IATE Term of the Week: Randomisation


In times of COVID-19 pandemic, the health system has gained a primary spot in our lives. Clinical trials to create vaccines against COVID-19 have been widely discussed and have become part of everyday conversations in non-medical settings. However, when it comes to clinical trials, many might not be familiar with their fundamental principles. One of these principles is “randomisation”.

Randomisation is the process that, more or less by chance, allocates participants to clinical trials into separate groups that are administered different treatments. The most basic randomisation has patients split into an investigational group, which is given the experimental drug or treatment, and a control group, which is given the standard treatment or a placebo.

The essential steps of randomisation are:

  1. collection of patient information
  2. random assignment of each patient to a group, done by a computer
  3. start of the clinical trial in which the control group receives the standard treatment, while the investigational group receives the new treatment

The importance of randomisation in clinical trials

Randomisation in clinical trials allows eliminating, or at least limiting, biases in research studies. Avoiding biases is a fundamental challenge of research in any field. Regarding the medical field, biases can occur when selecting participants for a study, and later on, while the study is being carried out. Avoiding biases means that the trial should not be influenced by human factors such as preference for a certain treatment over the other, but only by statistical rules.

To avoid biases, randomisation must be paired with “blinding”, the situation in which neither the patients nor the medical staff involved in the study know which patients are administered which study drug or treatment. This practice aims at eliminating biases in the analysis of the results of the study.

IATE Randomisation 2
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3 types of randomisation

The most basic type of randomisation is “simple randomisation”, in which patients are allocated completely randomly to the study groups. The downside of this method is that it can create inequalities in the sizes of the study groups. If the sample for the study is small, then such unbalance can produce data that is not comparable. For this reason, simple randomisation is used in trials with a high number of participants. In some types of trials, simple randomisation can be too uncontrolled for the goals of the study. Two types of controlled randomisation are “restricted randomisation” and “stratified randomisation”.

Restricted randomisation consists in using a method to randomly assign the same number of participants to each group. The methods can vary and influence only the size of the groups. When certain characteristics of patients need to be taken into account, participants are selected through stratified randomisation. In this type of randomisation, the study groups are formed according to characteristics such as sex, age, gravity of the disease and others.

If you are interested in terms related to the COVID-19 pandemic and the medical field, check out our articles about COVAX Facility and self-test!


Cancer.gov. 2021. Clinical Trial Randomization – National Cancer Institute. [ONLINE] Available at: https://www.cancer.gov/about-cancer/treatment/clinical-trials/what-are-trials/randomization/clinical-trial-randomization-infographic. [Accessed 01 July 2021].

Cancer.gov. 2021. No page title. [ONLINE] Available at: https://www.cancer.gov/publications/dictionaries/cancer-terms/def/randomization. [Accessed 01 July 2021].

EMEA. 1998. Statistical Principles For Clinical Trials. ICH Harmonised Tripartite Guideline. ICH Topic E 9. Statistical Principles for Clinical TrialsNote For Guidance On Statistical Principles For Clinical Trials (CPMP/ICH/363/96). [ONLINE] Available at: https://www.ema.europa.eu/en/documents/scientific-guideline/ich-e-9-statistical-principles-clinical-trials-step-5_en.pdf. [Accessed 01 July 2021].

Hoare, Z. 2010. Randomisation: what, why and how?, Significance, 7(3). doi: https://doi.org/10.1111/j.1740-9713.2010.00443.x


Written by Maria Bruno, Schuman Trainee at the Terminology Coordination Unit. She holds a master’s degree in Translation and a bachelor’s degree in Italian Language and Literature. She is trained in websites and social media management, content writing and SEO. Currently, she is studying for her Diplôme Universitaire in Terminology at the University of Savoie-Mont Blanc.