November 21, 2018C296013-H
Evaluation Briefs
Using Graphs and Charts to Illustrate
Quantitative Data
No. 12 | updated August 2018
Using visual representations to present data from Indicators for School Health, (SLIMS), surveys, or other evaluation
activities makes them easier to understand. Bar graphs, pie charts, line graphs, and histograms are an excellent way to
illustrate your program results. This brief includes concepts and definitions, types of graphs and charts, and guidelines
for formatting.
Major Concepts and Definitions
Graphs and charts condense large amounts of
information into easy-to-understand formats that
clearly and effectively communicate important points.
In selecting how best to present your data, think about
the purpose of your graph or chart and what you want
to present, then decide which variables you want to
include and whether they should be expressed as
frequencies, percentages, or categories.
When you decide what kind of graph or chart best
illustrates your data, you should consider what type
of data you are working with. Categorical data are
grouped into non-overlapping categories (such as
grade, race, and yes or no responses). Bar graphs,
line graphs, and pie charts are useful for displaying
categorical data. Continuous data are measured on
a scale or continuum (such as weight or test scores).
Histograms are useful for displaying continuous data.
Bar graphs, line graphs, and histograms have an x- and
y-axis. The x-axis is the horizontal part of the graph and
the y-axis is the vertical part.
Types of Graphs and Charts
• A bar graph is composed of discrete bars that
represent different categories of data. The length or
height of the bar is equal to the quantity within that
category of data. Bar graphs are best used to
compare values across categories.
• A pie chart is a circular chart used to compare parts
of the whole. It is divided into sectors that are equal in
size to the quantity represented.
