林明仁 Ming-Jen Lin​

Using national data of the male population (a total of 715,000 observations) in Taiwan, this study finds a significant association between LBW and the probability of committing crime appears exclusively among those born to mothers under 18 or over 40 at the time of childbearing. Moreover, this association occurs particularly in violent crime. The interaction between biological and demographic factors suggests that being born to very old or young mothers and LBW together may create a double hazard of biological disadvantage, leading to higher risk of committing violent crime later. The other side of the coin is that, regarding to violent crime, being born low birth weight may not be a disadvantage unless it is triggered by certain adversity.

By combining two unique Taiwanese datasets, this paper investigates how birth weight affects grades at age 15 years. To tackle the endogeneity problem caused by omitted variables, we first compare birth weight and grade variation within twins. We find that birth weight does increase grades but only when both twins weigh less than 3000g at birth, which indicates that the effect is non-linear, and when the weight difference between the twins is larger than 200g. Furthermore, twin fixed effect estimates are similar to the ordinary least squares (OLSs) ones. We then use the public health budget and the number of doctors in the county where the children were born as instrumental variables for the children's birth weight. We found that instrumental variable estimates are significant only for the less educated (<9 years) and young (<25 years) mothers. We conclude that the effect of birth weight is real and non-linear and its effect on less educated and young mothers is the most severe. Furthermore, the bias produced by OLS may not be large if the correct subgroup of the population has been identified.

Economic theory suggests police and crime are negatively correlated. However, it is surprisingly difficult to demonstrate this relation empirically, as areas with greater numbers of crimes tend to hire more police. In order to resolve this simultaneity, we begin by exploring the structure of the financial relationship existing between state and local governments, arguing that variations in state tax rates can serve as an instrumental variable for local police numbers. Two-stage least square (2SLS) result show that the elasticity of police presence with respect to crime is about −1.1 for violent crime, and −0.9 for property crime. These results are mostly significant, and are more negative than those obtained under OLS. Overall, our estimations suggest that police does reduce crime.

The "missing women" phenomenon in many Asian countries has previously been regarded as the result of son preference. However, some studies have argued half of the missing women can be explained by infection with Hepatitis B virus (HBV). We demonstrate that the probability of having a male birth is only slightly higher for HBV mothers than for mothers without HBV. The sex ratio at birth rises for the higher birth order and that in families where the first two children are female. Our findings suggest that HBV status has little impact on the missing women phenomenon.

OLS may understate the effect of unemployment on crime because of the endogeneity problem (Raphael and Winter-Ember 2001). In this paper, we use changes in the real exchange rate, state manufacturing sector percentages, and state union membership rates as novel instrumental variables to carry out 2SLS estimations. We find a one-percentage-point increase in unemployment would increase property crime by 1.8 percent under the OLS method, but that the elasticity goes up to 4 percent under 2SLS. The larger 2SLS effect has significant policy implications because it explains 30 percent of the property crime change during the 1990s.