My dissertation consists of three chapters studying the heterogeneity in the labor market. Chapter 1 studies the by-age employment heterogeneity in response to technology shocks. Chapter 2 studies the by-age labor force participation heterogeneity in response to macroeconomic shocks. Chapter 3 studies the effect of monetary policy on the employment of occupations with different levels of routine task intensity. A central question in macroeconomics is how employment changes in response to technological progress. In Chapter 1, I broaden this question by investigating if there exist age-specific effects. I use the mixed autoregression (MAR) model to explicitly model the employment to population ratio as a function of age. The results show the responses of young and old employment ratios are much more negative than prime-age, and the response of the young is three times lower than that of the old. Moreover, the forecast error variance decomposition results show that technology shocks' contribution decreases by age. The labor force participation rate is weakly procyclical, as opposed to employment, which is strongly procyclical. Therefore, labor force participation is mostly assumed to be constant in the literature. However, the young, prime-age, and old participation rates are heterogeneous in cyclicality and volatility. In Chapter 2, I study the heterogeneity in the participation of 16-65 old in response to important macroeconomic shocks. I extend the identification scheme in the MAR model from zero to sign restrictions, which enable me to include labor market shocks important for explaining participation rate fluctuations. The results show that young, prime-age, and old participation rates respond differently to the technology, demand, labor supply, and wage bargaining shocks.Routine occupation employment share has decreased, while non-routine occupation employment share has increased since the 1980s. This trend of job polarization has been contributing to the growth in wage inequality in the US. In Chapter 3, I study the effect of a contractionary monetary policy shock on occupational employment with different levels of routine task inputs in a MAR model. I show that routine occupation groups' employment, especially those with higher offshorability, are disproportionally affected by a contractionary monetary policy shock.

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.

This dissertation contains several lines of research in macroeconomics and labor economics conducted during the course of my phd. The unifying theme of this research is the study of labor markets that are subject to macro-search frictions and are populated by heterogeneous workers. Combining these features is important for our understanding of the functioning of labor markets, both from a positive and normative standpoint. The first chapter of this dissertation is resolutely on the positive side. It analyzes how the combination of labor market frictions and worker heterogeneity in skills can shed light on the observed fluctuations in entries into and exits out of the labor force. The second chapter is also on the positive ground, but it brings labor market policies to the fore of the analysis. Along with heterogeneity in human capital over the lifecycle, it shows how some policy tools have contributed to the divergent employment experiences of older workers in Europe and in the United States since the 1980s. The third chapter more naturally lends itself to policy implications. It provides a quantitative study of the employment and welfare effects of statutory severance payments in an economy with wealth heterogeneity reflecting the absence of perfect insurance markets faced by risk-averse workers.