A blog on financial markets and their regulation
Heterogeneous investors and multi factor models
January 3, 2015Posted by on
I read two papers last week that introduced heterogeneous investors into multi factor asset pricing models. The papers help produce a better understanding of momentum and value but they seem to raise as many questions as they answer. The easier paper is A Tug of War: Overnight Versus Intraday Expected Returns by Dong Lou, Christopher Polk, and Spyros Skouras. They show that:
100% of the abnormal returns on momentum strategies occur overnight; in stark contrast, the average intraday component of momentum profits is economically and statistically insignificant. … In stark contrast, the profits on size and value … occur entirely intraday; on average, the overnight components of the profits on these two strategies are economically and statistically insignificant.
The paper also presents some evidence that “is consistent with the notion that institutions tend to trade intraday while individuals are more likely to trade overnight.” In my view, their evidence is suggestive but by no means compelling. The authors also claim that individuals trade with momentum while institutions trade against it. If momentum is not a risk factor but a free lunch, then this would imply that individuals are smart investors.
The NBER working paper (Capital Share Risk and Shareholder Heterogeneity in U.S. Stock Pricing) by Martin Lettau, Sydney C. Ludvigson and Sai Ma presents a more complex story. They claim that rich investors (those in the highest deciles of the wealth distribution) invest disproportionately in value stocks, while those in lower wealth deciles invest more in momentum stocks. They then examine what happens to the two classes of investors when there is a shift in the share of income in the economy going to capital as opposed to labour. Richer investors derive most of their income from capital and an increase in the capital share benefits them. On the other hand, investors from lower deciles of wealth derive most of their income from labour and an increase in the capital share hurts them.
Finally, the authors show very strong empirical evidence that the value factor is positively correlated with the capital share while momentum is negatively correlated. This would produce a risk based explanation of both factors. Value stocks lose money when the capital share is moving against the rich investors who invest in value and therefore these stocks must earn a risk premium. Similarly, momentum stocks lose money when the capital share is moving against the poor investors who invest in momentum and therefore these stocks must also earn a risk premium.
The different portfolio choices of the rich and the poor is plausible but not backed by any firm data. The direction of causality may well be in the opposite direction: Warren Buffet became rich by buying value stocks; he did not invest in value because he was rich.
But the more serious problem with their story is that it implies that both rich and poor investors are irrational in opposite ways. If their story is correct, then the rich must invest in momentum stocks to hedge capital share risk. For the same reason, the poor should invest in value stocks. In an efficient market, investors should not earn a risk premium for stupid portfolio choices. (Even in a world of homogeneous investors, it is well known that a combination of value and momentum has a better risk-return profile than either by itself: see for example, Asness, C. S., Moskowitz, T. J. and Pedersen, L. H. (2013), Value and Momentum Everywhere. The Journal of Finance, 68: 929-985)