Why 'sell in May' worked and what to do now

Traders work on the floor of the New York Stock Exchange.
Lucas Jackson | Reuters

Jeffrey Hirsch, editor of the Stock Trader's Almanac and the website based on the book, explains below why the "sell in May" theory he and his father, Yale, popularized worked this year and whether investors should in fact stay away until the end of October as the maxim dictates.

If you deployed the strategy of selling at the end of April and then buying back the S&P 500 before November since 1950 you would have tripled your returns compared to just buying and holding stocks the whole year, according to Hirsch.

Here's Hirsch on how the theory works and why it made money this year...