An ‘irrational exuberance’ indicator shows the stock market is off the charts compared with the top of the internet bubble

Irrational exuberance is alive and well on Wall Street, according to a valuation model proposed by former Federal Reserve Chairman Alan Greenspan.

The model in question is not the one you’re probably thinking.

The story of how Greenspan came to use the phrase “irrational exuberance” is well-known and widely repeated: He first used it in a…