RT Journal Article SR Electronic T1 Two Tiers - But How Many Decisions? JF The Journal of Portfolio Management FD Institutional Investor Journals SP 5 OP 12 DO 10.3905/jpm.1976.5 VO 2 IS 3 A1 Marshall E. Blume YR 1976 UL https://pm-research.com/content/2/3/5.abstract AB