For the past several decades, the traditional 60 percent stock, 40 percent bond allocation has dominated the investment industry. But since 2000, interest rates have declined to historic lows at or near zero percent. While this has given bond returns an historic tailwind, it begs the question: Have bonds become an unproductive portfolio-allocation tool?

Shortly after I entered the investment industry in 1980, inflation had risen to double-digit levels. Fed Chairman Paul Volker made a decision to attack this problem by raising interest rates to record levels. From the 20-percent peak in 1982, the Fed-funds rate has declined to zero, creating the greatest bond bull market in history.