Additionally, see my comments to boarder42 regarding the utter inapplicability of this study to REITs.
Utter inapplicibility is a pretty absurd statement. The real returns in US $ terms over the 150 yr sample across 30+ countries from Appendix G look like this:
Housing: 8.11% with a 15.83% standard deviation
Stocks : 7.84% with a 25.08% standard deviation
Its hard to comprehend the implications of such numbers. But as SeattleCPA says the optimal portfolio would be ~ 90% Real Estate/10% Stocks if those numbers hold up in the future. So by going with roughly a ~50/50 leaves a ton of room for error, i.e. additional leverage risk, market risk from the REIT being traded in the stock market, and just about anything you can think of.
I described earlier the entire basis set for the REIT comparison, and quoted the section of the study where the authors describe that REITs are more volatile, and more correlated with the stock market. If you want to ignore the authors' warning and misuse their data, go ahead.
I will also quote from the same section:
"...Comparing the solid and dashed lines in Figure 12,
the long-run levels of unlevered REIT and
housing returns are remarkably similar. The time trend also follows a similar pattern, especially
in France. The REIT returns, however, tend to be
somewhat more volatile—most likely because
they reflect changes in valuation of future earnings, as well as the current portfolio performance.
The REIT returns also seem to be affected by the general ups and downs of the stock market: for
example, the 1987 “Black Monday” crash and dot-com bust in the US, as well as the 1930s Great
Depression and 1960s stock crises in France. This suggests that the valuations of the fund’s housing
portfolios may be affected by general stock market sentiment.
Overall, the returns on real estate investment funds serve to confirm the general housing return
level in our dataset...."
REITs have such a small sample (basically 1 country over 35 years instead of 30 countries over 150 countries) that I will rely quite a bit on the performance of the underlying real estate, you can feel free not to as most will. I understand that I am outlier. Based on the whole section and graphs its obvious that they mean REITs will be somewhat more volatile than unlevered real estate NOT somewhat more volitile than stocks.
But if you offer your estimations of long term returns, deviations, and correlations for Stocks, REITs, and bonds that you think are better than using a 150 year history I would be happy to calculate an optimal portfolio for you. I already estimated that returns would at least 1% less per year for housing to account for taxes and volatility would be 30% higher to account for leverage inherent in REITS.