One item that has not been examined is by pulling money out of a fund while it is dropping and putting it back in at a lower price, there have performance gains by the entire fund. The fund managers have to sell some of the investments to 'redeem' shares that are being switched to other funds, and they have to repurchase investments, most likely at a lower price, to generate shares when the money comes back in... These will far exceed any trading costs. The 'frequent' traders have actually improved the returns for all. They are just looking at the trading costs (commissions, etc), not at the gains due to the manager's trading...
Cheers!
Jim
Cheers!
Jim