A Structural Model of Short-Term Reversals

Abstract

We present a structural model of the stock market where a subset of the investors is infrequently present at the market. In our model the stocks’ return reversal pattern is exponential and the amount of return reversal, the speed of return reversal and stock’s transitory volatility are all related to liquidity. In contrast to common perception, fast return reversal is typically a sign of inefficient, illiquid markets, thus not a sign of efficiency. Other results are that the stock’s return liquidity premium and the cost of immediacy to transitory investors are non-monotonic in several structural parameters of the model, such as the number of market makers. Based on the entire available return history for NYSE and Amex traded stocks, we find that, on average, 24% of NYSE and Amex traded stocks’ excess returns revert within a week, that the pattern of return reversal is exponential, and that nearly 20% of daily volatility is transitory. Both the speed of return reversal and the amount of transitory volatility depend on the stock’s liquidity: For illiquid stocks, return reversals are faster and a greater amount of the volatility, 27%, is transitory. Our estimates of the total costs of immediacy suffered by investors, as a percentage of stock’s market capitalization, are non-monotonic in stock’s liquidity.