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How to Avoid Some Common Graphical Mistakes London October 1, 2012 Copyright © 2012, Naomi B. Robbins

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Graphical Mistakes Misleading the audience Not making the data stand out Problems with tick marks and labels Two useful graphical methods

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Graphical Mistakes Misleading the audience Not making the data stand out Problems with tick marks and labels Two useful graphical methods

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Avoid misleading the audience Equally spaced tick marks for unequal intervals Bar graphs with no zero Comparisons with different scales Figures not to scale

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Evenly spaced tick marks for uneven intervals

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Justice Dep’t version

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Comparison

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Another example

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Uneven ticks for same intervals

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Actuarial: Time handled correctly

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Bar charts with no zero Source:http://www.washingtonpost.com/blogs/ezra-klein/wp/2012/09/06/bill-clintons-speech-in-graphs/

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Novelty before accuracy

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Graphical Mistakes Misleading the audience Not making the data stand out Problems with tick marks and labels Two useful graphical methods

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Make the data stand out Factors that keep data from standing out: Clutter –Too many percent signs –Too many trailing zeros –Unnecessary dimensions Lack of contrast for model or data Graphical elements hide data

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USA Today – 4 October 2006

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Too many percent signs

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Percent Signs Removed

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Before and after

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Too many zeros

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Eliminate unnecessary dimensions

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Excel: 3-D bar chart

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Same data in two dimensions

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Not making the data (or model) stand out

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Colors interchanged

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Before and after

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Data and axis labels conflict

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Visual clarity not preserved under reproduction Most slides were yellow on navy so the handouts had the colors inverted. The figure on the right had a white background on the screen.

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Graphical Mistakes Misleading the audience Not making the data stand out Problems with tick marks and labels Two useful graphical methods

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Problems with tick marks and labels Too many labels Tick marks not at sensible numbers Labels hidden by grid lines or axes Labels not proofread

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Too many labels

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Another too many labels

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Tick marks at unreasonable values

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Reasonable values depend on variable

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Labels hidden

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Graph not proofread

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Graphical Mistakes Misleading the audience Not making the data stand out Problems with tick marks and labels Two useful graphical methods

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Useful graphical methods Dot plots Trellis graphics

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Bar plot of revenues

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Bar and dot plots of revenues

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Dot plot of profits

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Dot plot of profits and superposed plots

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Before: Multiple pie charts Source: Visualization by Brown et al.

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Before: Divided bar chart

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After: Trellis display

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Comparison

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For more information: Robbins, Naomi B. Creating More Effective Graphs blogs.forbes.com/naomirobbins

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