Investment research firm Morningstar considers the question of how to tell if you've got the right proportion of stocks and bonds (or stock and bond mutual funds) in your portfolio.

This ratio can be the single biggest factor determining how well your portfolio performs, so it's something you want to pay attention to.

The article looks at target-date mutual funds, which are designed to be an all-in-one solution for people looking to retire in a given year. These funds automatically alter the mix of stocks and bonds they hold as a person nears retirement, focusing more on income and less on growth investments that may be riskier.