In separate testimony to Financial Crisis Inquiry Commission, officers of Clayton Holdings—the largest residential loan due diligence and securitization surveillance company in the United States and Europe—testified that Clayton's review of over 900,000 mortgages issued from January 2006 to June 2007 revealed that scarcely 54% of the loans met their originators’ underwriting standards. How many investment and commercial banks were included in Clayton Holdings' analysis of January 2006 to June 2007 loans?