The intraday timing of rating changes

Using time stamps of Standard & Poor's rating changes, we examine the timing of rating changes in an intraday setting. Our evidence shows that although most rating changes occur during trading hours, the proportion of downgrades announced after regular trading hours is higher than that of upgrades. In addition, unexpected after-hour downgrades are associated with more negative stock returns and lower trading volume in comparison to those announced during trading hours. We also find that Standard & Poor's is more likely to announce downgrades after hours when downgrades are released on busy days with many concurrent rating announcements, when they concern financial firms, and when they are unexpected. In addition, Egan-Jones Ratings (EJR), an investor-paid credit rating agency, demonstrates a similar tendency in announcing downgrades after trading hours. This is the first study to document systematic differences in the timing of credit rating changes announced before and after the market closes. Our findings suggest that Standard & Poor's announces downgrades after trading hours to better disseminate information, and thus have important policy implications.