Twelve years ago Stanford professor Joseph Piotroski effectively demolished the Fama and French argument that the excess returns reaped by value investors should be thought of as a risk premium. Fama and French, like others before them, had rightly observed that a significant proportion of value stocks are actually “value traps”: bad firms headed for a worse future, cheap because they deserved to be. From this they concluded that value investors were simply being paid a higher return for the higher risks they incurred.
Piotroski dug deeper and found a very different story. (more…)