When you diversify, you aim to manage your risk by spreading out your investments. You can diversify both within and among different asset classes. You can also diversify within asset classes. In this case, you divide the money you’ve allocated to a particular asset class, such as stocks, among various categories of investments that belong to that asset class.


These smaller groups are called subclasses. For example, within the stock category you might choose subclasses based on different market capitalizations: some large companies or funds that invest in large companies, some mid-sized companies or funds that invest in them, and some small companies or funds that invest in them. You might also include securities issued by companies that represent different sectors of the economy, such as technology companies, manufacturing companies, pharmaceutical companies, and utility companies.


Similarly, if you’re buying bonds, you might choose bonds from different issuers—the federal government, state and local governments and corporations—as well as those with different terms and different credit ratings.


Diversification, with its emphasis on variety, allows you to manage non-systematic risk (company or industry risk) by tapping into the potential strength of different subclasses, which, like the larger asset classes, tend to do better in some periods than in others. For example, there are times when the performance of small company stock outpaces the performance of larger, more stable companies. And there are times when small company stock falters.


Similarly, there are periods when intermediate-term bonds—U.S. Treasury notes are a good example—provide a stronger return than short- or long-term bonds from the same issuer. Rather than trying to determine which bonds to buy at which time, there are different strategies you can use.


For example, you can buy bonds with different terms, or maturity dates. This approach involves investing roughly equivalent amounts in short-term and long-term bonds, weighting your portfolio at either end. It allows you to limit risk by having at least a portion of your total bond portfolio in whichever of those two subclasses is providing the stronger return.


Alternatively, you can buy bonds with the same term but different maturity dates. Instead of investing $15,000 in one note that will mature in 10 years, for instance, you invest $3,000 in a note maturing in two years, another $3,000 in a note maturing in four years, and so on.