This paper uses new data from the PSID to quantify the relative importance of negative equity versus ability to pay, in driving mortgage defaults between 2009 and 2013. These data allow us to construct household budgets sets that provide better measures of ability to pay. Changes in ability to pay have large estimated effects. Job loss has an equivalent effect on the propensity to default as a 35% decline in equity. Strategic motives are also found to be quantitatively important, as we estimate more than 38% of households in default could make their mortgage payments without reducing consumption.

To what extent is a worker's human capital growth affected by the quality of his coworkers? To answer this question, we develop and estimate a model in which the productivity and the human capital growth of an individual depend on the average human capital of his coworkers. The measured production function is supermodular: The marginal product of a more knowledgeable individual is increasing in the human capital of his coworkers. The measured human capital accumulation function is convex: An individual's human capital growth is increasing in coworkers' human capital only when paired with more knowledgeable coworkers, but independent of coworkers' human capital when paired with less knowledgeable coworkers. Learning from coworkers accounts for two thirds of the stock of human capital accumulated on the job. Technological changes that increase production supermodularity lead to labor market segregation and, by reducing the opportunities for low human capital workers to learn from better coworkers, lead to a decline in aggregate human capital and output.