The Great Divide over Market Efficiency

Clifford Asness and John Liew have an excellent piece in Institutional Investor on Fama, Shiller and The Great Divide over Market Efficiency. Asness and Liew are both students of Fama so you might expect them to come down squarely on the side of market efficiency but they are also co-founders of AQR Capital, an asset management firm ($100 billion under management) with an unusually empirically driven approach to investing. In addition to publishing and using its own research, for example, AQR sponsors the AQR Insight Award which:

…recognizes important, unpublished papers that provide the most significant, new practical insights for tax-exempt institutional or taxable investor portfolios.

The Insight award is worth up to $100,000 so the firm is serious in thinking that research can be profitable.

Asness and Liew argue that just a few anomalies are robust across time, countries, and asset markets, notably momentum and value. On value, they note that a trading strategy of high minus low, that is long a portfolio of cheap stocks (high book value to price) and short a portfolio of expensive stocks (low book value to price) has generated consistently high returns relative to (CAPM) risk over time, albeit not without occasional terrifying episodes.

The efficient market explanation is that book value to price is a stand-in for a non-diversifiable risk factor. The behavioral story is that “a lot of individuals and groups (particularly committees) have a strong tendency to rely on three-to five-year performance evaluation horizons.” As a result, they chase “winners” and flee “losers” over a 3-5 year horizon which generates momentum and the mispricing that makes the value strategy successful. As Asness and Liew put it “investors act like momentum traders over a value time horizon.”

Asness and Liew then follow up with a very astute counter-argument to the risk-factor story:

Also, many practitioners offer value-tilted products and long-short products that go long value stocks and short growth stocks. But if value works because of risk, there should be a market for people who want the opposite. That is, real risk has to hurt. People should want insurance against things like that. Some should desire to give up return to lower their exposure to this risk. However, we know of nobody offering the systematic opposite product (long expensive, short cheap)…the complete lack of such products is  a bit vexing for the pure rational based risk-based story.

Lots of other history and insights.


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