The Paris Bourse (currently Euronext Paris) refined its trading system to include electronic call auctions at market closings in 1996 for its less-liquid Continuous B stocks and in 1998 for its more actively traded Continuous A stocks. This paper analyzes the effects of the innovation on market quality. Our empirical analysis of price behavior for two samples of firms (50 B stocks and 50 A stocks) for two different calendar dates (1996 and 1998) indicates that introduction of the closing calls has lowered execution costs for individual participants and sharpened price discovery for the broad market. We further observe that market quality is improved at market openings, albeit to a lesser extent. We suggest that a positive spillover effect explains the closing call's more pervasive impact.

This paper considers how estimates of the market model beta parameter can be biased by friction in the trading process (information, decision, and transaction costs) that (a) leads to a distinction between observed and ‘true’ returns; (b) causes observed returns to be generated asynchronously for a set of interdependent securities; and (c) thereby introduces serial cross-correlation into security returns. Several propositions are derived from which consistent estimators of beta are obtained, and the effect of differencing interval length on beta estimates is specified. The formulation is contrasted with the related analyses of Scholes-Williams (1977) and Dimson (1979).