Bloomberg Opinion columnist Barry Ritholtz interviews Roger Ibbotson, a professor emeritus of finance at Yale University who serves as chairman and chief investment officer at Zebra Capital Management LLC. He was also the founder and chairman of Ibbotson Associates (now a Morningstar company) and executive director of the Center for Research in Security Prices, which helped transform finance into a field of empirical study. His latest book, “Popularity: A Bridge Between Classical and Behavioral Finance,” co-authored with Thomas M. Idzorek, Paul D. Kaplan and James X. Xiong, was published in January.