Lesson 3: Measurement (2) Exposure Frequency; Association between Exposure and Disease; Precison and Accuracy

Overview Section

In Lesson 2, we saw that the case definition can have great impact upon results and the interpretation of results. We also examined prevalence and incidence. We measured the frequency of a disease, specifically looking at 5 different ways: count, proportion, ratio, rate and risk. Each of these can be useful depending on the purpose and the study design.

In Lesson 3, we are now going look at whether or not a particular exposure is associated with increased risk or occurrence of disease, and issues related to this process and quality of that association.. This is going to begin with a definition of exposure and the process of measuring that exposure. 


Sexton K; Kleffman DE; Callahan MA. Journal of exposure analysis and environmental epidemiology, (1995 Jul-Sep) Vol. 5, No. 3, pp. 229-32. Ref: 9 Journal code: 9111438. ISSN: 1053-4245.


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

  • Use the terminology of exposure, effect and association in accordance with epidemiologic practice;
  • Apply a definition of exposure to an environmental contaminant;
  • Recognize potential effect modifiers in a pathway between exposure and disease;
  • Develop appropriate questions to assess the level of exposure and relationship of exposure to outcome;
  • Differentiate between update and intake;
  • Describe advantages and disadvantages of direct monitoring;
  • Identify strengths and weaknesses of 4 types of assessment of environmental exposure (questionnaires, occupational history, expert assessment, direct exposure measurements);
  • Interpret a confidence interval for a rate ratio and for a difference in rates;
  • Calculate a population attributable risk;
  • Evaluate sources of bias, types of misclassification;
  • Identify a confounded variable;
  • Recognize effect modification.