The Capital Asset Pricing Model (CAPM) is a simple heuristic for thinking about market returns. Basically, the idea is that the main risk that you can’t diversify away from is collective ...

Greenwood, Robin, Mark S. Seasholes, and David Biery. "The Portfolio Improvement Rule and the CAPM." Harvard Business School Technical Note 216-027, October 2015. (Revised February 2016.) ...