What is a Randomized Experiment?
A randomized experiment involves randomly splitting a group into smaller groups: one group (the treatment group) receives the intervention, and one does not (the control group). The researcher selects the assignment mechanism, which is also random. Care is taken to choose a sampling method that results in an equal chance of each participant receiving the treatment. Another distinguishing feature is that the experiment must involve the manipulation of some kind of treatment by the researcher (a “variable of interest”) .
Randomized experiments are used extensively in a wide variety of agricultural and biological experiments, including human clinical trials. They are also, less commonly, seen in other fields such as economics.
Randomized Experiment Stages
The experiments are usually conducted in two stages :
- Selection of a small sample of participants from a larger population, using a random sampling technique. This step ensures that the results will have external validity.
- Random assignment to treatment and control groups. This step ensures that the observed effects have internal validity.
Benefits of Randomized Experiments
Using randomization has several benefits :
- It prevents selection bias and accidental bias, as well as bias in treatment assignments.
- Homogeneous, comparable groups are created.
- Probability methods, including hypothesis tests, can be used to ensure the results didn’t happen by chance.
 World Bank. Randomized Experiments. Retrieved December 29, 2021 from: http://web.worldbank.org/archive/website01397/WEB/IMAGES/EXPERI-2.PDF
 Munck, G. & Verkuilen, J. (2005). Research Designs. In Encyclopedia of Social Measurement, Pages 385-395.
 Suresh, K. An overview of randomization techniques: An unbiased assessment of outcome in clinical research. J Hum Reprod Sci. 2011 Jan-Apr; 4(1): 8–11.