The title is misleading as the data presented clearly supports the advantages of selling in May and buying in Oct.   An investor gains over 8% by buying in Oct and selling in May while barely braking even by Buying in May and selling in Oct. Moreover there is almost always a significant drop in the market between May and Oct.  
So I am selling in May with my gains in hand and waiting for a drop 5% min average 15% so I can rejoin the  market.  If the selling persists I wait will my yearly gains safely in hand.