The following chart showed up on my Twitter feed last week. It's a cautionary tale for using software defaults.

Booksaleschart_sourceBISG_fromtwitter

 At first glance, the stacking of years in a bar chart makes little sense. This is particularly so when there appears not to be any interesting annual trend: the four segments seem to have roughly equal length almost everywhere.

This designer might be suffering from what I have called "loss aversion" (link). Loss aversion in data visualization is the fear of losing your data, which causes people to cling on to every little bit of data they have.

Several challenges of the chart come from the software defaults. The bars are ordered alphabetically, making it difficult to discern a trend. The horizontal axis labels are given in single dollars and units, and yet the intention of the designer is to use millions, as indicated in the chart titles.

The one horrifying feature of this chart is the 3D effect. The third dimension contains no information at all. In fact, it destroys information, as readers who use the vertical gridlines to estimate the lengths of the bars will be sadly misled. As shown below, readers must draw imaginary lines to figure out the horizontal values.

Twitter_booksalescategories_0

The Question of this chart is the distribution of book sales (revenues and units) across different genres. When the designer chose to stack the bars (i.e. sum the yearly data), he or she has decided that the details of specific years are not as important as the total - this is the right conclusion since the bar segments have similar measurement within each genre.

So let's pursue the revolution of averaging the data, plotting average yearly sales.

Redo_twitter_bookssalescategories

This chart shows that there are two major types of genres. In the education world, the unit prices of (text)books are very high while sales are relatively small by units but in aggregate, the dollar revenues are high. In the "adult" world, whether it's fiction or non-fiction, the unit price is low while the number of units is high, which results in similar total dollar revenues as the education genres.

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Simple lesson here: learn to hate software defaults

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junkcharts
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