Unions, Education, and Simpson's Paradox

I know, I know, I never blog anymore. I hope to change that soon. Maybe.

But in the meantime, I had to draw attention to this post by IowaHawk. As Tyler Cowen observes, the post is marred by some unnecessary partisan vitriol. But the central point is nevertheless fascinating. Although unionized Wisconsin outperforms un-unionized Texas in educational performance when you look at overall figures, it turns out that Texas outperforms Wisconsin for every major ethnic group. Now, this might sound impossible, until you realize that Texas has a substantially higher percentage of blacks and Hispanics, who tend to get lower test scores regardless of the state.

I'm not trying to make political hay out of this; I'll leave that to others. No, the reason I find this so interesting is that, as a math nerd, I'm excited at any sighting of Simpson's Paradox in the wild. The same phenomenon can happen when, for instance, a hospital with better doctors gets a disproportionate number of the sickest patients. See here for a previous, albeit artificially constructed, appearance of Simpson's Paradox on this blog.