Ring-around-the-rosy

In my last post, I railed against the feeble graphics of a recent report on salaries in the life sciences.  In the same report, we find the following “infographic.”

Since there is no additional information, we are left on our own to deduce its meaning. It seems to be saying something about average salaries in various sectors of the economy: academic, government etc.

But why are the data arranged on a ring? Are we meant to perceive the fraction each sector takes of the total salary pie? No, because no information is given about the numbers of employees in each sector. If we are meant just to compare the numbers, displaying them as fractions of a ring is a remarkably bad way to do it. Quick: which sector has the largest salaries? I bet you cheated and looked at the numbers.

And what are those little people doing wandering around in the center of the ring? Are they matadors in the bullring? Christians in the Colosseum? Oh, I see. After getting out my magnifying glass I see that some of them are wearing skirts. Or have their pockets inside out? Evidently the numbers are being split by gender. Again, since the wedges are poor at conveying magnitude, the designer has helpfully provided numerical labels, for each gender, in what appears to be 4 point type. With the magnifying glass, the numbers can be read.

OK, Mr. Smarty-pants, how would you do it? Well how about the completely obvious solution of plotting the salaries on the vertical axis, connecting and color coding  data for each gender, and sorting by male salary. We assume that the big printed numbers on the ring are the mean, and we plot that too. We print the sectors in a light gray below the data, rather than have a separate key, which obliges you to look back and forth and back and forth and…well, you get the idea.

 

We also show the zero value on the vertical scale. This is called a “ratio scale”, but technical buzzwords aside,  the concept is very simple: you can compare the size of the differences to the size of the total salary. We also add very faint horizontal gridlines. This allows you to read off numbers if you wish, but does not clutter up the main contour lines.

I hope you will agree that my plot gets right to the point: it immediately and effortlessly shows the way in which salary varies with sector, and shows the disparity between men and women. Those are the key goals of a graph: effortlessness, and immediacy.

Reference:

Life Sciences Salary Survey, 2010

http://www.the-scientist.com/fragments/salary_survey/2010/ss-charts2010.jsp

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