Here's one explanation for a yo-yoing stock market that leaves millions of 401(k) holders biting their nails on a regular basis: The cost for an investor to buy and then sell a stock has fallen by half in the past decade, to 3.5 cents, as the New York Times notes today.
With costs this low, old fashioned speculation makes more sense than ever -- and so does new fangled high-frequency trading by powerful computers.