This paper examines the growth of electronic communication networks (ECNs) and their competitive impact on the Nasdaq. We find that the development of these alternative trading platforms is associated with tighter quoted, effective, and relative bid–ask spreads, greater depths, and less concentrated markets. Further, our results show that an increase in ECN trading may have caused some traditional market makers (wholesaler and national retail dealers) to exit the market for market making. Overall, our results suggest that ECNs provide a source of competition to traditional Nasdaq dealers.

Abstract Aggregate idiosyncratic volatility spiked nearly fivefold during the Internet boom of the late 1990s, dwarfing in magnitude a moderately increasing trend. While some researchers argue that this rise in idiosyncratic risk was the result of changes in the characteristics of public firms, others argue that it was driven by the changing sentiment of irrational traders. We present evidence that the marketwide decline in maturity of the typical public firm can explain most of the increase in firm-specific risk during the Internet boom. Controlling for firm maturity, we find no evidence that investor sentiment drives idiosyncratic risk throughout the Internet boom.