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Experimental studies. What is a randomised, double-blind, placebo-controlled trial?

Experimental studies. What is a randomised, double-blind, placebo-controlled trial?

You must acquire the habit of reading research papers because they are the sources of all the policies that govern your life. You should understand when you come across experimental studies titled ‘randomised, double-blind, placebo-controlled trials.’

We’ve discussed observational studies in the previous article; their major drawback is bias. Experimental studies aim to reduce such bias. Unlike observational studies, experimental studies involve an active intervention. On various occasions, experimental studies have at least two groups of participants. One of the groups is always a control group.

A control group receives no intervention. When such intervention is an investigational new drug, the control group doesn’t receive the drug under investigation. It gets a solution or tablet which, is similar in shape, size, and weight but with no active ingredients. We call this a placebo. In other scenarios, investigators may wish to follow a group of patients with a specific disease receiving medication. They pit them against a similar group of patients who don’t receive the drug but continue getting conventional therapy. For that matter, the latter becomes the control group. Control groups are crucial to concluding. We use them to ascertain the feasibility of the interventions under investigation. When we include a control group, we term it a controlled trial. If, on the other hand, researchers provide an intervention but with no control groups, it becomes an uncontrolled trial.

For any study, every member of the population has an equal opportunity to enter a trial. We call it a random chance (probability). Investigators set the formula of recruiting the participants such that everyone enters a category by chance. We term this randomisation. For that matter, it is a randomised trial. Investigators never recruited participants basing on their blood relations or the size of their pockets.

For several interventions, the researchers conducting the study and the participants may or may not be aware of the type of intervention, say which of the tablets contains an active ingredient and which one is the placebo. We term this blinding. When both the researchers and participants are unaware of the intervention, the trial is double-blinded. When the researchers, but not the participants aware of the intervention, it is s single-blinded trial. In other words, it is blinded to the participants. When both parties know the intervention, it becomes an open-label trial.

Experimental studies take on different formats. Some occur with concurrent controls, implying that both the study participants and controls enter the trial simultaneously. In such scenarios, a participant cannot be in both groups. Other studies occur with self-control groups. In this case, the study participants are both a treatment and control group. The researchers collect data from the participants before and after they have received the intervention.  An example of such a study is the cross-over trial. More still, a trial can occur with external controls: researchers compare the interventional group to a group outside the study, a historical control.


Observational studies. Is it a cohort, case series, or cross-sectional study?

With the above information, does a randomised, double-blind, placebo-controlled trial make sense to you? If not, in such a study, researchers recruit participants in a random but organised format. Both the researchers and participants are unaware of the intervention under investigation. The intervention has two arms, an active one and a placebo, so it’s controlled in a way that the principal investigators are monitoring the outcomes of those receiving an active ingredient and those who are not. Those receiving no intervention are the control group.

For more information about experimental studies, enrol for an epidemiology course via Coursera. Click here to join. In our next article, we briefly discuss a meta-analysis and a systematic review.


Dr A. M. Ssekandi is a medical officer, researcher, content creator, author, and founder of He does private practice with a public touch. He is a certified digital marketer. He has earned certificates in Understanding Clinical Research and Writing in Sciences from the University of Cape Town and Stanford University respectively. He also has a certificate of Good Clinical Practice from

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