Abstract We test the hypothesis that insider trading impairs market liquidity by analyzing intraday trades and quotes around 1,497 IPO lockup expirations in the period 1995–1999. We find that, while lockup expirations are associated with considerable insider trading for some IPO firms, they have little effect on effective spreads. By contrast, two other liquidity measures, quote depth and trading activity, improve substantially. In the 23% of lockup expirations where insiders disclose share sales, spreads actually decline. These findings indicate that a large body of well-informed, blockholding insider traders can enter a market from which they had previously been absent, and substantially change trading volume and share price without impairing market liquidity.

Abstract Consistent with institutions having an advantage over individuals, we find that newly public firms with the highest levels of institutional investment significantly outperform those with the lowest levels. While prior literature has attributed much of institutions’ higher returns around various corporate events to private information, we find that much of the difference simply reflects better interpretation of readily available public information. Individuals disproportionately invest in the types of firms that earn significantly lower abnormal returns over the long run. Individuals either disregard or misinterpret the relevance of readily available public information, and as a result, they bear the brunt of IPO underperformance.

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