Although examination letters are part of the supervisory process, they are not considered enforcement actions, which carry more weight. Scott, the Fitch senior director, called the firm's new risk team impressive, but "they inherited a lot of problems." The problems cut into Citigroup's all-important capital base. When it comes to valuing that base, regulators and credit rating agencies favor using common stock. But Citigroup, beginning in late 2007, relied increasingly on "hybrid" capital forms, such as trust-preferred securities, to prop up its Tier 1 ratio.