Credit Rating and Stock Return Comovement

Firms with similar credit ratings, especially junk-rated ones, tend to comove strongly in stock returns with each other, which is not fully explained by their exposures to systematic factors. Following a firm’s downgrade into the junk-grade group, it tends to comove much more strongly in stock returns with firms in the junk-grade group and less with those in the investment-grade group. There is no similar trend in comovement with either credit rating group in the one-year window prior to the downgrade, indicating that changes in comovement are unlikely driven by changes in fundamentals of affected firms. Finally, we find evidence consistent with the investor clientele effect explanation for excessive comovement related to credit ratings by examining a) how mutual funds with different credit preferences adjust their stock holdings of firms being downgraded into junk-grade ratings and b) how flows to mutual funds that tend to invest in junk-rated firms affect these firms’ stock returns and their comovement.