RT Journal Article SR Electronic T1 Bond ratings versus market risk premiums JF The Journal of Portfolio Management FD Institutional Investor Journals SP 64 OP 69 DO 10.3905/jpm.1980.408743 VO 6 IS 3 A1 Eric H. Sorensen YR 1980 UL https://pm-research.com/content/6/3/64.abstract AB