Under Democratic administrations since 1960, RGDP grew at a little more than 4% a year. Under Republican administrations, a little less than 3% a year. That means that the during the average Republican adminsitration the economy had 6% less growth over the four-year term than if the economy were performing at the average Democratic rate. That means we would have about a 44% better economy in real terms if the economy would have grown at the average Democratic rate.
Would a Democratic victory in those presidential elections have produced that? That's a complicated question that I consider after the jump.
The first thing to know is that I'm dealing with the time since 1960 because that's the figures which are readily available. The Economic Report of the President is available on line, and it reports real gross domestic product bact to 1959 in table B2. (It's a government report, fronted by something signed by Bush, compiled by the staff of the Council of Economic Advisors.)
The figures I've seen for previous times deal with the real gross national product. That's not all that different, and the partisan comparison isn't all that different. The growth was slower under Eisenhower than it was under Truman's last term or the Kennedy and Johnson periods. (From '44 to '48, the figures for the total economy decreased, but the figures for everything else than the federal purchase of goods and services -- fighting WWII -- increased substantially. The growth from 1940 to 1948 was rapid.)
Would Democrats have produced a 44% larger economy had they been in the White House? Would it have been a smaller increase or a larger one.
The question is impossible to answer definitively.Increase in real GDP breaks down into an increase in population, a decrease in unemployment, and an increase in productivity.
The unemployment rate increases under Republican administrations and decreases (almost always) under Democratic administrations. But the decrease is clearly limited; it can't go below (or, realistically, very close to) zero. And it could not have continued at the typical Democratic rate for 24 more years. So one part of the Democratic advantage could not have occured.
On the other hand, the growth under Democratic administrations following other Democratic administrations is appreciably greater than the growth rate under Democratic administrations following Republican administrations. If there only had been the first sort, growth might have been even greater.