Year Published
2003
Abstract
Mortgage terminations arise because borrowers exercise options. This paper investigates the
apparently irrational behavior of those borrowers who do not terminate their mortgages even
when the exercise value of the option is deeply in the money.
We develop an option-based empirical model to analyze this phenomenon -- the behavior
of irrational "woodheads." Of course we do not observe "woodheads" explicitly in any body of
data. Instead, we analyze the correlates of unobserved heterogeneity within a large sample of
mortgage holders. We develop an error correction maximum likelihood (ECML) estimator using
martingale transforms to estimate the competing risks of mortgage prepayment and default,
recognizing unobserved heterogeneity which is due in part to the behavior of "woodheads." The
extended model is clearly superior to alternatives on statistical grounds.
We then analyze the economic implications of this more powerful model. We analyze the
predictions of the model for the valuation and pricing of mortgage pools and mortgage-backed
securities. Based upon an extensive Monte Carlo simulation, we find that the ECML model yields
prices for seasoned mortgage pools that deviate by 0.3 to almost 3.0 percent from more primitive
estimates.
The results indicate the empirical importance of heterogeneity and the implications of
non-optimizing behavior for the valuation and pricing of mortgages and mortgage-backed
securities.
apparently irrational behavior of those borrowers who do not terminate their mortgages even
when the exercise value of the option is deeply in the money.
We develop an option-based empirical model to analyze this phenomenon -- the behavior
of irrational "woodheads." Of course we do not observe "woodheads" explicitly in any body of
data. Instead, we analyze the correlates of unobserved heterogeneity within a large sample of
mortgage holders. We develop an error correction maximum likelihood (ECML) estimator using
martingale transforms to estimate the competing risks of mortgage prepayment and default,
recognizing unobserved heterogeneity which is due in part to the behavior of "woodheads." The
extended model is clearly superior to alternatives on statistical grounds.
We then analyze the economic implications of this more powerful model. We analyze the
predictions of the model for the valuation and pricing of mortgage pools and mortgage-backed
securities. Based upon an extensive Monte Carlo simulation, we find that the ECML model yields
prices for seasoned mortgage pools that deviate by 0.3 to almost 3.0 percent from more primitive
estimates.
The results indicate the empirical importance of heterogeneity and the implications of
non-optimizing behavior for the valuation and pricing of mortgages and mortgage-backed
securities.
Research Category