We find that profit-warning announcements elicit a strong negative market response that is not sensitive to timing the warning in advance of the earnings announcement. Share prices begin to adjust about five days before a profit warning, and the market response is not complete until about five days after the warning. The accumulated response over the 11-day period ending five days after the announcement is -21.7%. The profit warning effect over the two-day announcement period is 32 times the valuation effect upon subsequent release of the actual earnings. There is no evidence of a reversal after this period, and therefore no sign that the market response is excessive.

Profit warnings
Financial Review
Sprott School of Business

Jackson, D, & Madura, J. (Jeff). (2003). Profit warnings and timing. Financial Review, 38(4), 497–513. doi:10.1111/1540-6288.00057