RT Journal Article SR Electronic T1 Investment rules, margin, and market volatility JF The Journal of Portfolio Management FD Institutional Investor Journals SP 45 OP 52 DO 10.3905/jpm.1989.409233 VO 16 IS 1 A1 Gew-rae Kim A1 Harry M. Markowitz YR 1989 UL https://pm-research.com/content/16/1/45.abstract AB