The Failure of Models that Predict Failure: Distance, Incentives and Defaults
Stephen M. Ross School of Business, University of Michigan
University of Chicago - Booth School of Business
London Business School
August 1, 2010
Chicago GSB Research Paper No. 08-19
EFA 2009 Bergen Meetings Paper
Ross School of Business Paper No. 1122
Statistical default models, widely used to assess default risk, are subject to a Lucas critique. We demonstrate this phenomenon using data on securitized subprime mortgages issued in the period 1997--2006. As the level of securitization increases, lenders have an incentive to originate loans that rate high based on characteristics that are reported to investors, even if other unreported variables imply a lower borrower quality. Consistent with this behavior, we find that over time lenders set interest rates only on the basis of variables that are reported to investors, ignoring other credit-relevant information. The change in lender behavior alters the data generating process by transforming the mapping from observables to loan defaults. To illustrate this effect, we show that a statistical default model estimated in a low securitization period breaks down in a high securitization period in a systematic manner: it underpredicts defaults among borrowers for whom soft information is more valuable. Regulations that rely on such models to assess default risk may therefore be undermined by the actions of market participants.
Number of Pages in PDF File: 46
Keywords: Securitization, screening, incentives, subprime, defaults, mortgages, disintermediation, models, lucas critique, soft information, hard information, failure, predictability
JEL Classification: G21
Date posted: November 10, 2008 ; Last revised: August 15, 2010
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