This is a long read, but it's worth it. The metric can be calculated in FRED[2], and as a predictor of future returns, it outperforms all of the most common stock market valuation metrics, including cyclically-adjusted price-earnings (CAPE) ratio[3]. (Basically, the average investor portfolio allocation to equities versus bonds and cash is inversely correlated with future returns over the long-term. This works better than pure valuation models because it accounts for supply and demand dynamics.)
This is a long read, but it's worth it. The metric can be calculated in FRED[2], and as a predictor of future returns, it outperforms all of the most common stock market valuation metrics, including cyclically-adjusted price-earnings (CAPE) ratio[3]. (Basically, the average investor portfolio allocation to equities versus bonds and cash is inversely correlated with future returns over the long-term. This works better than pure valuation models because it accounts for supply and demand dynamics.)
[1]: http://www.philosophicaleconomics.com/2013/12/the-single-gre...
[2]: http://research.stlouisfed.org/fred2/graph/?g=qis
[3]: http://www.multpl.com/shiller-pe/