Using Graphs to Communicate

“A good graph is worth a thousand words.”  Dennis Johnston in Data Analysis for Continuous School Improvement.  Victoria L. Bernhardt, Ph.D.  Eye on Education, 2004.

“Appropriate graphs are simple – not complex – can stand alone, and are clear about the information they try to compare. The most common types of graphs used for displaying school-wide data are pie, bar, and line graphs.”

Pie Charts

• Use to stress proportions or percentages of a population or category; e.g., how a resource such as the general fund is apportioned for various uses or the percent of subgroups of students in the district’s total enrollment.
• Use no more than eight slices in any pie graph.
• Do not use red and green together (5% of the population cannot distinguish between red and green).
• Do not use patterns next to each other that result in optical illusions.

Bar Graphs

• Use for descriptive data such as frequencies, percentage and averages;   e.g., your district’s assessment results over time as displayed in the district report card and the stacked bar graphs (% proficient or above) that appear in the reports for the Achievement Tests.
• Use a title that tells specifically what the graph represents.
• Be sure to label both the horizontal and vertical axes.
• Make sure the colors contract enough to show the data clearly.

Line Graphs

• Use to show a series of numbers over time (trend data); e.g. a student or grade level reading achievement test scores for a number of years.
• Look for a least seven data points in a consistent direction before concluding that true change has occurred.

Graphs from 2005-2006 Annual Report on Educational Progress in Ohio. Ohio Department of Education, 2006.