NEW YORK ( TheStreet) -- For decades, Morningstar's ratings have been a powerful force in the mutual fund industry. Funds that win a top five-star rating tend to attract assets, while most funds that receive a lowly one star soon go out of business.Fund companies with high grades are quick to mention them in advertisements. But academic studies have shown that the ratings don't necessarily provide reliable guidance. All too often, funds that won top grades have gone on to deliver mediocre results. Now, Morningstar has developed a new ranking system that will rate recommended funds as gold, silver or bronze. Should you ignore the new system? Not necessarily. There are good reasons to think that the latest approach could be a helpful predictor of future performance.