SAN FRANCISCO (MarketWatch) -- Complex derivatives, such as mortgage-backed securities and collateralized debt obligations, have probably helped subprime problems spread across much of the financial sector, possibly affecting economic activity, Federal Reserve official Janet Yellen said on Monday.
Mortgage-backed securities (MBS) are packages of home loans that are sliced up into different bits and sold to institutional investors. Collateralized debt obligations repackage MBS and other asset-backed securities into yet more securities for sale.
These relatively new derivatives and other financial innovations helped fuel the housing boom. They were hailed as beneficial instruments because they encouraged the wider spread of risk among a more diverse set of investors. Other examples include collateralized loan obligations and credit default swaps.
But Yellen said on Monday that the subprime mortgage crisis has raised questions about the impact of these derivatives.
"It ... may turn out that these innovations don't actually spread risk as transparently or effectively as once thought," she said during a speech at the annual meeting of the National Association for Business Economics in San Francisco.
If that's the case, it could have a big knock-on effect on financial markets and the economy, she added.
"This would mean -- to some extent -- a more or less permanent reduction of credit flowing to risky borrowers and long-lasting shifts in patterns of financial intermediation," Yellen explained. "It could also mean an increase in risk premiums throughout the economy that persists even after this turbulent period has passed."
By spreading and diversifying risks, instruments like MBS and CDOs may have increased the chances that disruptions in small parts of the financial world have a broader impact.
The subprime mortgage market is only 10% to 15% of the overall home loan industry, Yellen noted.
"How, then, could problems in this relatively small market infect so much of the financial sector, and possibly real economic activity?" Yellen asked. "The answer appears to lie in the characteristics of some of the complex financial instruments that have been developed as a means to diversify and spread risk."