Collateralized debt obligation CDOs
Collateralized debt obligations (CDOs) are a type of structured asset-backed security (ABS) whose value and payments are derived from a portfolio of fixed-income underlying assets. CDOs securities are split into different risk classes, or tranches, whereby "senior" tranches are considered the safest securities. Interest and principal payments are made in order of seniority, so that junior tranches offer higher coupon payments (and interest rates) or lower prices to compensate for additional default risk. A few academics, analysts and investors such as Warren Buffett and the IMF's former chief economist Raghuram Rajan warned that CDOs, other ABSs and other derivatives spread risk and uncertainty about the value of the underlying assets more widely, rather than reduce risk through diversification. Following the onset of the 2007-2008 credit crunch, this view has gained substantial credibility. Credit rating agencies failed to adequately account for large risks (like a nationwide collapse of housing values) when rating CDOs and other ABSs.