What moves stock prices around credit rating changes?

Abstract

Using monthly and multi-day return windows, research shows that credit rating downgrades often reveal new information and lead to significant stock price reactions but that upgrades do not. Using intraday data, we revisit these findings and extend them by examining the possibility of informed trading ahead of the announcement of credit rating changes. Credit rating agencies delay public announcements of rating changes to provide issuers with time to review and respond to rating reports, which opens the door for informed trading in advance of credit rating changes. Using data on rating changes from S&P, Moody’s, and Fitch, we find a more modest price reaction to rating downgrades than documented elsewhere and show that stock prices respond to changes in long-term issuer ratings but not to changes in ratings of a single instrument or a subset of instruments. Most interestingly, we find that prices start moving before a downgrade announcement, controlling for other news and investor anticipation. These pre-announcement movements are concentrated among observations where credit analysts are motivated to disclose private information to advance their careers. The beneficiaries of these disclosures appear to be institutional investors.