Randomized controlled trial

About the “What researchers mean by...” series

This research term explanation first appeared in a regular column called “What researchers mean by…” that ran in the Institute for Work & Health’s newsletter At Work for over 10 years (2005-2017). The column covered over 35 common research terms used in the health and social sciences. The complete collection of defined terms is available online or in a guide that can be downloaded from the website.

Published: October 2012

In a researcher’s toolkit, the randomized controlled trial (RCT) is one of the best ways to produce valid evidence on the effectiveness of interventions, from prevention programs to treatment options. According to the established hierarchy of evidence, the most valid evidence from original research comes from RCTs, followed by cohort studies and then case control studies. Indeed, RCTs are often said to be the "gold standard" for generating reliable evidence.

Here’s how RCTs work. Study participants are deemed eligible through a recruitment process that involves specific criteria for inclusion and an informed consent process.

Those eligible are randomly assigned, in a process that’s not unlike flipping a coin, into one of two groups or ‘arms’ of the study: (1) the intervention group, or (2) the control group. The first group receives the intervention being studied, which could be a new treatment or procedure. The second does not, and instead receives an inactive placebo, conventional treatment or nothing at all.

The cornerstone of RCTs is this: Because the allocation process is random, it minimizes the chance that people who received treatment and those who did not had different characteristics. In other words, with random allocation, any differences in outcomes between the intervention group and the control group can be attributed to the intervention, as opposed to any of the participants’ attributes like age or disease.

An RCT in action

Let’s say you’re a scientist interested in non-medicated pain relief for fibromyalgia. Does acupuncture help? An RCT has already been conducted to answer this question.*

In the recruitment phase of this study, the research team sought to enlist female patients between the ages of 20 and 70 years diagnosed with fibromyalgia according to the 1990 American College of Rheumatology classification criteria. To be included in the study, patients needed to have reported moderate to severe pain intensity and to be using antidepressants.

In the study, 58 women with fibromyalgia were allocated randomly to receive either: (1) acupuncture with tricyclic antidepressants and exercise, or (2) tricyclic antidepressants and exercise only. Patients rated their pain on a visual rating scale, and quality of life was also evaluated using a blinded assessor (i.e. the researcher assessing the results).

At the end of 20 sessions, patients in the RCT who received acupuncture had significantly less pain than the control group. This study concluded that the addition of acupuncture to usual treatments for fibromyalgia may be beneficial for pain and quality of life for three months after the end of treatment.  

This conclusion would not have been possible without the use of an RCT. Its random allocation process is one of the best ways to secure valid evidence.

*See "A randomized controlled trial of acupuncture added to usual treatment for fibromyalgia" in the July 2008 issue of Journal of Rehabilitation Medicine (Vol. 40, No. 7, pp. 582–588).

Source: At WorkIssue 70, Fall 2012: Institute for Work & Health, Toronto