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Krugman's contention (that the growth of a commercial real estate bubble indicates that U.S. housing policy was not the cause of the crisis) is challenged by additional analysis. After researching the default of commercial loans during the financial crisis, Xudong An and Anthony B. Sanders reported (in December 2010): "We find limited evidence that substantial deterioration in CMBS [commercial mortgage-backed securities] loan underwriting occurred prior to the crisis." Other analysts support the contention that the crisis in commercial real estate and related lending took place after the crisis in residential real estate. Business journalist Kimberly Amadeo reports: "The first signs of decline in residential real estate occurred in 2006. Three years later, commercial real estate started feeling the effects. Denice A. Gierach, a real estate attorney and CPA, wrote:

What are CMBS?
commercial mortgage-backed securities