Several problems with stacked bar charts, as demonstrated by a Delta chart designer

In the Trifecta Checkup (link), I like to see the Question and the Visual work well together. Sometimes, you have a nice message but you just pick the wrong Visual.

An example is the following stacked column chart, used in an investor presentation by Delta.

From what I can tell, the five types of aircraft are divided into RJ (regional jet) and others (perhaps, larger jets). With each of those types, there are two or three subtypes. The primary message here is the reduction in the RJ fleet and the expansion of Small/Medium/Large.

One problem with a stacked column chart with five types is that it takes too much effort to understand the trends of the middle types.

The two types on the edges are not immune to confusion either. As shown below, both the dark blue (Large) type and the dark red (50-seat RJ) type are associated with downward sloping lines except that the former type is growing rapidly while the latter is vanishing from the mix!

 In this case, the slopegraph (Bumps-type chart) can overcome some of the limitations.

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This example was used in my new dataviz workshop, launched in St. Louis yesterday. Thank you to the participants for making it a lively session!

Comments

[Shane Cone]

Thanks for the suggested alternative! I sat through an awful display of stacked bar charts recently. There are so many issues with them. One has to be so careful that the message is actually coming through when you look at the chart; as you show, it takes some work to figure out what it all means!

[Matthew Zadrozny]

Nice and informative site, but the ads detract from it (and its messagE) and the slogan "Recycling chartjunk as junk art. A blog by data visualization critic, Kaiser Fung." isn't visible.