What Is Random Selection?

Rob Friedman / Getty Images

When researchers need to select a representative sample from a larger population, they often utilize a method known as random selection. In this selection process, each member of a group stands and equal chance of being chosen as a participant in the study.

How does random selection differ from random assignment? Random selection refers to how the sample is drawn from the population as a whole, while random assignment refers to how the participants are then assigned to either the experimental or control groups.

It is possible to have both random selection and random assignment in an experiment. Imagine that you use random selection to draw 500 people from a population to participate in your study. You then use random assignment to assign 250 of your participants to a control group (the group that does not receive the treatment or independent variable) and you assign 250 of the participants to the experimental group (the group that receives the treatment or independent variable).

Why do researchers utilize random selection? The purpose is to increase the generalizability of the results. By drawing a random sample from a larger population, the goal is that the sample will be representative of the larger group and less likely to be subject to bias.

Examples and Observations

"Essentially, we chose at random geographic areas of the country, using the statistical equivalent of a coin toss to select them.

Within these geographic regions, we randomly selected cities, towns, and rural areas. Within those cities and towns, we randomly selected neighborhoods. Within those neighborhoods, we randomly selected households. If there were two people living in a household who were in our age range, we flipped a coin to select which one to interview.

If there were three people in the household, we did the equivalent of flipping a three-sided coin to select one of them to interview."
(Michael, R., 1994)

"Very small samples are less likely to be representative of the population because even random selection can yield a limited or biased sample if the sample size is very small. An unusual member of a small random sample can have unfortunate effects even when that individual was selected at random. Thus, a large random sample is likely to yield a more externally valid representation of the population than is a small one. Large sample dilute the effect of having selected an unusual individual."
(Elmes, Kantowitz, and Roediger, 2012)

More Psychology Definitions: The Psychology Dictionary


Elmes, D. G., Kantowitz, B. H., & Roediger, H. L. (2012). Research Methods in Psychology. Belmont, CA: Wadsworth.

Hockenbury, D. H. & Hockenbury, S. E. (2007). Discovering Psychology. New York: Worth Publishers.

Michael, R. T. (1994). The National Health and Social Life Survey: Public Health Findings and Their Implications. In S.L. Isaacs & J. R. Knickman, eds. To Improve Health and Health Care: 1997. San Francisco: Jossey-Bass Publishers. 1997: 232-250.

Continue Reading