Credit Regimes and the Seeds of Crisis

This paper presents a theory of mortgage credit that explains (1) the rise of non-prime lending during the early 2000’s, (2) the simultaneous housing boom, and (3) the subsequent crisis. The theory is built on rational and competitive behavior by lenders in response to asymmetric information about borrower income risk. Two possible credit regimes may arise. In the “screening” regime, lenders ration credit through documentation requirements (screening contracts) and down-payment requirements (separating contracts). In the alternative “pooling” regime, risky borrowers gain access to low-doc low-down mortgages (pooling contracts). Joint housing and mortgage market equilibrium implies a tipping point phenomenon — a fall in income risk can trigger the pooling regime, lead to a sudden fall in documentation requirements, and, due to an indifference condition switching effect, generate a rapid appreciation in home prices. A housing crisis follows this credit-fueled boom once fundamentals revert and the screening regime returns. The theory matches microeconomic evidence on the allocation of credit during the mid-2000’s, explains why mortgage rates fell relative to treasury yields during 2003, and provides a framework to assess policies intended to rule out future housing crises.