This is the sixth installment in our series on how individual investors can assess their financial health.

Diversification is a perennial topic among investors, and if it seems controversial at times, that may be due to the fact that people don’t always share the same understanding of what it means. But diversification isn’t about investing in a certain number of securities or funds. And it’s not about investing in every possible security under the sun.

Diversification and Risk

Simply put, diversification is the process of combining investments that don’t move in lockstep with each other. For example, Treasury bonds tend to do well when stocks are falling, and vice versa.  Combining stocks and bonds thus helps to limit risk.  Bonds also reduce the risk of a portfolio because they tend to be less risky on a standalone basis than stocks.

This brings us to an important point: the aggregate risk/return properties of a portfolio depend not only on the risk and return of the assets themselves, but also on the relationships between them.  Determining the right balance among these three factors (asset risk, asset return, and diversification benefit) is the challenge of diversification.

A Diversification Self-Assessment

The starting point in the determining whether your portfolio is properly diversified is to come up with a risk level that matches your needs.  I discussed risk estimation in last week’s blog .  Assuming you have a target risk level for your portfolio, you can then attempt to determine how to combine assets so as to achieve the maximum expected return for this risk.

The word “expected” is crucial here.  It is easy to look back and to see, for example, that simply holding 100% of your assets in U.S. stocks would have been a winning strategy over the past five years or so.  The trailing five year return of the S&P 500 is 15.7% per year and there has not been a 10% drop in over 1,000 days .  Over this period, holding assets in almost any other asset class has only reduced portfolio return and risk reduction does not look like a critical issue when volatility is this low.  The problem, of course, is that you invest on the basis of expected future returns and you have to account for the fact that there is enormous uncertainty as to what U.S. stocks will do going forward. Diversification is important because we have limited insight into the future.

Many investors think that they are diversified because they own a number of different funds.  Owning multiple funds that tend to move together may result in no diversification benefit at all, however.  A recent analysis of more than 1,000,000 individual investors found that their portfolios were substantially under-diversified.  The level of under-diversification, the authors estimated, could result in a reduction of lifetime wealth accumulation of almost one fifth (19%).

Additional Diversifiers

Aside from a broad U.S. stock index (S&P 500, e.g. IVV or VFINX) and a broad bond index (e.g. AGG or VBMFX), what other asset classes are worth considering?

• Because the S&P 500 is oriented to very large companies, consider adding an allocation to small cap stocks. such as with a Russell 2000 index (e.g. IWM or NAESX).
• There is also considerable research that suggests that value stocks —those stocks with relatively low price-to-earnings or price-to-book values—have historically added to performance as well. A large cap value fund (e.g. VTV, IWD, VIVAX) or small cap value fund (e.g. VBR, RZV) may be a useful addition to a portfolio.
• In addition to domestic stocks, consider some allocation to international stocks (e.g. EFA or VGTSX) and emerging markets (e.g. EEM or VEIEX).
• Real Estate Investment Trusts (REITs) invest in commercial and residential real estate, giving investors share in the rents on these properties. There are a number of REIT index funds (e.g. ICF, RWR, and VGSIX).
• Utility stock index funds (e.g. XLU) can be a useful diversifier because they have properties of stocks (shareholders own a piece of the company) and bonds (utilities tend to pay a stable amount of income), but have fairly low correlation to both.
• Preferred shares (as represented by a fund such as PFF) also have some properties of stocks and some of bonds.
• Another potential diversifier is gold (GLD).

Diversification Example

To help illustrate the potential value of diversification, I used a portfolio simulation tool (Quantext Portfolio Planner. which I designed) to estimate how much additional return one might expect from adding a number of the asset classes listed above to a portfolio that originally consists of just an S&P 500 fund and a bond fund.

Risk and return for a 2-asset portfolio as compared with a more diversified portfolio (source: author’s calculations)

The estimated return of a portfolio that is 70% allocated to the S&P 500 and 30% allocated to an aggregate bond index fund is 6.4% per year with volatility of 13%.  (Volatility is a standard measure of risk.)  Compare that to the more diversified portfolio I designed, which has the same expected volatility, but an expected return of 7.3% per year, as estimated by the portfolio simulation tool.  The diversified portfolio is not designed or intended to be an optimal portfolio, but rather simply to show how a moderate allocation to a number of other asset classes can increase expected return without increasing portfolio risk.[1]

The process of analyzing diversified portfolios can get quite involved and there are many ideas about how best to do so.  But the range of analysis suggests that a well-diversified portfolio could add 1%-2% per year to portfolio return.

I have observed that the longer a bull market in U.S. stocks goes on, the more financial writers will opine that diversifying across asset classes is pointless.  We are in just that situation now, as witnessed by a recent article on SeekingAlpha titled Retirees, All You Need is the S&P 500 and Cash .

On the other hand, there is a large body of research that demonstrates that, over longer periods, diversification is valuable in managing risk and enhancing returns.  That said, a simple allocation to stocks and bonds has the virtue of simplicity and can be attained with very low cost.  Diversifying beyond these two assets can meaningfully increase return or reduce risk, but an increase in average return of 1%-2% per year is not going to take the sting out of a 20%+ market decline.  What’s more, a diversified portfolio is quite likely to substantially under-perform the best-performing asset class in any given time period.

But over long periods of time, the gain of 1%-2% from diversification is likely to increase your wealth accumulation over 30 years by 20%-30% .  This is consistent with the analysis of 1,000,000 individual investors cited above, from which the authors concluded that under-diversified portfolios were likely to reduce lifetime wealth accumulation by 19%.

For investors seeking to diversify beyond a low cost stock-bond mix, there are a number of simple portfolios that include a range of the asset classes discussed here and that have fairly long track records.  These are worth exploring as a template for further diversifying your own portfolio.

[1] For details on how the model estimates risk and return for different asset classes and for portfolios, see the whitepaper I wrote on the subject.

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