Accountability Modules WHAT IT IS Return to Table of Contents

Data Analysis: Displaying Data - Graphs
Graphs are pictorial representations of the relationships between two (or more) variables and are an important part of descriptive statistics. Different types of graphs can be used for illustration purposes depending on the type of variable (nominal, ordinal, or interval) and the issues of interest. This module discusses some of the more common types of graphs. Graphs can be used any time one wants to visually summarize the relationships between variables, especially if the data set is large or unmanageable. They are routinely used in reports to underscore a particular statement about a data set and to enhance readability. Graphs can appeal to visual memory in ways that mere tallies, tables, or frequency distributions cannot. However, if not used carefully, graphs can misrepresent relationships between variables or encourage inaccurate conclusions. (See the module on Deception with Graphs for more information.)

WHEN TO USE IT

TYPES OF GRAPHS Bar Graphs

Bar graphs are commonly used to show the number or proportion of nominal or ordinal data which possess a particular attribute. They depict the frequency of each category of data points as a bar rising vertically from the horizontal axis. Bar graphs most often represent the number of observations in a given category, such as the number of people in a sample falling into a given income or ethnic group. They can be used to show the proportion of such data points, but the pie chart is more commonly used for this purpose. Bar graphs are especially good for showing how nominal data change over time. Advantages - Bar graphs can: + show each nominal or ordinal category in a frequency distribution + display relative numbers or proportions of multiple categories + summarize a large data set in visual form + clarify