In this study we examine the temporal dynamics of dealer market share and their ramification for competition and trading costs using a large sample of NASDAQ securities. Our results show that although the total market share of the top five dealers is relatively stable over time, there is significant monthly variation in the composition of the top five dealers. We show that market share turbulence among top dealers is another form of competition that narrows bid–ask spreads, especially for stocks with less competitive market structure.

In this study we show that both the price impact of trades and serial correlation in trade direction are positively and significantly related to the probability of information-based trading (PIN). The positive relation remains significant even after controlling for the effects of stock attributes. Higher trading activity (i.e., shorter intervals between trades) induces both larger price impact and stronger positive serial correlation in trade direction. The effect of time interval between trades on quote revision is stronger for stocks with higher PIN values. These results provide direct empirical support for the information models of trade and quote revision.