Economic Scene: Which Party in the White House Means Good Times for Investors?:I guess it's possible that Republicans always manage to get voted out of office just as their brilliant economic policies are taking effect, or that they're really, really unluckly.
"Professors Santa-Clara and Valkanov look at the excess market return - the difference between a broad index of stock prices (similar to the Standard & Poor's 500-stock index) and the three-month Treasury bill rate - between 1927 and 1998. The excess return measures how attractive stock investments are compared with completely safe investments like short-term T-bills.
Using this measure, they find that during those 72 years the stock market returned about 11 percent more a year under Democratic presidents and 2 percent more under Republicans - a striking difference."
But I wouldn't bet on it.