EVALUATING COMPUTER GRAPHING PROGRAMS By Norman Higgins

E veryone recognizes the value of well designed graphs for presenting numeri- cal information. Graphs are widely

, used in school classrooms and in busi- ness boardrooms to display quantitative

information for learning and for decision-making. In recent years several computer application pro- grams have been developed that will create graphs for projection as 35mm slides or as overhead transparencies. How well do the graphs created with these computer graphing programs measure up to commonly accepted standards for the design of statistical graphs and for the design of projected audiovisual materials? Evaluation standards for projected graphical displays and their use in evalu- ating graphs created with computer graphing pro- grams are described in this article.

What standards are used to assess the quality o f projected graph materials? Two widely recog- nized sources of standards for the design of graphs are The Visual Display of Quantitative Information by Edward Tufte (1983) and Statistical Graphics Design Principles and Practices by Calvin Schmid (1983). A standard reference for the design of pro- jected materials is Legibility-Artwork to Screen published by Eastman Kodak (1983). A list of standards for assessing the quality of line graphs and bar graphs compiled from these three sources is presented in Table 1. The standards listed in- clude a rich mixture of graphing principles, typo- graphic considerations, and esthetic preferences.

Table 1. Design Standards for Projected Graphs

Accuracy. Numerical data is presented accurate- ly and without distortion.

Labeling, Textual information has a left to right orientation. Words are spelled out, not abbreviat- ed. Scales and data lines or bars are contiguously labeled, no legend is needed. Units of measure are included in the title or in the scale labels. Labels are centered on grid lines and on graph bars. Type used for labels is bold, upper-lower case, and at least 1/25th the height of the display field (18 point type size on 6' • 9' artwork for 35mm slides).

Norman Higgins is a professor in the Educational Media and Computers Department, College of Education, Arizona State University at Tempe.

Design standards provide a useful checklist for selecting computer graphing programs and for improving the quality of the graphs produced by them.

Grid Lines. A minimum number of grid lines for accurate reading are included. Grid lines are lighter in weight than zero scale lines.

Scales. The intervals on a particular scale are equal in length. The intervals used for the vertical and horizontal scales produce a graph with a 2:3 height to width ratio.

Graph Lines and Bars. Graph lines are distinctly different from one another and are heavier in weight than zero scale lines. Bars are uniform in width, not too wide or too narrow, and are not ex- cessively long. The space between bars or be- tween bar clusters is 1/5 to 1/2 the width of indi- vidual bars. Simple shading or distinctive colors are used to differentiate the bars.

What set o f numbers is used to create the graphs that are evaluated? The set of numbers used to create the graphs that are to be evaluated should be representative of the numerical data that are likely to be encountered in everyday life. The set should be representative with respect to the number of variables to be graphed, the range of numerical values for each variable and any ano- molies that are likely to be encountered in the data. The set of numbers presented in Table 2 has four variables to be plotted: the time period, the number of home weavers, the number of factory weavers and the amount of cloth produced. It in- cludes three units of measure: years, weavers, and pounds. It includes a wide range of values that ex- tend from zero home weavers working in 1880 to one billion pounds of cloth produced in the same year. The values are expressed as X1 Thousand and X2 Million to reduce the excessive difference between the number of weavers and the pounds of cloth. The time periods are reported in unequal in- tervals of 10, 15, and 20 years.

The evaluation reported in this article was sup- ported in part by a grant from the College of Edu- cation Faculty Research Incentive Program, Ari- zona State University.

MA~JUNE 13

Table 2. Home and Factory Weaving Production England 1820-1880

Year Home Factory Pounds Weavers Weavers Cloth

X1 Thousand X1 Thousand XIMillion

1820 240 I0 37.5 1830 230 50 75 1845 60 150 175 1860 10 200 325 1880 - - 250 500

How good are the graphs created from comput- er graphing programs? Three types of graphs can be created from the numerical information pre- sented in Table 2: a multiple line graph, a multiple bar graph, and a combination bar and line graph. The three types of graphs are presented in Figures 1, 2, and 3. The three graphs were created with the Cricket Graph (Version 1.2) program using the preset program default settings. The standards list- ed in Table 1 can be used to assess the quality of each graph.

