Associate Professor of Finance, Pedro Santa-Clara at UCLA has written a very interesting paper on the popular "myth" that the stockmarket does better under Republicans than Democrats.
"Using data since 1927, we find that the average excess return of the value-weighted CRSP index over the 3-month Treasury bill rate has been about 2% under Republican and 11% under Democratic presidents - - - a striking difference of 9% per year! This difference is economically and statistically significant. A decomposition of excess returns reveals that the difference is due to real market returns being higher under Democrats by more than 5%, as well as to real interest rates being almost 4% lower under Democrats. The results are even more impressive for the equal-weighted portfolio, where the difference in excess returns between Republicans and Democrats reaches 16%."
From The Journal of Finance, Volume LVIII, No. 5; October 2003
"Using data since 1927, we find that the average excess return of the value-weighted CRSP index over the 3-month Treasury bill rate has been about 2% under Republican and 11% under Democratic presidents - - - a striking difference of 9% per year! This difference is economically and statistically significant. A decomposition of excess returns reveals that the difference is due to real market returns being higher under Democrats by more than 5%, as well as to real interest rates being almost 4% lower under Democrats. The results are even more impressive for the equal-weighted portfolio, where the difference in excess returns between Republicans and Democrats reaches 16%."
From The Journal of Finance, Volume LVIII, No. 5; October 2003