The downgrades left Portugal one notch above junk rating and Greece's creditworthiness below that of Egypt.

BBC: Portugal and Greece downgraded on debt worries

Credit-rating agencies will also examine how to judge the creditworthiness of these things.

FORBES: Fact and Comment

When they determine that a bond issuer's creditworthiness has improved and upgrade the bonds, he says, the next rating change is equally likely to be up or down.

ECONOMIST: Rating agencies

The rating agency in August 2011 issued a historic downgrade of U.S. creditworthiness and threatened to lower it even further.

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