RT Journal Article SR Electronic T1 Corporate bond valuation and the term structure of credit spreads JF The Journal of Portfolio Management FD Institutional Investor Journals SP 52 OP 64 DO 10.3905/jpm.1991.409331 VO 17 IS 3 A1 Robert B Litterman A1 Thomas Iben YR 1991 UL https://pm-research.com/content/17/3/52.abstract AB