There's an old saying in the stock market: sell in May and go away. Now that the first of May is here should we sell?
A lot of studies have been done on this saying. A famous study published in the American Economic Review in 2002 found that, yes, this phenomenon does exist and that returns on stock markets in 36 out of 37 countries studied from 1970 to 1998 were higher in the November to April period than they were in the May to October period.
But a study published in Econ Journal Watch in 2004 attributed the higher return to a couple of extreme data points, in particular the October 1987 crash in world equity prices and the August 1998 collapse of Long Term Capital Markets. These people found no economically exploitable opportunity in the S&P 500 futures market based on that strategy. However, it did find that more major economic and political events seem to take place during May to October period.