Research in Brief: Randomized Controlled Trials

NARIC’s Research In Focus series highlights new and interesting findings from NIDILRR-funded studies, presented in lay language summaries. The series covers a wide array of topics and aims to present peer-reviewed research in readable formats, so our readers can learn about issues that affect them every day. The Research in Brief companion series breaks down some of the concepts readers might come across when exploring research in disability and rehabilitation. This issue introduces the concepts of randomized clinical trials, placebo, bias, and blinding.

When you’re reading through scientific research, you may find yourself wondering how researchers decide which study design to use to answer their question. This post will highlight one of the most commonly used scientific study designs and its advantages and disadvantages: The randomized controlled trial.

When scientists are preparing a study, their decision comes down to the research question they want to explore. The gold standard for research on medications and interventions is randomized controlled trials (RCT). This is a rigorous study design that gives scientists a look at the effectiveness of a specific treatment or intervention.

Here’s how it works. Scientists randomly put their study participants into two groups. The key here is that both groups should be as similar to each other as possible: similar age ranges, health status, etc. One group is then given a specific treatment, while the second group is given either no treatment or a placebo (a type of treatment or drug that is similar in appearance to the actual drug but has no physical effect). For example, if researchers wanted to know whether a specific drug was more effective at reducing blood sugar in patients, they may give half their participants their test drug while the other half are given the standard (old) treatment or a placebo.

Let’s say that the researchers followed both groups for three months and found that their test drug significantly reduced their patients’ blood sugar when compared to the group using the old treatment. Because both groups are similar, the researchers can confidently make the deduction that the results they are seeing are based on the new drug itself and not another factor. So, doctors can advise a new treatment plan based on these results.

One thing researchers need to look out for while conducting RCTs is that they don’t introduce bias. Bias is when the results are skewed one way or another due to either the researchers’ or the participants’ assumptions. Going back to our example, what if the researchers inadvertently divided the groups based on what time participants showed up to their office? In this scenario, participants that arrived before 12 pm were placed in the treatment group and those that arrived in the afternoon were placed in the placebo group. While this may seem random, it could also introduce some form of bias. It’s possible that the participants arriving during the day were those who worked remotely and generally had more time to exercise during the day. Meanwhile, the participants in the placebo group worked in an office and came to the researcher’s office instead of going to the gym in the afternoon. Without realizing it, the researchers may have completely overlooked an important variable that could skew the results they were observing.

To reduce bias, researchers rely on statistical measures to randomly assign participants into groups. Researchers also practice blinding. Blinding in RCTs is used to reduce bias from both the researchers and participants. A single-blind study is one where participants are not told whether they are receiving the treatment or the placebo. A double-blind study is one where both the researchers and the participants are not aware of whether the participant is in the treatment or the placebo group. For example, the participants are assigned a number and a group through a random number generator on the computer. While some of the researchers may have this information, they won’t share it with the specific researchers that are in charge of taking data and conducting interviews with the participants. Therefore, the researcher who is interacting with the participants can observe and take notes without their own bias getting in the way. 

The strict rules of randomization and blinding for RCTs are what makes them a gold standard for research. However, these same rigorous standards are also what can make RCTs difficult to conduct, time-consuming, and very expensive. This makes RCTs not ideal for all research questions.

The Research In Focus series has featured several examples of RCTs that studied interventions to improve the health, function, and independence of people with disabilities, including:

Hafsa Abdirahman MPH is a public health scientist and freelance medical writer and editor. She believes that access to evidence-based, quality health information can save lives and she’s worked throughout her career to put this belief into practice.

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