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Author:Bubb, Ryan 

Discussion Paper
Securitization and moral hazard: evidence from credit score cutoff rules
Mortgage originators use credit score cutoff rules to determine how carefully to screen loan applicants. Recent research has hypothesized that these cutoff rules result from a securitization rule of thumb. Under this theory, an observed jump in defaults at the cutoff would imply that securitization led to lax screening. We argue instead that originators adopted credit score cutoff rules in response to underwriting guidelines from Fannie Mae and Freddie Mac and offer a simple model that rationalizes such an origination rule of thumb. Under this alternative theory, jumps in default are not evidence that securitization caused lax screening. We examine loan-level data and find that the evidence is inconsistent with the securitization rule-of-thumb theory but consistent with the origination rule-of-thumb theory. There are jumps in the number of loans and in their default rate at credit score cutoffs in the absence of corresponding jumps in the securitization rate. We conclude that credit score cutoff rules provide evidence that large securitizers were to some extent able to regulate originators' screening behavior.
AUTHORS: Kaufman, Alex; Bubb, Ryan
DATE: 2011

Discussion Paper
Securitization and moral hazard: evidence from a lender cutoff rule
Credit score cutoff rules result in very similar potential borrowers being treated differently by mortgage lenders. Recent research has used variation induced by these rules to investigate the connection between securitization and lender moral hazard in the recent financial crisis. However, the conclusions of such research depend crucially on understanding the origin of these cutoff rules. We offer an equilibrium model in which cutoff rules are a rational response of lenders to per-applicant fixed costs in screening. We then demonstrate that our theory fits the data better than the main alternative theory already in the literature, which supposes cutoff rules are exogenously used by securitizers. Furthermore, we use our theory to interpret the cutoff rule evidence and conclude that mortgage securitizers were in fact aware of and attempted to mitigate the moral hazard problem posed by securitization.
AUTHORS: Bubb, Ryan; Kaufman, Alex
DATE: 2009

Working Paper
Further investigations into the origin of credit score cutoff rules
Keys, Mukherjee, and Vig (2010a) argue that the evidence presented in Bubb and Kaufman (2009) is based on an inappropriate pooling of loans sold to private-label securitizers with loans sold to the government sponsored enterprises (GSEs). In this paper we investigate the issues raised by the authors and conclude that they do not change our basic analytical approach or conclusions. We examine samples that do not pool together loans sold to these two types of purchasers?a sample of loans bought by the GSEs, a sample of loans originated in 2008?2009 after the private-label market collapsed, and a sample of jumbo loans?and find discontinuities in the number and default rate of loans at credit score cutoffs in the absence of corresponding discontinuities in the securitization rate. We also examine a key assumption underlying their estimates?that no loans are both at risk of being sold to the GSEs and at risk of being sold to private-label securitizers?and show that the data are inconsistent with that assumption. We find that 18 percent of conforming loans in our sample at some time switched between GSE and private-label ownership, demonstrating that the GSEs and private-label securitizers competed for the same loans. Additionally, we show that lender screening cutoffs grew steadily over the period 1997?2010 during which the private-label market rose and collapsed.
AUTHORS: Kaufman, Alex; Bubb, Ryan
DATE: 2011

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