Here is a preliminary finding from my study. I tested one idea that I had read about in the past and knew it was probably true but wanted to see the data. The idea was "even if you are 70 year old widow that wants 100% safety, owning a little bit of stocks will have less risk than being 100% in fixed income". I run two portfolios with 2 year rebalancing. The returns are all
real (after inflation) returns and the data is from 1968 to 2016.
Fixed income was savings accounts from 1968 to 2005, then government bonds from the Brazil Treasury Direct program from 2006 to 2016. Stocks are the Bovespa and US stocks is the S&P500
Results could change if I notice problems in the data.
So having a little bit of stocks in the portfolio decreased the Max drawdown, almost doubled the compounded annual growth rate, decreased the average down year and increased the average return of up years. On the other hand, you had a few more losing years and standard deviation of returns was slighly higher. I would say that the drawbacks of owning a little bit of equities (a little more down years, even though they are smaller on average) are definetly worth it. Having a smaller max DD is also very nice;
Of course if the widow will panic and sell when stocks are down, then that strategy wont work. But the Brazilian data do seem to back up, at least mostly, that idea