Morningstar of Chicago announced last week that its system for rating mutual funds, commonly known as the "star rating," will be altered this summer to include a broader number of categories, which the company hopes will render it more relevant to the way investors use mutual funds.

The company's system, introduced in 1985, gives funds a rating of between one and five stars. Many investors use the system, sometimes to the dismay of financial planners, as a key way to choose funds. And fund companies often boast of the ratings in their advertising.

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