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Study Base

Lead Author(s): Jeff Martin, MD

Definition of a Study Base

A study base, also called a reference population, is a defined population whose disease experience during some period of time is the source of the study data.

  • This population gives rise to cases
  • Defined before cases appear by a geographical area or some other identifiale entity like a health delivery system or a cohort study.
Identifying the study base answers the question: What population gave rise to the disease diagnoses in the study?

Understanding the study base concept provides the clearest guidance to understanding valid case-control design, the study design that is most often a cause of confusion.

The phrase study base was first used by the epidemiologist Olli Miettinen, who is one of the main theorists of current epidemiological thinking. Others have proposed different language, the most common alternative probably being the phrase used in Szklo and Nieto, reference population, or in some other texts, referent population.

Primary and Secondary Study Bases

Primary versus Secondary study base differ in how they identify the source of the cases and controls.

Primary study base case-control studies can be very strong design

  • Important, under-emphasized aspect of case-control design
Secondary study base often not explicitly recognized by researchers
  • Even when recognized is still source of many bad case-control studies
This is a crucial distinction that explains a lot of weak case-control studies that have reaching erroneous conclusions and given case-control design a bad name in many circles.

Study Base by Study Type

The study base is the population who experienced the disease outcomes you will observe in your study.

  • In a Cohort Study, the study base is an explicitly defined cohort.
  • In a Cross-Sectional Study, the study base is a hypothetical cohort sampled at one point in time.
  • In a Case Control Study, the study base is the cohort, either explicit or hypothetical, that gave rise to the cases and continues to recruit new subjects during the time period of the study..


Szklo, M., & Nieto, F. (2007). Epidemiology: Beyond the Basics (2nd Edition ed.). Boston: Jones and Bartlett Publishers.

Topic revision: r14 - 02 Jun 2009 - 15:57:55 - MaryB?

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