The line graph in Figure I displays the weaving production information accurately and without dis- tortion. Although the data points are not labeled on the time scale they are properly spaced to match the unequal time intervals used in the set of numbers graphed. The text in the title and legend is oriented left to right with words spelled out in upper and lower case type. The type size is appro- priate, but the style is not bold. Graph line labels are not placed on the graph next to their referents, but are located outside the graph in a legend. The units of measure are not listed in the title or in footnotes. There are no vertical or horizontal grid lines to facilitate reading the graph line values. The scales do have equal intervals numbered in in-

crements that are multiples of five. The scale in- tervals are sized to produce a esthetically pleasing 2:3 height to width ratio. The vertical scale label is inaccurate, is abbreviated, and does not read from fight to left. The graph lines are not distinctly dif- ferent from one another and are not much heavier in weight than the zero scale lines on the bottom and left side of the graph. Although the line graph meets several of the standards for good graphs, it fails to meet several standards that would make it an easier graph to read.

Application of the design standards to the multi- ple bar graph presented in Figure 2 reveals the same characteristics as the line graph with respect to accuracy, labeling, grid lines and scales. The bar shading though distinctly different is not sim- ply patterned and does not easily differentiate be- tween the two groups of weavers or between the groups of weavers and the amount of cloth pro- duced. There is adequate space between the bar clusters. As with the line graph, the bar graph meets some but not all of the standards for good graphs. It too can be improved for readability.

Application of the design standards to the com- bination bar-line graph presented in Figure 3 re- veals many of the same characteristics as the line and bar graphs previously analyzed with several noticeable differences. The graph line that indi- cates cloth production is easily differentiated from the bars the indicate the number of home and fac- tory weavers. The bar clusters are easily distin- guished because there are spaces between them. There is some distortion in the cloth production graph line. The distortion results from the equal spacing of the unequal time intervals on the hori- zontal time scale.

Although the combination bar-line graph is an improvement on the line and bar graphs it can still be improved as application of the design standards suggests.

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HOME AND FACTORY WEAVING PRODUCTION ENGLAND 1820 - 1880

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100

0 1800 1820 1840 1860 1880

Y E A R S

1900

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Figure 1. Unedited Multiple Line Graph

HOME WVRS

FACT WVRS

CLOTH PROE

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HOME AND FACTORY WEAVING PRODUCTION ENGLAND 1820 -1880

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500

400

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1820 1830 1845 1860 YEARS

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Figure 2. Unedited Bar Graph

HOME AND FACTORY WEAVING PRODUCTION ENGLAND 1820 -1880

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Figure 3. Unedited Bar-Line Combination Graph MAY/JUNE 15

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Home and Factory Weaving Production England 1820-1880

500

400

300

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100

H o m e -Weave X l 0 0 0

1 8 2 0 1 8 3 0 1 8 4 5

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Figure 4. Edited Weaving Production Graph

A fourth graph was created using the editing features of the Cricket Graph program. This edit- ed combination bar-line graph, designed to correct the faults of the previous graphs, is presented in Figure 4. The editing in this graph consists of the selection of a bold type style for the text and the selection of more simple and distinctive patterns for the bars. The legend and scale labels were de- leted. Labels were placed on the graph next to the bars and the graph line that they reference. Hori- zontal grid lines were added and the graph was re- sized for better legibility.

Are the design standards and number set useful for evaluating graphing programs? The design standards and the set of numbers used to create the graphs presented in Figures 1 through 4 are capable of exposing a wide range of faults in com- puter generated graphs. They can be used to ex- pose faults that may not be directly related to computer program features--these are designer faults such as not including units of measure in a title or in scale labels. They can expose faults that result from using inappropriate preset program de- fault settings such as illegible type sizes or styles, indistinguishable graph lines or bars, and too few or too many grid lines. Once identified, design faults that result from program default settings may be corrected by either changing the settings or by judicious use of the program editing fea- tures.

Design standards provide a useful checklist for selecting computer graphing programs and for im-

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proving the quality of the graphs produced by them. Without design standards, computer graph- ing programs become one more source of visible pollution in the environment. Children in class- rooms and business men in boardrooms will be ex- posed to a haze of illegible labels, indistinguish- able graph lines, confusing legends and annoying bar patterns in order to read the information pre- sented in graphical displays. Media designers who know graphical design standards and who know how to use them to improve computer generated graphs are a front line of defense in the fight against visible pollution in the learning envir- onment. �9

REFERENCES

Cricket Software. (1985). Cricket graph: Presenta- tion graphics for science and business [Comput- er program]. Philadelphia, PA: Cricket Soft- ware.

Eastman Kodak Company. (1983). Legibility- artwork to screen (Kodak Pamphlet S-24). Rochester, NY: Eastman Kodak Company

Schmid, C. (1983). Statistical graphics: Design principles and practices. New York, NY: John Wiley and Sons.

Tufte, E. (1983). The statistical display of quanti- tative information. Cheshire, CN: Graphics Press.