The downside of discouraging pie charts

It's no secret most dataviz experts do not like pie charts.

Our disdain for pie charts causes people to look for alternatives.

Sometimes, the alternative is worse. Witness:

This chart comes from the Spring 2018 issue of On Investing, the magazine for Charles Schwab customers.

It's not a pie chart.

I'm forced to say the pie chart is preferred.

The original chart fails the self-sufficiency test. Here is the 2007 chart with the data removed.

It's very hard to figure out how large are those pieces, so any reader trying to understand this chart will resort to reading the data, which means the visual representation does no work!

Or, you can use a dot plot.

This version emphasizes the change over time.

 

Comments

[derek]

For a line chart showing change over time, I think I might prefer a time series like this.

I notice that by coincidence the sum of Treasuries and Securities is unchanged between 2007 and 2017, so if they'd gone for a four panel Marimekko like this. Then you can see the changes in area as changes in rectangle length.

[jlbriggs]

I mean...yeah, the pie charts are better.
But the pie charts are still a pretty bad way to compare this data. I wouldn't call it a downside to discouraging pie charts, but a downside to a general lack of understanding effective data visualization! :)

Hard to imagine the thought process behind building that. Hard to imagine what tool made it seem like a good option, or how a tool would even go about laying the data out that way. ¯\_(ツ)_/¯

The three ways I would look at visualizing this data are:

- Slope Graph
- Bar Chart with line for comparison year (like a simplified bullet chart)
- Dot Plot (as you've done)

If the goal is seeing the change directly, the slope would be my preference.
If the goal is seeing the current values, with the previous values as context, the bar with comparison like would be.
I think both do a somewhat better job than the dot plot, for those two respective purposes.