Unlike certain authors, I am not promoting some agenda about where stocks will be at some future date! Instead, I am just including a couple of excerpts from a paper by luminaries David Blanchett, Michael Finke, and Wade Pfau that suggests that stocks are the right investment for the long run—based on historical research. Their findings are actually fairly broad and call market efficiency into question.
We find strong historical evidence to support the notion that a higher allocation to equities is optimal for investors with longer time horizons, and that the time diversification effect is relatively consistent across countries and that it persists for different levels of risk aversion.
When they examine optimal equity weightings in a portfolio by time horizon, the findings are rather striking. Here’s a reproduction of one of their figures from the paper:
Source: SSRN/Blanchett, Finke, Pfau (click to enlarge)
They describe the findings very simply:
Figure 1 also demonstrates how to interpret the results we include later in Tables 2 and 3. In Figure 1 we note an intercept (α) of 45.02% (which we will assume is 45% for simplicity purposes) and a slope (β) of .0299 (which for simplicity purposes we will assume is .03). Therefore the optimal historical allocation to equities for an investor with a 5 year holding period would be 60% stocks, which would be determined by: 45% + 5(3%) = 60%.
In other words, if your holding period is 15-20 years or longer, the optimal portfolio is 100% stocks!
Reality, of course, can be different from statistical probability, but their point is that it makes sense to own a greater percentage of stocks the longer your time horizon is. The equity risk premium—the little extra boost in returns you tend to get from owning stocks—is both persistent and decently high, enough to make owning stocks a good long-term bet.