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Epidemiology Resource Center Home > Surveillance and Investigation > Surveillance and Investigation Division > Newsletters > Indiana Epidemiology Archived Newsletters > Easy Epidemiology E3 Easy Epidemiology for Everyone

Indiana Epidemiology Newsletter
January 2008

 E3is a new feature of the Indiana Epidemiology Newsletter dedicated to exploring the fundamentals of epidemiology  Each month, a different epidemiology concept will be explored to enhance understanding of basic epidemiology.

Descriptive Epidemiology

Epidemiologic method and surveillance were described in recent issues of the Indiana Epidemiology Newsletter. The epidemiologic method is the process of analyzing data patterns and interpreting those patterns. Surveillance is the process of collecting data and disseminating findings based on the data. Descriptive epidemiology is the first step in interpreting data patterns.

Descriptive epidemiology is the method of orienting the data collected and making the data useful. Answering the questions of who, what, where, when, and why are all aspects of descriptive epidemiology. Answering these questions standardizes the data to make sense and allows for patterns to emerge. Epidemiologists often organize data collected from surveillance according to person, place, and time to begin answering those questions.

One of the simplest methods of organizing the data is a line list. A line list may look like this:

Person Exposure Date Eaten Date ill Symptoms
Pammy ABC Restaurant 01/02/08 01/03/08 NVD
Tommy ABC Restaurant 01/04/08 01/05/08 NVD
Mikey ABC Restaurant 01/02/08 01/03/08 NVD
Jean ABC Restaurant 01/06/08 01/06/08 NVD

This line list indicates that people who ate at the ABC Restaurant between January 3 and January 6 developed nausea, vomiting, and diarrhea, typically within 24 hours of eating food at the restaurant. The line list facilitates interpreting preliminary information regarding time, place, person, and predominant symptoms.

Another method of organizing data is the epidemic curve.

Graph depicting the epidemic curve as explained below.

The epidemic curve is a simple way to describe an outbreak of disease. The x-axis (bottom) shows a measure of time, e.g., hours, days, or months. The y-axis (vertical) shows the count of cases for that measure of time.

Descriptive epidemiology really serves several purposes. First, it provides a systematic method for categorizing information about a public health event. Second, it helps identify the population at risk from the event being investigated. Third, it can provide quick information for investigators, decision-makers, media, and the public about the investigation and some possible causes of illness. Fourth, it gives the investigator the ability to quickly test hypotheses about the cause of the problem and can provide validation of the factors that lead to illness.

Descriptive epidemiology is the foundation on which the rest of the data analysis will take place. Until data are organized, more complex analysis is very difficult. More importantly, it provides a quick and simple picture for investigators and other partners in the investigation, especially those who have limited epidemiologic knowledge.

Next Month: Methods of Investigation.

Reference: Fontaine, R. Goodman, R. (2002) Describing the Findings. Field Epidemiology, Ed. Gregg, M. Oxford University Press, New York.