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Stratified Sampling

Related Terms: Strata

The process of dividing a population into mutually exclusive subgroups (strata) and taking random samples from each subgroup rather from the whole population. Can be used when the population being studied is heterogeneous but may be categorized into relatively homogenous subgroups by certain characteristics if samples were drawn from the population as a whole.

Example

In a research study investigating the association between smoking and the risk of lung cancer, the researchers suspect that gender is related to the risk of smoking and cancer. To ensure that there are enough males and females to evaluate the relationship, the study divides the population into males and females. Males and females are then sampled separately. Then the association between smoking and cancer are assessed within each group.

Further Reading

Last, J. 1983. A Dictionary of Epidemiology, New York, NY: Oxford Medical Publications.

Kleinbaum, D., L. Kupper, and H. Morgenstern. 1982. Epidemiologic Research: Principles and Quantitative Methods, Belmont, CA : Lifetime Learning Publications.

University of Glasgow. Statistics Glossary. Available at http://www.stats.gla.ac.uk/steps/glossary/alphabet.html .