Razing the bar

Like most folks, I am convinced that my prejudices are grounded in logic and common sense. But in my case, they really are. Really.

For example, I have an outsized contempt for the bar graph. In my view, it almost always makes relationships difficult to discern, and masks what information is present with massive amounts of obscuring ink. I will have more contemptuous things to say about the bar graph in the future, but for now, lets consider an example.

Here is a chart that appeared recently in the New York Times (Rethinking Early Retirement in Europe, Oct 29, 2010). The context is an otherwise worthy article by Floyd Norris on early retirement in various countries. The chart shows, for men and women separately, the proportion in each age group who are working or seeking employment.

Now most of you will struggle to make out anything here, because everything is too small. And that’s because the artist was dealing with a lot of data. Well, actually, no. The amount of data here is rather modest. It is only the amount of space used that is extravagant.

And what point do you get when you first “grok” the picture? At best, with a moment’s study, you might appreciate that people work less as they get older. But that is hardly the point of the story. Rather that point is that the French retire early. Does that jump out at you from the figure? I didn’t think so.

Now lets see if we can do better. Here is my quick version. I have plotted the data as a line graph, and the data for each country form a line, coded by color. This immediately shows the rate of decline for each country, and quickly shows how France stands out from the rest.

Of course, if the point of the story is only that the french retire early, then why not show that instead? In my next graph I have shown the french male labor force participation, as a fraction of average participation across the other five countries. Here the point is even more obvious. It jumps out at you. That is what should happen with a good graph.

In my first graph I showed shown men and women separately, as in Mr. Norris’s graphic, but here again, what is the point being made? If it is the relative participation in he workforce of men and women, and how that changes over time, then show that! In my next figure I show the ratio of men and women, for each country, over time. This makes it easy to see, for example, that in all countries men outnumber women in the workplace, and that the imbalance increases with age. It also makes it easy to see the relatively high participation of US women, over all age groups.

So, what are the lessons? First, avoid the bar graph. Second, use lines to connect related quantities and show trends. Third,allow the reader to easily make comparisons, where that is intended. Fourth, use a graph that makes your point. Don’t force the reader to do their own analysis. Otherwise, you might as well provide (horrors!) a table of numbers.

Reference:

Rethinking Early Retirement in Europe, New York Times, Oct 29, 2010.

http://www.nytimes.com/2010/10/30/business/30charts.html

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