Momentum and reversals: An alternative explanation by non-conserved quantities

Abstract

The momentum effect in stock trading means that stocks performing well in the past will do so in the future, too. A recent (seemingly) proof of it would be a big discovery: Stock prices would obey laws similar to the Newtonian equation of motion. However, using the recent result that stock prices are distinct from stock values, the whole mystery disappears without a trace. Stock prices fluctuate chaotically (in a mathematical sense). Therefore the momentum within stock prices is easily explained by a self-fulfilling prophecy as long as enough people believe in it. In the recent experimental "proof" of the momentum effect, stocks had been traded thousands of times. In generalizing the well-known average cost effect, we give a second quantitative explanation for the observed results.