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Before a new drug or therapy can reach patients, researchers and regulatory agencies need evidence that it is safe and effective. One of the most reliable ways to gather this evidence is through a randomized controlled trial (RCT).
A key challenge in medical research and therapy development is that symptoms can vary widely between people and often change over time. People may improve or worsen for reasons unrelated to the treatment being studied, and expectations can influence how someone experiences their symptoms. An RCT is a structured way to account for these natural changes and other factors, helping researchers determine whether a treatment is making a real difference for patients.
A clinical trial is a systematic study of a treatment, such as a drug or surgical procedure, in humans. Researchers follow a predefined plan to figure out how people respond to the treatment over time.
A trial is controlled when it includes at least two groups:
Without a control group, researchers cannot tell whether the improvements they observe are due to the treatment they are studying or simply due to natural fluctuations in symptoms, participants’ expectations, or other factors.
A trial is randomized when participants are assigned to groups by chance. Randomization helps ensure that the groups are as similar as possible, so any differences at the end of the trial are more likely to be caused by the treatment rather than by differences in the makeup of the groups.
For example, in a clinical trial for a new treatment, a research team might assign participants to either the treatment or control group using a computer-based method like a random number generator or a digital coin flip. Participants, and often even the researchers, do not know who is in which group until the study ends, to reduce the influence of expectations on the results. This process is called “blinding”. The researchers will also do their best to balance the groups based on key characteristics that could affect the results, such as age and symptom severity. If, by the end of the trial, the group that received the new treatment shows a greater reduction in symptoms than the control group, the researchers can be confident that the treatment caused this improvement.
Figure 1. Structure of a randomized controlled trial, where participants are randomly assigned to receive either the new drug under investigation (treatment group) or a placebo (control group). Outcome measures are compared between groups to determine the effects of the investigational drug. Figure created by Dr. Chloe Soutar using BioRender.com.
Imagine a research team is testing a new medication to improve coordination and balance in adults with ataxia. The researchers recruit 200 adult men and women to participate in the clinical trial. Each participant is randomly assigned to one of two groups:
The groups are balanced in terms of average age, symptom severity, and disease history, and participants do not know which pill they are given. All participants take their assigned treatment once daily for six months and complete the same coordination and balance tests at the beginning and end of the treatment period. Neither the participants nor the researchers know who is receiving the new medication or the placebo. If Group A shows significantly greater improvement in coordination and/or balance than Group B after the six-month treatment period, the researchers can attribute that difference to the new medication.
RCTs are considered the gold standard in medical research because they allow us to distinguish real treatment effects from chance and other variables. The structure and rigor of RCTs make them far more reliable than simply observing whether people seem to improve after taking a new treatment. Because of this, understanding whether a “promising” treatment for ataxia—or any other condition—has been tested in an RCT can help you judge the evidence for its benefits and gauge how close it may be to becoming widely available.
If you would like to learn more about Randomized Controlled Trials, take a look at these resources by Nesta and the Decision Lab.
Snapshot Written by:Chloe Soutar, PhD
Edited by:Katie Deschamps, PhD
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