RT Journal Article SR Electronic T1 Trading Volume and Beta Stability JF The Journal of Portfolio Management FD Institutional Investor Journals SP 60 OP 64 DO 10.3905/jpm.1981.408797 VO 7 IS 2 A1 Michael D. Carpenter A1 David E. Upton YR 1981 UL https://pm-research.com/content/7/2/60.abstract AB