Black was right: Price is within a factor 2 of Value

TL;DR

This paper provides evidence that financial markets exhibit medium-term trending behavior and long-term mean reversion, supporting Black's hypothesis that prices are typically within a factor of two of their fundamental value, with implications for market dynamics.

Contribution

It offers empirical support for Black's intuition about price deviations and their slow correction, highlighting the coexistence of trend-following and mean-reverting behaviors in markets.

Findings

Markets trend over months and mean-revert over years.

Prices tend to be within a factor of 2 of fundamental value.

Mean reversion acts as a weak self-correcting mechanism.

Abstract

We provide further evidence that markets trend on the medium term (months) and mean-revert on the long term (several years). Our results bolster Black's intuition that prices tend to be off roughly by a factor of 2, and take years to equilibrate. The story behind these results fits well with the existence of two types of behaviour in financial markets: "chartists", who act as trend followers, and "fundamentalists", who set in when the price is clearly out of line. Mean-reversion is a self-correcting mechanism, tempering (albeit only weakly) the exuberance of financial markets.