Regardless of the sustainability of 6.5% real returns in the future, nobody would dispute that it is hardly a“constant”, especially for short‐term horizons.
If we remain in an in‐sample framework, we can obtain R2s that are much better than 25%.
Although total corporate profits and S and P 500 profits are not the same thing, their growth rate is rather similar over long time periods (3.23% per year for total corporate profits vs. 3.17% for S and P 500 profits between 1947 and 2008):
Although there seems to be a long‐term elasticity of one between equity real returns and realized economic growth, changes in long‐term growth expectations and/or risk premia can have a huge impact on valuations. If we simply look at the Gordon‐Shapiro model and assume a denominator (expected rate of return – expected growth) of around 5%, a 1% decrease in long‐term expected growth decreases the value of equities by 20%. We believe that this explains much of equities’ “excess volatility puzzle”.
Additionally, it is important to note that this brief study concerns only the United States, a country that won two world wars and avoided socialist experiments during the last century. It would be interesting to calculate the trend of the real equity return / real GDP ratio for other countries. Unfortunately, reliable data on long‐term real returns is hard to obtain for most countries, as they generally originate in the early 1970s (e.g. MSCI Indices).