Entry, Exit, Market Makers, and the Bid-Ask Spread
研究纳斯达克全国市场上做市商进入和退出对买卖价差的影响，发现大规模进入（退出）显著降低（提高）价差，且对做市商少的股票影响更大，支持竞争性定价模型。
The probability of entry and exit of dealers on the NASDAQ National Market (NNM) is significantly affected by trading intensity, volatility and the quoted bid-ask spread. Entry and exit of market makers is a pervasive phenomenon. Large-scale entry (exit) is associated with substantial declines (increases) in quoted end-of-day inside spreads, even after controlling for the effects of changes in volume and volatility. The spread changes are larger in magnitude for issues with few market makers; however, even for issues with a large number of market makers, substantial changes in quoted spreads take place. The results are consistent with the competitive model of dealer pricing.