Weighted and two-stage least squares estimation of semiparametric truncated regression models

This paper provides a root-n consistent, asymptotically normal weighted least squares estimator of the coefficients in a truncated regression model. The distribution of the errors is unknown and permits general forms of unknown heteroskedasticity. Also provided is an instrumental variables based two-stage least squares estimator for this model, which can be used when some regressors are endogenous, mismeasured, or otherwise correlated with the errors. A simulation study indicates that the new estimators perform well in finite samples. Our limiting distribution theory includes a new asymptotic trimming result addressing the boundary bias in first-stage density estimation without knowledge of the support boundary. © 2007 Cambridge University Press.

Multilevel Governance and Accountability: Does Decentralization Promote Good Governance?

Today, the trend towards decentralization is far-reaching. Proponents of decentralization have argued that decentralization promotes responsive and accountable local government by shortening the distance between local representatives and their constituency. However, in this paper, I focus on the countervailing effect of decentralization on the accountability mechanism, arguing that decentralization, which increases the number of actors eligible for policy making and implementation in governance as a whole, may blur lines of responsibility, thus weakening citizens’ ability to sanction government in election. By using the ordinary least squares (OLS) interaction model based on historical panel data for 78 countries in the 2002 – 2010 period, I test the hypothesis that as the number of government tiers increases, there will be a negative interaction between the number of government tiers and decentralization policies. The regression results show empirical evidence that decentralization policies, having a positive impact on governance under a relatively simple form of multilevel governance, have no more statistically significant effects as the complexity of government structure exceeds a certain degree. In particular, this paper found that the presence of intergovernmental meeting with legally binding authority have a negative impact on governance when the complexity of government structure reaches to the highest level.

Food Swamps, Obesity & Health Zoning Restrictions on Fast Food Restaurants

Protecting public health is the most legitimate use of zoning, and yet there is minimal progress in applying it to the obesity problem. Zoning could potentially be used to address both unhealthy and healthy food retailers, but lack of evidence regarding the impact of zoning and public opinion on zoning changes are barriers to implementing zoning restrictions on fast food on a larger scale. My dissertation addresses these gaps in our understanding of health zoning as a policy option for altering built, food environments.

Chapter 1 examines the relationship between food swamps and obesity and whether spatial mapping might be useful in identifying priority geographic areas for zoning interventions. I employ an instrumental variables (IV) strategy to correct for the endogeneity problems associated with food environments, namely that individuals may self-select into certain neighborhoods and may consider food availability in their decision process. I utilize highway exits as a source of exogenous variation .Using secondary data from the USDA Food Environment Atlas, ordinary least squares (OLS) and IV regression models were employed to analyze cross-sectional associations between local food environments and the prevalence of obesity. I find even after controlling for food desert effects, food swamps have a positive, statistically significant effect on adult obesity rates.

Chapter 2 applies theories of message framing and prospect theory to the emerging discussion around health zoning policies targeting food environments and to explore public opinion toward a list of potential zoning restrictions on fast-food restaurants (beyond moratoriums on new establishments). In order to explore causality, I employ an online survey experiment manipulating exposure to vignettes with different message frames about health zoning restrictions with two national samples of adult Americans age 18 and over (N1=2,768 and N2=3,236). The second sample oversamples Black Americans (N=1,000) and individuals with high school as their highest level of education. Respondents were randomly assigned to one of six conditions where they were primed with different message frames about the benefits of zoning restrictions on fast food retailers. Participants were then asked to indicate their support for six zoning policies on a Likert scale. Subjects also answered questions about their food store access, eating behaviors, health status and perceptions of food stores by type.

I find that a message frame about Nutrition and increasing Equity in the food system was particularly effective at increasing support for health zoning policies targeting fast food outlets across policy categories (Conditional, Youth-related, Performance and Incentive) and across racial groups. This finding is consistent with an influential environmental justice scholar’s description of “injustice frames” as effective in mobilizing supporters around environmental issues (Taylor 2000). I extend this rationale to food environment obesity prevention efforts and identify Nutrition combined with Equity frames as an arguably universal campaign strategy for bolstering public support of zoning restrictions on fast food retailers.

Bridging my findings from both Chapters 1 and 2, using food swamps as a spatial metaphor may work to identify priority areas for policy intervention, but only if there is an equitable distribution of resources and mobilization efforts to improve consumer food environments. If the structural forces which ration access to land-use planning persist (arguably including the media as gatekeepers to information and producers of message frames) disparities in obesity are likely to widen.

Nonlinear piezoelectricity in electroelastic energy harvesters: Modeling and experimental identification

We propose and experimentally validate a first-principles based model for the nonlinear piezoelectric response of an electroelastic energy harvester. The analysis herein highlights the importance of modeling inherent piezoelectric nonlinearities that are not limited to higher order elastic effects but also include nonlinear coupling to a power harvesting circuit. Furthermore, a nonlinear damping mechanism is shown to accurately restrict the amplitude and bandwidth of the frequency response. The linear piezoelectric modeling framework widely accepted for theoretical investigations is demonstrated to be a weak presumption for near-resonant excitation amplitudes as low as 0.5 g in a prefabricated bimorph whose oscillation amplitudes remain geometrically linear for the full range of experimental tests performed (never exceeding 0.25% of the cantilever overhang length). Nonlinear coefficients are identified via a nonlinear least-squares optimization algorithm that utilizes an approximate analytic solution obtained by the method of harmonic balance. For lead zirconate titanate (PZT-5H), we obtained a fourth order elastic tensor component of c1111p =-3.6673× 1017 N/m2 and a fourth order electroelastic tensor value of e3111 =1.7212× 108 m/V. © 2010 American Institute of Physics.

The effect of differences in methodology among some recent applications of shearing quotients.

A shearing quotient (SQ) is a way of quantitatively representing the Phase I shearing edges on a molar tooth. Ordinary or phylogenetic least squares regression is fit to data on log molar length (independent variable) and log sum of measured shearing crests (dependent variable). The derived linear equation is used to generate an 'expected' shearing crest length from molar length of included individuals or taxa. Following conversion of all variables to real space, the expected value is subtracted from the observed value for each individual or taxon. The result is then divided by the expected value and multiplied by 100. SQs have long been the metric of choice for assessing dietary adaptations in fossil primates. Not all studies using SQ have used the same tooth position or crests, nor have all computed regression equations using the same approach. Here we focus on re-analyzing the data of one recent study to investigate the magnitude of effects of variation in 1) shearing crest inclusion, and 2) details of the regression setup. We assess the significance of these effects by the degree to which they improve or degrade the association between computed SQs and diet categories. Though altering regression parameters for SQ calculation has a visible effect on plots, numerous iterations of statistical analyses vary surprisingly little in the success of the resulting variables for assigning taxa to dietary preference. This is promising for the comparability of patterns (if not casewise values) in SQ between studies. We suggest that differences in apparent dietary fidelity of recent studies are attributable principally to tooth position examined.