Critics such as economist Paul Krugman and U.S. Treasury Secretary Timothy Geithner have argued that the regulatory framework did not keep pace with financial innovation, such as the increasing importance of the shadow banking system, derivatives and off-balance sheet financing. A recent OECD study suggest that bank regulation based on the Basel accords encourage unconventional business practices and contributed to or even reinforced the financial crisis. In other cases, laws were changed or enforcement weakened in parts of the financial system. Key examples include: