Betting on price momentum

“Don’t fight the tape.”

“Make the trend your friend.”

“Cut your losses and let your winners run.”

“These Wall Street maxims all mean the same thing—bet on price momentum. Of all the beliefs on Wall Street, price momentum makes efficient market theorists howl the loudest. The defining principle of their theory is that you cannot use past prices to predict future prices. A stock may triple in a year, but according to efficient market theory, that will not affect next year. Efficient market theorists also hate price momentum because it is independent of all accounting variables. If buying winning stocks works, then stock prices have “memories” and carry useful information about the future direction of a stock.”

James O’Shaughnessy, What Works on Wall Street: A Guide to the Best-Performing Investment Strategies of All Time 1st Edition (1996) 


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