NBER Working Papers by Sun-Bin Kim

This paper assesses biases in policy predictions due to the lack of invariance of "structural'' parameters in representative-agent models. We simulate data under various fiscal policy regimes from a heterogeneous-agents economy with incomplete asset markets and indivisible labor supply. Imperfect aggregation manifests itself through preference shocks in the estimated representative-agent model. Preference and technology parameter estimates are not invariant with respect to policy changes. As a result, the bias in the representative-agent model's policy predictions is large compared to the length of predictive intervals that reflect parameter uncertainty.

We model worker heterogeneity in the rents from being employed in a Diamond-Mortensen-Pissarides model of matching and unemployment. We show that heterogeneity, reflecting differences in match quality and worker assets, reduces the extent of fluctuations in separations and unemployment. We find that the model faces a trade-off--it cannot produce both realistic dispersion in wage growth across workers and realistic cyclical fluctuations in unemployment.

We model unemployment allowing workers to differ by comparative advantage in market work. Workers with comparative advantage are identified by who works more hours when employed. This enables us to test the model by grouping workers based on their long-term wages and hours from panel data. The model captures the greater cyclicality of employment for workers with low comparative advantage. But the model fails to explain the magnitude of countercyclical separations for high-wage workers or the magnitude of procyclical findings for high-hours workers. As a result, it only captures the cyclicality of the extensive, employment margin for low-wage, low-hours workers.

We introduce worker differences in labor supply, reflecting differences in skills and assets, into a model of separations, matching, and unemployment over the business cycle. Separating from employment when unemployment duration is long is particularly costly for workers with high labor supply. This provides a rich set of testable predictions across workers: those with higher labor supply, say due to lower assets, should display more procyclical wages and less countercyclical separations. Consequently, the model predicts that the pool of unemployed will sort toward workers with lower labor supply in a downturn. Because these workers generate lower rents to employers, this discourages vacancy creation and exacerbates the cyclicality of unemployment and unemployment durations. We examine wag...