Lesson 2: Measurement (1) Case Definition and Measures

Overview Section

Epidemiologists ask “Who gets the disease? In what frequency? Is the frequency changing over time? How does the frequency in one population compare to the frequency in another population?” Answering such questions first requires a case definition. Second, we then need measures to estimate disease frequency. Third, we may want to compare measures in different populations.



Coggon, D., G. Rose and DJP Barker. "Quantifying disease in populations" in Epidemiology for the Uniniated. Fourth Edition. BMJ Collection. http://resources.bmj.com/bmj/readers/readers/epidemiology-for-the-uninitiated/2-quantifying-disease-in-populations 20 Jan 2011.


Upon completion of this lesson, you should be able to:

  • Define a case for epidemiologic purposes;
  • Select and use measures of disease frequency;
  • Calculate prevalence and incidence from surveillance data;
  • Define point prevalence, period prevalence, cumulative incidence, and incidence density