Michael Covel speaks with Justin Fox. Fox is the executive editor at the Harvard Business Review Group. He writes a blog for hbr.org (http://blogs.hbr.org/fox/) and a monthly column for Time magazine. Fox is also the author of "The Myth Of The Rational Market: A History of Risk, Reward, and Delusion on Wall Street". Covel and Fox discuss Harry Markowitz, Bayesian statistics, and making smart decisions in an uncertain world using quantitative tools; stocks, beta, and the importance of making useful predictions; Commodities Corporation and trend following trading in the early 1970’s; why a market in which everyone was rationally anticipating the future would be a random market; Amos Hostetter; how the behavioral mindset started to unfold in the 1970’s; Eugene Fama and the efficient market hypothesis; the Capital Asset Pricing Model; why well-designed markets and well-informed investors are prone to manias and panics; and individuals making errors vs. the group getting it right. Justin Fox can be found on Twitter at @foxjust or on the web at byjustinfox.com.