Wednesday, August 27, 2014

To make visualizations that are truthful and persuasive, show all relevant data

Today, the NYT's The Upshot published a very nice line chart showing projections of Medicare spending per recipient. This one:

My reaction when I saw it was to ask for another chart with total projected spending (I wasn't the only one.) It's likely that the U.S. will have a larger number of retirees in the future than it does now, and arithmetic is a bitch: ‘Spending per recipient’ times ‘number of recipients’ can kill the best optimistic story.

Here's why I wanted that second chart: If you're a diehard fan of The New York Times, like me, you'll be inclined to buy this argument. You'll trust David Leonhardt Margot Sanger-Katz when he she writes that projections reveal a positive trend, no matter the way you look at the data. But what about if I were a regular reader of The Weekly Standard (just to mention one high-brow conservative publication)? I wouldn't be persuaded by these NYT egghead liberals*. I believe that I'd need to see all the relevant data, both the spending per recipient and the total spending, to be convinced.

I thought that this could be a great example for class, so I began looking for the data. I visited the CBO report mentioned in the story, and found the one from last year. Here's a screenshot of the most recent projection of total Medicare spending in the next ten years:

I was planning to design the second line chart myself but, fortunately, Kevin Quealy, author of the original graphic, had already done it. See it below. Numbers are in millions of dollars.

I'll stick to my guns in this case: Both charts are equally relevant to the story. I'd publish them next to each other. The future certainly looks brighter than a year ago, but not as bright as the first chart may lead us to think. Alex Walsh made an additional interesting suggestion.

UPDATE: Sanger-Katz has just shared a link to a story explaining demographic trends.

*I don't know if Leonhardt Sanger-Katz and Quealy are liberals, of course, but The New York Times is generally considered a publication that sympathizes with liberal ideas.