From the column:

Since 1933, the economy has grown at an annual average rate of 4.6 percent under Democratic presidents and 2.4 percent under Republicans, according to a Times analysis. In more concrete terms: The average income of Americans would be more than double its current level if the economy had somehow grown at the Democratic rate for all of the past nine decades. If anything, that period (which is based on data availability) is too kind to Republicans, because it excludes the portion of the Great Depression that happened on Herbert Hoover’s watch.

The six presidents who have presided over the fastest job growth have all been Democrats, as you can see above. The four presidents who have presided over the slowest growth have all been Republicans.

The big question, of course, is why. And there are not easy answers.

I have shown the data to multiple economists in recent weeks, and most say they are not sure how to explain it, at least not fully. “We don’t quite get why it’s the case,” Katherine Eriksson, a professor at the University of California, Davis, who specializes in economic history, told me. Marianne Wanamaker, an economist at the University of Tennessee, described the pattern to the graduate students in a class she teaches and asked for their thoughts. “They were sort of stumped,” she said. ...

What, then, are the most plausible theories?

First, it’s worth rejecting a few unlikely possibilities. Congressional control is not the answer. The pattern holds regardless of which party is running Congress. Deficit spending also doesn’t explain the gap: It is not the case that Democrats juice the economy by spending money and then leave Republicans to clean up the mess. Over the last four decades, in fact, Republican presidents have run up larger deficits than Democrats.

That leaves one broad possibility with a good amount of supporting evidence: Democrats have been more willing to heed economic and historical lessons about what policies actually strengthen the economy, while Republicans have often clung to theories that they want to believe — like the supposedly magical power of tax cuts and deregulation. Democrats, in short, have been more pragmatic.