Sell in May and go away for stock?

Statistics shows that Dow Jones industrial average rises 7.4% from Nov. 1 through April 30 in average since 1950, while rises only 0.4% from May 1 to Oct 31. Market crashes often happen between May 1 and October 31. But you should not treat it as a law of nature. It is only meaningful for long term investors.
Reference:
http://www.usatoday.com/money/perfi/columnist/krantz/2011-05-17-sell-in-may-and-go-away_n.htm