Thread by @JeremyWilmer

Our new paper shows how 1 in 5 people categorically misinterpret bar graphs. A thread...

Press release: wellesley.edu/news/journalis…

Paper: jov.arvojournals.org/article.aspx?a…

#DataViz #DataJournalism #BarBarGraphs

When shown a bar graph that depicts average values, 1 in 5 people think that the bar's tip is the outer limit of the data, rather than the balanced center point (the average), as if every individual value was below-average. We call this error the "Bar-Tip Limit Error."

How could decades of graph interpretation research have missed such a severe error? Our experience in psychological measurement led us to ask a more concrete, direct, detailed question than prior work.

We developed a powerful new drawing-based measure of graph interpretation called Draw Datapoints on Graphs (DDoG). DDoG reveals correct and incorrect graph interpretation with unprecedented ease, building upon a rich tradition of drawing-based measurement in psychology.

As we write in the press release: "A major lesson from this work is that simplification in graph design can yield more confusion than clarification."

This work builds on the excellent research, teaching, tool-building, and communication of folks like @Birdbassador, @MattRKay, @JessicaHullman, @T_Weissgerber, @TheNewStats, @EdwardTufte, @EstimationStats, @MicahGAllen, @UpshotNYT, @NateSilver538 (and many others).

Broad take-home from our and their work: plots of summary statistics alone may yield frequent confusion and misinterpretation; the alternative of rich graphs that include individual-level data can be easy to make, easy to understand, engaging, and beautiful. #ShowTheData

An increasing number of great tools exist to easily create graphs that #ShowTheData. For example, our lab provides free, copy-paste-from-spreadsheet web apps at ShowMyData.org (built with #RStats and #RShiny).

Please spread the word: #ShowTheData
Our paper is "Two graphs walk into a bar: Readout-based measurement reveals the Bar-Tip Limit error, a common, categorical misinterpretation of mean bar graphs," by @SarahHKerns & @JeremyWilmer
jov.arvojournals.org/article.aspx?a…

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