This dissertation consists of two parts. Part one deals with the concerns that the largest federal nutrition program, the Food Stamp Program (FSP), may have caused low-income women to be obese. Part two studies the trend of agricultural labor migration and estimates the effects of migration on wages.

The first essay of the dissertation, entitled "Do Food Stamps Contribute to Obesity in Low-Income Women?" estimates the effects of food stamps on obesity, overweight and body mass index (BMI) of low-income women. This question is particularly important because participants are substantially more likely to be obese than are nonparticipants. Our analysis differs from previous research in three aspects. First, we exploit a rich longitudinal data set, the National Longitudinal Survey of Youth 1979 (NLSY79), to distinguish between full-time and part-time participation. Second, instead of making parametric assumptions on outcomes, we employ a variety of difference-in-difference matching estimators to control for selection bias. Third, we estimate both short-term (one year of participation) and long-term (three years of participation) treatment effects. Empirical results show that, after controlling for selection bias and defining the treatment and comparison groups carefully, there is little evidence that food stamps are responsible for obesity or higher BMI in female participants. Our estimates are robust to different definitions of the treatment and comparison groups and to various matching algorithms. We further examine prior studies and apply their methods to our samples. We repeat analyses of previous studies using our sample and find that prior studies significantly overstate the causal relationship between the FSP and obesity.

The second essay of the dissertation, entitled "Migrant Workers in U.S. Agricultural Labor Market," studies an unprecedented sharp decrease of migrant workers on U.S. crop farms. We find that who migrates within the U.S. agricultural labor market depends largely on individuals' demographic characteristics. Shifts in the distribution of these characteristics and the response to the September 11 terrorist attacks are largely responsible for the sharp decline in the fraction of agricultural migrant workers from 55 percent in 1998 to 24 percent in 2006.

The third essay of the dissertation, entitled "Mobility and Wages in U.S. Agricultural Labor Market," studies the mobility of agricultural workers and wages in the agricultural labor market. We employ the National Agricultural Workers Survey (NAWS) to (1) examine migration and individual wages, (2) test the hypothesis of the dual labor market theory, and (3) estimate the effect of migration on local wage dispersion. Our empirical results suggest that the dual labor market considerations play a larger role in explaining why agricultural workers migrate than do expected wage differentials. We also find that the decrease in labor migration leads to greater wage dispersion within local agricultural labor market.