Trades outside the quotes: Reporting delay,trading option,or trade size?

In the period 1993 through 2002 examined in this study, quoted and effective spreads declined substantially on Nasdaq and to a lesser degree on the NYSE. At the same time, however, trades outside the quotes increased dramatically on Nasdaq. Because investors would prefer to trade at the quotes rather than outside the quotes, we examine why trades outside the quotes are observed. We focus on how the continuous market mechanism itself influences the outcome of orders and the reporting of trades, and we conclude that slippage exists in the market mechanism. Outside-trades occur on Nasdaq, first, because of delays in reporting trades, second, because the ability of dealers to delay execution of trades creates a look-back option, which when exercised results in outside-trades, and third, because large trades can take place at prices outside the quotes. Outside-trades are rarely observed on the NYSE because the market is more centralized. While the pattern of trading on the NYSE is not inconsistent with the presence of a look-back option, our tests provide no direct evidence that specialists are exercising such an option.