If A Bubble Doesn't Pop, Is It A Bubble?

In February I considered if bubble risk for US stocks was elevated. My conclusion: Yes, it appeared that the market was unusually frothy, based on an econometric technique that takes a stab at quantifying the ebb and flow of irrational exuberance. As a sell signal, however, the analysis has been dead wrong this year. The S&P 500 is up more than 6% since that post appeared six months ago.