Making major things easy, and minor things hard

A recent issue of Significance magazine carried the following stacked column chart showing how the driver license status of men and women change as they age. The data came from the U.K.

Quick question - what percentage of British men in their sixties hold full driver licenses?

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I was just kidding. Those questions can't be quickly answered on a stacked column chart. That's because you have to find the axis, and then mentally invert the axis.

On that chart, larger values are shown pointing down (green) and also pointing up (blue), and ... well, I don't have words for the yellow. In fact, the yellow segments, showing people without licenses, are possibly the most important category for this report.

In making decisions about visualizing data, it's important to separate out the major things from the minor things.

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Here is a reimagination of the chart using connected dots:

What is hard to do using this chart is to verify that the three proportions add to 100%. What is easy is to read off the proportion for any gender, age and license status subgroup.

It's really quite intricate how these researchers binned the age data. There are bins of size 1, 4, 5 and 10, plus the top group is 85 and above. The way I handled these is to turn everything to 1-year bins. I assume that in the wider bins, we don't have precise data for each age, and the bin value is the average among the bin, thus it is as if someone had drawn a horizontal line across the bin width. (I left the top bin alone as I don't know what is the maximum age of a person in this study.)

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Those of you who have laminated the flowchart of data visualization are probably irate. According to such a flowchart, one must use a column chart because the x variable (age band) has irregularly-sized discrete values, and one must use a stacked column chart because the y variable is a percentage, grouped by a third variable (license status).

Don't be mad, just ditch the flowchart.

 

Comments

[alex]

to be honest, i find the first chart tells the story better. you're right that it's more difficult to know the exact value for men in their sixties, but that's not really the point of the chart.