# Lesson 4: Displaying Public Health Data

This is an online version of a printed textbook. It is not intended to be an online course.

Refer to the book or to the electronic PDF version (511 pages) for printable versions of text, figures, and tables.

## Overview

Imagine that you work in a county or state health department. The department must prepare an annual summary of the individual surveillance reports and other public health data from the year that just ended. This summary needs to display trends and patterns in a concise and understandable manner. You have been selected to prepare this annual summary. What tools might you use to organize and display the data?

Most annual reports use a combination of tables, graphs, and charts to summarize and display data clearly and effectively. Tables and graphs can be used to summarize a few dozen records or a few million. They are used every day by epidemiologists to summarize and better understand the data they or others have collected. They can demonstrate distributions, trends, and relationships in the data that are not apparent from looking at individual records. Thus, tables and graphs are critical tools for descriptive and analytic epidemiology. In addition, remembering the adage that a picture is worth a thousand words, you can use tables and graphs to communicate epidemiologic findings to others efficiently and effectively. This lesson covers tabular and graphic techniques for data display; interpretation was covered in Lessons 2 and 3.

## Objectives

After studying this lesson and answering the questions in the exercises, you will be able to:

- Prepare and interpret one, two, or three variable tables and composite tables (including creating class intervals)
- Prepare and interpret arithmetic-scale line graphs, semilogarithmic-scale line graphs, histograms, frequency polygons, bar charts, pie charts, maps, and area maps
- State the value and proper use of population pyramids, cumulative frequency graphs, survival curves, scatter diagrams, box plots, dot plots, forest plots, and tree plots
- Identify when to use each type of table and graph