The Grand Old Party (GOP) is known for supporting big business. So it pays to elect Republicans to the White House, right? If you analyze the stock market performance under Republican and Democratic presidents, the answer is a resounding NO. Democratic presidents generate average stock market returns in excess of the risk-free rate of 10.69% -- roughly six times the 1.69% earned under Republican administrations.

Investopedia describes the research of Pedro Santa-Clara and Rossen Valkanov who analyzed the value-weighted returns on stocks between 1927 and 1998 under Democratic and Republican presidents. And they found that the excess returns of stocks over the risk-free rate of return -- as measured by the Center for Research into Securities Prices (CRSP) indexes versus three-month Treasury bill rates -- were far higher for Democratic presidents (10.69%) than for Republican ones (1.69%).

Of course, these are just long-term statistics. Under the last Democratic president, stocks rose an annual average of 17.4%. The current Republican White House occupant has presided over an average annual decline of 1.1% -- the S&P 500 was 1,342 when he took over and stands at 1,233 today -- the only president of either party of the last 11 to oversee a decline in stocks.

The New York Times reports that a new book -- Unequal Democracy by Larry M. Bartels, a Princeton economics professor -- contains statistics that demonstrate an important historical pattern -- the U.S. economy does better under Democratic presidents than under Republican ones. That is, the last eight years -- in which the median income shrank while consumer prices rose -- is just an extreme example of the economic impact of Republican presidencies.

And based on statistics from Forbes, the stock market also does better under Democratic presidents. Forbes "found that the S&P 500 has averaged a total return of 14.1% per year under Democratic presidents since April 1945, and 11.8% under Republicans. The best total returns--17.4% per year--were under Bill Clinton, whose presidency ranked first in economic results."

How much better does the economy do under Democrats? The Times reports that between 1948 and 2007, Gross National Product (GNP) growth per capita was 1.14 percentage points higher under Democrats (2.78%) compared to 1.64% for Republicans. The Times reports "that 1.14-point difference, if maintained for eight years, would yield 9.33 percent more income per person, which is a lot more than almost anyone can expect from a tax cut."