Few mutual funds or ETFs consistently invest in the top quintile of value stocks, finds a new study of mutual fund portfolios, co-authored by business and finance professor Martin Lettau and doctoral candidate Paulo Manoel. The researchers analyzed a comprehensive database of thousands of funds and ETFs between 1980 and 2016, finding just two that met the criteria. Saying that the pattern has persisted at least since the early 1980s, Professor Lettau says they also found the same result when they used other value-related criteria, including price-to-earnings ratios, price-to-cash-flow ratios, and dividend yield. They suggest there's a behavioral cause, with investors and advisers shunning stocks that meet the criteria. A Columbia professor observes that the behavioral explanation is supported by his research finding that by the time a stock has a low price-to-book ratio, it may well have suffered years of poor price performance.