Many a market connoisseur can name two value investors. No points for guessing who those two are. But to the chagrin of Efficient Market Hypothesis (EMH) proponents, there are many value investors who have seen much success. Mario Gabelli is one such investor.
Gabelli was schooled in the Benjamin Graham tradition of value investing. Graham manually searched through flurries of financial data to find companies trading at discounts to their current assets minus their total liabilities (what he termed net-net companies). With today's databases of information and computational speed, such companies are identified before they become grossly undervalued.
So Gabelli created Private Market Value (PMV), which Bruce Greenwald calls a "value metric that is less easily uncovered than net-net but no less discriminating in its ability to identify underpriced securities".
The idea behind PMV, as defined by Gabelli, is to determine the value an informed industrialist would pay to purchase assets with similar characteristics. The principle behind PMV is that because the market price is determined based on the last trade, it's not necessarily a good gauge of what a knowledgeable buyer would pay for the company. PMV seeks to exploit any such differences, with the idea that eventually a catalyst will come along and bring the market price to PMV levels.