After my last graph analysis, a reader asked that I review the following graph from a New York Times columnist’s blog post on income disparity.
Overall, I think this graph is good. Everything is labeled, making the message clear, but there are several minor problems with the details.
- The rotated year labels are hard to read, especially since they’re not on even multiples of 5s or 10s.
- The data points and connecting lines are fighting for attention and saying the same thing. Either de-emphasize/remove the points or replace the connected lines with a smoother.
- The grid lines are too bold — competing with the data marks.
- The labels use inconsistent capitalization (and there appears to be a missing space in “classAmerica”). It’d be nice if all the labels were within the graph frame, too.
I don’t know enough about economics to comment on the currency of the graph’s message. One commenter suggested that the exclusion of capital gains diminishes the value of the data. I found the original paper [pdf], and the absence of capital gains seems to stem from the way the data was collected from income tax records though it is justified by calling capital gains “lumpy” and “volatile” and so presumably independent of long-term trends.
Here are a couple of attempts I made a reproducing the graph to fix the minor problems. I used GraphClick (great product) to get the data. (The original paper’s data only goes through 1998.)
My first graph leaves off the labels, uses fainter data points and gridlines and adds a spline smoother to show trends. Labels can be added in a variety of ways to highlight sections of interest.
In my second graph I experiment with labeling ranges more specifically than with just a single arrow. With an arrow, it’s unclear whether it’s pointing to a single event or a section. The shading fixes that problem but adds other distractions that probably aren’t worth the price.