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We examine the market response to quarterly earnings announcements made during trading and non-trading hours on the NYSE and the NASDAQ. For non-trading-hours announcements, the opening trade on the NYSE impounds most of the price response, whereas for trading-hours announcement trades. In contrast, the first post-announcement trade on the NASDAQ impounds most of the price response regardless of announcement time. These results suggest that the different trading environments on the two exchanges (e.g., specialist versus dealer market, call auction versus continuous trading, etc.) may differ in their ability to impound information.
Greene et al. (Mon,) studied this question.