AbstractWe study the incentives to improve ability in a model where heterogeneous firms and workers interact in a labor market characterized by matching frictions and costly screening. When effort in improving ability raises both the mean and the variance of the resulting ability distribution, multiple equilibria may arise. In the high-effort equilibrium, heterogeneity in ability is sufficiently large to induce
firms to select the best workers, thereby confirming the belief that effort is important for finding good jobs. In the low-effort equilibrium, ability is not sufficiently dispersed to justify screening, thereby con
firming the belief that effort is not so important. The model has implications for wage inequality, the distribution of firm characteristics, sorting patterns between
firms and workers, and unemployment rates that can help explaining inter- national variation in socio-economic and labor market outcomes.