made at random – based on chance, rather than decided by the doctor or participant. This process is called randomisation.

Randomisation ensures that the two (or more) groups of people in a trial are as similar as possible, except for the treatment they receive. This is important because it means that researchers can be sure that any differences in outcomes between the groups are therefore only due to the treatment received.

Randomisation is the best way of ensuring that the results of trials are not biased by the way participants in each group are selected. For example, if a doctor chose which treatment a patient should receive as part of a trial, she or he might give the new treatment to sicker patients, or to younger patients. This would make the results of a trial unreliable, as it could exaggerate or hide the effects of the treatment.

Randomised controlled trials are the most reliable way to compare treatments.



For more information about clinical trials, try our section on How do we make sure a trial is safe?

On Wednesday 20 May 2015, we held a Twitter Q&A for International Clinical Trials Day on the theme: 'Why Do Clinical Trials Matter?'.  To learn more about clinical trials, and to read what our panellists had to say on the subject, have a look at our 'Storify' of the event. 

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