Sensitivity Training for Building Better Bar Charts with SAS/GRAPH® Software
Perry Watts · 2008
This workshop combines instructions for chart building with principles defined by the statistical graphics experts, Edward Tufte and William Cleveland. Step-by-step instructions are provided for building midpoint, group and subgroup charts that use the graphics principles to generate publication-quality output. Gratitude is extended to SAS Institute Inc. for granting permission to use the DEPT data set from The How-To Book for SAS/GRAPH® Software by Thomas Miron [4]. Besides learning the GCHART procedure, time is spent on looking at how the PATTERN, AXIS, FORMAT and LEGEND statements are incorporated into chart building. Instructions are also provided in the workshop for creating a high-resolution graphics file and showing how it is transferred to PowerPoint for display. Even if you have minimal experience with SAS/GRAPH software, you should come away from this presentation knowing how to create a polished bar chart with GCHART. THE BAR CHART AS A GRAPHIC CONSTRUCT Definition: From Wikipedia: A bar chart, also known as a bar graph, is a chart with rectangular bars of lengths usually proportional to the magnitudes or frequencies of they represent. Bar charts are used for comparing two or more values. The bars can be horizontally or vertically oriented [6] (italics added). Missing from the definition is a description of the what that is being represented. For the bar chart that what is discrete nominal or ordinal data. Histograms are better suited for displaying ranges of continuous data. It can also be deduced from the Wikipedia definition that information in a bar chart is conveyed solely by bar length. As Figure 1 demonstrates, bar widths can be changed without altering the graph's message. History: Possibly the first bar charts appeared in the Commercial and Political Atlas (London, 1786) by William Playfair [6]. Displayed in Figure 2 is a hazy reproduction of Playfair's chart entitled CHART, Shewing at One View The Price of The Quarter of Wheat, & Wages of Labour by the Week --from-The Year 1565 to 1824. A more readable version of this graph appears in The Visual Display of Quantitative Information by Edward Tufte [5, p. 34]. Figure 1. Two bar charts convey exactly the same information, because the width of the bars has no intrinsic meaning. Count of Meetings by Department (Default Width Bars)