NAEP Reporting Practices Investigating District-Level and Market-Basket Reporting (2001) / Chapter Skim
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Appendix B: Depicting Changes in Reading Scores--An Example of a Usability Evaluation
Appendix B: Depicting Changes in Reading Scores--An Example of a Usability Evaluation
Pages 125-136
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From page 125... ...
. The format chosen is a perspective-view bar graph with region represented along the horizontal axis and grade represented in depth (z-axis)
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~ _: ILL:_ ,j, it, 992 1994 West ~:~:~:~:~:~:~:~ tarade 12 Grade 8 Grade 4 by the relevant display objects. He also included a legend to help readers identify individual lines.
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What kinds of conclusions would they like to be able to draw? By giving panelists the data sets in a number of formats (numerical data tables and existing graphs in the present case)
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These questions should drive decisions about the content and structure of data displays. In addition, when performing usability tests on the comprehensibility of the data display, users' abilities to answer these questions accurately should be a core criterion of design success.
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This also suggests that displaying the exact data values in conjunction with the graph, as in the original bar chart, may be unnecessary and may even impede rapid access of the comparative information. Our revised display, like the two previous versions, will be graphical.
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In terms of the relative salience of other graphic elements, the revised graph clearly highlights changes in scores from 1992 to 1994 that are different in magnitude or direction across the geographic regions. However, this salience may actually be misleading in making certain perceptual comparisons across grade levels.
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From page 131... ...
In addition to scores from the four regions, a fifth line represents mean scores across the entire United States. This would seem to be important data to represent directly, given our hypothetical users' need to know how students in the United States are performing across the two years.
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We should also be aware of the potential visual distortions or illusions that can occur in both the original and revised graphs. In the original graph, the use of linear perspective and other depth cues (e.g., occlusion)
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We will attempt to avoid the use of both perspective and line slope in our revision of the NAEP reading scores graph. Is the organization of information in the display compatible with spatial metaphors and population stereotypes' When the purpose is to show regional differences, the display should consider cartographic conventions of representing North at the top of a map and West to the far left.
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Within each grade level there are four lines, each representing the two mean scores for a region. Rather than connecting two points that are offset horizontally, the revised graph uses two points along the same vertical grid line to represent the two test administration dates.
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A diamond indicates that the average score remaind the same. Grade 12 300 280 Grade 8 270 265 255 250 Grade 4 220 2~0 West Midwest Southeast Northeast West Midwest Southeast Northeast West Midwest Southeast Northeast
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From page 136... ...
and Neilsen (19931. If the graph were to be included in the next release of NAEP reports, then data on citations, requests for publication, and misinterpretations by the press can also be collected to gauge display comprehensibility and accessibility.
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