By Brent Everett
Bill Bernstein, in his excellent recent book Deep Risk, discusses the important distinction between two types of risk: deep and shallow. Shallow risk, such as market volatility, is the major concern for most investors. It's also well measured by standard deviation, a key concept in the Markowitz mean-variance framework that's the basis for Modern Portfolio Theory. However, this completely ignores what most people that are attempting to accumulate wealth for eventual retirement should be concerned about.