The migration upward as a result of a switch to global rating scales might not lead immediately to homogenized prices for similarly rated municipal bonds, market participants say.

"My bottom line is that risk hasn't changed, no matter what you call it," said Guy LeBas, fixed-income strategist at Janney Montgomery Scott LLC. "The risk of a given issuer isn't changed just because a rating agency has a different scale. If the markets are rational, then risk should be priced the same."

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