Paul Krugman recently had a column asking why Republicans claim that they will deliver faster economic growth, even though growth has actually been considerably faster under Democratic presidents since at least the 1940s. His answer is that it's partly "epistemic closure: modern conservatives generally live in a bubble into which inconvenient facts can’t penetrate" and partly that they "need to promise economic miracles as a way to sell policies that overwhelmingly favor the donor class." It seems to me that he's trying too hard to make a mystery out of this. I think Republicans promise faster growth because they believe they can deliver it, and they believe they can deliver it because they have a "common sense" argument that they can: there are tradeoffs between different goals, and if you insist on things like equality or environmental protection, you'll pay a price in economic growth. And in my experience, most people (probably all people most of the time) base their opinions on what seems like common sense to them rather than on careful analysis of the available data.
However, his column led me to wonder if the "donor class" actually does better under the Republicans, or if a rising tide lifts all boats, so that all income groups do better under the Democrats. I obtained data from the World Top Incomes Database on the average income (adjusted for price levels) of the bottom 90%, the 90-5 percent, the 95-99 per cent, and the top one percent. Then I did a regression with percent change over the previous year as the dependent variable and party of the president as the independent variable. The classification of years when party control changes is difficult: the president is inaugurated in January, so the new party is in control for the great majority of the year, but the American economy is big and there's a lot of inertia. So I counted those years as half one party and half the other.
The average annual change in real income under the two parties:
0-90% 1.8% 0.0%
91-95% 2.0% 1.1%
95-99% 2.0% 1.2%
99-100% 2.0% 2.0%
The numbers in the World Top Incomes Database are pre-tax incomes, so it's likely that the top 1% really has done better under Republican presidents in terms of after-tax income.