How many mortgage defaults resulted from lofty expectations?

A housing bubble is sustained by expectations of further increases in house prices. There is strong suspicion that this is what happened during the US housing boom preceding the last crisis, and that these expectations have triggered excessive mortgage borrowing. Actually verifying that claim is not that straightforward, though, as one needs to find extensive household level data.

Steven Laufer found this for Los Angeles County with panel data that tracks a property and all its mortgages. He comes to the sad conclusion that only 30% of mortgage defaults there were a result of household level shocks. The rest is all about borrowing and mostly extracted additional cash excessively with the expectation that the loan-to-value ratio would be reduced as house prices continue to grow. When this did not materialize, massive defaults resulted. Using the estimation model, Laufer finds that could have been mostly avoided by imposing the 80% loan-to-value ratio. Although this would have lowered house prices by a considerable 14%, this would have reduced defaults by 28%, as small number given the price drop but a large one considering the number of defaults. And house prices in LA are too high anyway.