The above formula may be responsible for the onset of the financial crisis and our long slide into double-dip recession (or is it a Depression after all?). It is a Gaussian Copula. In finance it was used to model the risk in a set of debt papers (like mortgages) in credit default swaps. It was highly successful too. Until it was pushed past breaking point.
For five years, Li's formula, known as a Gaussian copula function, looked like an unambiguously positive breakthrough, a piece of financial technology that allowed hugely complex risks to be modeled with more ease and accuracy than ever before. With his brilliant spark of mathematical legerdemain, Li made it possible for traders to sell vast quantities of new securities, expanding financial markets to unimaginable levels.Forbes magazine calls it the formula from hell. Wired magazine has the longer, more in-depth coverage here.
His method was adopted by everybody from bond investors and Wall Street banks to ratings agencies and regulators. And it became so deeply entrenched—and was making people so much money—that warnings about its limitations were largely ignored.
Then the model fell apart. Cracks started appearing early on, when financial markets began behaving in ways that users of Li's formula hadn't expected. The cracks became full-fledged canyons in 2008—when ruptures in the financial system's foundation swallowed up trillions of dollars and put the survival of the global banking system in serious peril.