Turn the tables

Today’s note is about the very worst sort of graph: a table. Of course, a table is not a graph, but that is the point: it almost always should be. Here is a table that appeared recently to make a very simple and powerful point. To further my argument, however, I won’t tell you what that point is, and ask you to deduce it from the table. I will time you. ready? Go!

Ok. Stop! Time’s up. Did you get the point? I thought not.

Now here are the same data as a graph. Now do you get the point? The graph shows changes in the Gross Federal Deficit, as a percent of Gross Domestic Product, for the last nine presidential administrations. Above the zero line are increases in the deficit (bad). Most of the colored areas above the line (bad) are red (republican) and most of those below the line (good) are blue (democrat). So much for the notion of “tax and spend” democrats and “fiscally responsible” republicans!

But of course this column is scrupulously fair and balanced, so our point here is not the political one, but the graphical one.

The main lesson here is a very elementary one. Never use a table when a graph is possible. Graphs by their nature render data into visible patterns that jump out at the reader. Tables have a purpose – to provide access to numerical values – but they rarely make anything self evident, and they rarely show trends without scrutiny, thought, and calculation.

It may be worth mentioning some of the design decisions that went into my graph.

First, note that there is no horizontal axis. We leave out the dates because they add little to the story. The rectangles are the correct width (4 or eight years), and are in the correct order. adding dates would just be clutter.

Second, we used a rectangle graph, in which the width of each rectangle represents the length of each presidential term. And the vertical axis is deficit change per year. So the area of each rectangle represents the total change during each administration. This is appropriate, since the visual impact is proportional to area, and the total deficit from each administration is the key quantity we wish to convey.

We add the names of the Presidents, since that is of some interest, but put them in light gray, since their identities are not central to the point being made.

We add a small key, to remind readers of the meaning of the two colors. While these colors have become conventional for the two parties, we can’t assume the key will be obvious.

We leave out any extraneous lines, text, shading, or decoration. Just the facts, ma’am.

Reference:  The Atlantic, January 2, 2011.



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