"This dissertation considers two distinct issues in macroeconomics. The first and second chapters look at the effects of changes in tax policy on productivity of an economy from an empirical and theoretical stand point. The third chapter concerns the implications of cross-national migration for long-run growth and welfare. In the first chapter, I analyze the effects of tax policy changes on US total factor productivity (TFP). A substantial fraction of the income differences between countries can be explained by differences in TFP. Thus it is important to know the effects of policy changes on TFP. This is the first study that looks at the effect of changes in tax policy on TFP. Data on tax shocks comes from the sources used by Romer and Romer (2009). Empirical estimates show that a 1 percent permanent exogenous rise in total taxes lowers TFP by up to 1.75 percent in the long run. The drop in output associated with the increase in taxes is between 2 and 3 percent. Thus the change in TFP explains most of the movement in output that follows a tax change. Individual income taxes have a strong and significant effect on TFP whereas corporate income taxes do not significantly affect TFP or most other macroeconomic variables. The analysis also shows that the effects of tax changes on output and on observable inputs have become smaller over time while the effects on TFP and on wages have become larger over time. In the second chapter, I build a dynamic stochastic general equilibrium model to explain the dynamic macroeconomic effects of tax changes. The model has two key features: learning-by-doing at the worker level and endogenous TFP evolution whereby TFP growth depends on investment and human capital. When I calibrate the learning-by-doing and TFP evolution processes using micro evidence on the effect of human capital accumulation on productivity, the effect of taxes on TFP in the model is substantially less elastic than in the data. When I instead select parameters to match key aggregate moments, the estimated model is successful in accounting for the qualitative and quantitative nature of the empirical results. However, this requires stronger learning-by-doing than seems reasonable given the microeconomic evidence. I argue that the gap between the model and data may arise because some of the tax changes labeled as exogenous by Romer and Romer (2009) are in fact endogenous in which case the empirical results would overstate the true effects of tax changes on TFP. The difference between model and data may also arise because of the model not being rich enough. The model drives its components from both the business cycle and endogenous growth literature, thus the gap between model and data perhaps shows that the literature is not adequate in explaining observed patterns in the data. The third chapter characterizes the effect of the much-discussed 'brain drain' - the migration of relatively skilled workers from less to more advanced economies - on long-run development in the workers' home nation. A summary of the model is as follows: I employ a life cycle model with two countries, one poor and one rich, with endogenous migration and return migration decisions from and to the poor country. Workers working in the poor country receive wage offers from the rich country and decide to migrate to the rich country if the wage offer and subsequent wage growth gives them a higher lifetime utility than from staying in the poor country. The workers who migrate to the rich country have higher wage and skill growth rates than the workers in poor. The central question of this chapter is to evaluate the costs and benefits of a policy where the government of the poor country incentivizes the expatriates to return from the rich country to the poor country to take advantage of their superior skills that they accumulate while working in the rich country. The direct benefit from calling back workers from the rich country is the increase in output of the poor country because of the higher skills of return migrants relative to domestic workers. The indirect benefit to the poor country is the increase in skill level of domestic workers because of the positive externalities from the returning workers. However, every worker that is called back to work in the poor country must also be given high enough compensation so that he is indifferent between working in the two countries. This is the cost of bringing a worker back. These costs and benefits determine 1) whether it is beneficial to call expatriates back or not, and 2) which workers benefit the country the most. Results show that the economy can gain the most by calling back workers with skill levels that are 1.28 standard deviations above the mean skill level of domestic workers. In the model, since skill is a combination of education and experience, this skill level in real life can either correspond to highly skilled young professionals or highly experienced professional or a combination of both. Calling back workers of lower skill levels will lower the gain since their experience in the rich country would not be high and hence the superior skill accumulation would be lower. Calling back workers of higher skill levels will lower the gain since the cost of calling them back would be too high"--Page v-vii.

This dissertation presents a series of three essays that examine the functional form of the U.S. federal income tax and its implications. In the first essay we introduce the convex functional form of the income tax which we believe is superior to the standard income-proportional form. We also describe the parameters within this function and their construction over the years from 1913 to 2005. The second essay discusses the characteristics of the time series of these parameters, the relation of these series to other tax series in the literature, the relation of the intertemporal variation in the tax parameters to the sharp reduction in volatility of macroeconomic time series after about 1950, and the interrelation of the tax parameters with other federal fiscal variables. In chapter three, we use a standard dynamic stochastic general equilibrium model and insert our tax function. We explore the implications that different tax policies will have on the macroeconomy by changing parameter values within this tax function. Specifically we compare the steady states values, second moments, and impulse response functions, of the usual variables, generated by these policies.

