Seasonals, price adjustment delays and estimated systematic risk

Abstract

This article analyzed potential interactions between seasonals and price adjustment delays on estimated systematic risk. It was shown that seasonals in unobservable true security returns can induce inconsistencies into the generalized Scholes and Williams estimator of systematic risk. An alternative estimator was proposed that is consistent in the presence of seasonals in the unobservable true returns. The direction of induced bias is unpredictable a priori, thereby representing a potentially important research consideration in market efficiency tests using abnormal returns. NASDAQ and Dow Jones 30 Industrial return data for the period 1983–87 were used to evaluate the proposed estimator against the OLS and generalized Scholes and Williams (GSW) alternatives. The absolute difference between the GSW and our estimator, that is the seasonal-induced bias, for NASDAQ stocks was negatively correlated with market capitalization. Moreover, seasonal-induced bias was larger for NASDAQ stocks than more highly capitalized Dow stocks. These empirical findings indicate that seasonals and price adjustment delays can interact to bias estimated systematic risk, where price adjustment delays would be projected to be more acute for smaller capitalization stocks.