This thesis is a collection of three papers in macroeconomics and public finance. It develops Dynamic Stochastic General Equilibrium Models with a special focus on financial frictions to analyze the effects of changes in corporate tax policy on firm level and macroeconomic aggregates. Chapter 1 develops a dynamic general equilibrium model with a representative firm to assess the short-run effects of changes in the timing of corporate profit taxes. First, it extends the Ricardian equivalence result to an environment with production and establishes that a temporary corporate profit tax cut financed by future tax-increase has no real effect when the tax is lump sum and capital markets are perfect. Second, I assess how strong the ricardian forces are in the presence of financing frictions. I find that when equity issuance is costly, and when the firm faces a lower bound on dividend payments, a temporary tax cut reduces temporary the marginal cost of investment and implies positive marginal propensity of investment. Third, I analyze how do the intertemporal substitution effects of tax cuts interact with the stimulative effects when tax is not lump-sum. The results show that when tax is proportional to corporate profit, the expectations of high future tax rates reduce the expected marginal return on investment and mitigate the stimulative effects of tax cuts. The net investment response depends on the relative strength of each effect. Chapter 2 is co-authored with Rui Castro. In this paper, we quantify how effective temporary corporate tax cuts are in stimulating investment and output via relaxation of financing frictions. In fact, policymakers often rely on temporary corporate tax cuts in order to provide incentives for business investment in recession times. A common motivation is that such policies help relax financing frictions, which might bind more during recessions. We assess whether this mechanism is effective. In an industry equilibrium model where some firms are financially constrained, marginal propensities to invest are high. We consider a transitory corporate tax cut, funded by public debt. By increasing current cash flows, corporate tax cuts are effective at stimulating current investment. On impact, aggregate investment increases by 26 cents per dollar of tax stimulus, and aggregate output by 3.5 cents. The stimulative output effects are long-lived, extending past the period the policy is reversed, leading to a cumulative effect multiplier on output of 7.2 cents. A major factor preventing larger effects is that this policy tends to significantly crowd out investment among the larger, unconstrained firms. Chapter 3 studies the effects of the 1992's U.S. Treasury Department proposal of a Comprehensive Business Income Tax (CBIT) reform. According to the U.S. tax code, dividend and capital gain are taxed at the firm level and further taxed when distributed to shareholders. This double taxation may reduce the overall return on investment and induce inefficient capital allocation. Therefore, tax reforms have been at the center of numerous debates among economists and policymakers. As part of this debate, the U.S. Department of Treasury proposed in 1992 to abolish dividend and capital gain taxes, and to use a Comprehensive Business Income Tax (CBIT) to levy tax on corporate income. In this paper, I use an industry equilibrium model where firms are subject to financing frictions, and idiosyncratic productivity and entry/exit shocks to assess the long run effects of the CBIT. I find that the elimination of the capital gain and dividend taxes is not self financing. More precisely, the corporate profit tax rate should be increased from 34\% to 42\% to keep the reform revenue-neutral. Overall, the results show that the CBIT reform reduces capital accumulation and output by 8\% and 1\%, respectively. However, it improves capital allocation by 20\%, resulting in an increase in aggregate productivity by 1.41\% and in a modest welfare gain.

This thesis addresses interactions between monetary and fiscal policies in a theoretical dynamic stochastic general equilibrium (DSGE) model of a small open economy and in an empirical model under a structural vector error correction model (SVECM). The thesis consists of three essays. The contribution is both theoretical and empirical that enables a better understanding of the complexity of interactions between monetary and fiscal policies in small open economies. The first essay examines the equilibrium determinacy under monetary and fiscal rules. The goal is to investigate how monetary and fiscal policy interactions ensure a unique and non-explosive (determinate) equilibrium for a small open economy. The study focuses when policy makers implement a set of policy mixes to address domestic output price inflation control for monetary policy, debt stabilization for fiscal policy, and joint output stabilization tasks. The result indicates that two policy schemes facilitate a determinate equilibrium. First, monetary policy actively controls inflation when fiscal policy sets a sufficient feedback on debt. Second, monetary policy becomes passive against inflation when fiscal policy is insolvent. Adding output stabilization to each rule simply causes variants of this fundamental. An interest rate rule with output stabilization can be more passive against inflation while providing a stronger response to the output gap. Fiscal policy is required to set higher feedback on debt along with its stronger counter-cyclical policy. The second essay links between the equilibrium determinacy and policy optimization. This essay provides insights into the design of policy mixes and compares determinacy outcomes between two theoretical models of a small open economy: with and without an explicit exchange rate role. This study shows that policy interactions in a small open economy with an endogenous exchange rate is quite sophisticated, especially when a monetary rule is added with an output stabilization task and/or targeted to Consumer Price Index (CPI) inflation. Additional concern for monetary policy in an open economy causes a partial offset to its reaction on domestic output price inflation that weakens its effect on the real debt burden. To minimize economic fluctuations, policy makers should mute the role of output stabilization for monetary policy, and set minimum feedback on debt that is compatible with the degree of counter-cyclical fiscal policy. Substantially active response to inflation is satisfactory for monetary policy with CPI inflation targeting. The third essay empirically presents monetary and fiscal policy interactions in Thailand's SVECM suggested by a theoretical DSGE model developed from the previous essays. This essay shows that the DSGE-SVECM model can be supported by Thai data. A shock to monetary policy is effective with a lag. Government spending policy is also effective with a lag and some crowding-out effects on output. An adverse shock in tax policy unexpectedly stimulates the economy, indicating room for enhancing economic growth by relaxing revenue constraint. Monetary policy is mainly implemented to correct a consequence of a fiscal shock on inflation (and also the domestic and foreign shocks), while fiscal policy appears to counter a consequence of the monetary policy shock on output.