Addressing the Zeros Problem: Regression Models for Outcomes with a Large Proportion of Zeros, with an Application to Trial Outcomes

In law‐related and other social science contexts, researchers need to account for data with an excess number of zeros. In addition, dollar damages in legal cases also often are skewed. This article reviews various strategies for dealing with this data type. Tobit models are often applied to deal with the excess number of zeros, but these are more appropriate in cases of true censoring (e.g., when all negative values are recorded as zeros) and less appropriate when zeros are in fact often observed as the amount awarded. Heckman selection models are another methodology that is applied in this setting, yet they were developed for potential outcomes rather than actual ones. Two‐part models account for actual outcomes and avoid the collinearity problems that often attend selection models. A two‐part hierarchical model is developed here that accounts for both the skewed, zero‐inflated nature of damages data and the fact that punitive damage awards may be correlated within case type, jurisdiction, or time. Inference is conducted using a Markov chain Monte Carlo sampling scheme. Tobit models, selection models, and two‐part models are fit to two punitive damage awards data sets and the results are compared. We illustrate that the nonsignificance of coefficients in a selection model can be a consequence of collinearity, whereas that does not occur with two‐part models

Do Trustees and Administrators Matter? Diversifying the Faculty Across Gender Lines

Our paper focuses on the role that the gender composition of the leaders of American colleges and universities – trustees, presidents/chancellors, and provosts/academic vice presidents – plays in influencing the rate at which academic institutions diversify their faculty across gender lines. Our analyses make use of institutional level panel data that we have collected for a large sample of American academic institutions. We find, other factors held constant including our estimate of the “expected” share of new hires that should be female, that institutions with female presidents/chancellors and female provosts/academic vice presidents, as well as those with a greater share of female trustees, increase their shares of female faculty at a more rapid rate. The magnitudes of the effects of these leaders are larger at smaller institutions, where central administrators may play a larger role in faculty hiring decisions. A critical share of female trustees must be reached before the gender composition of the board matters

Optimization and resilience of complex supply-demand networks

Acknowledgments This work was supported by NSF under Grant No. 1441352. SPZ and ZGH were supported by NSF of China under Grants No. 11135001 and No. 11275003. ZGH thanks Prof Liang Huang and Xin-Jian Xu for helpful discussions.Peer reviewedPublisher PD

The Hyperon-Nucleon Interaction Potential in the Bound State Soliton Model: The ΛN\Lambda N Case

We develop the formalism to study the hyperon-nucleon interaction potential within the bound state approach to the SU(3) Skyrme model. The general framework is illustrated by applying it to the diagonal $\Lambda N$ potential. The central, spin-spin and tensor components of this interaction are obtained and compared with those derived using alternative schemes.Comment: source file, 4 ps figure

Shared sanitation and the prevalence of diarrhea in young children: evidence from 51 countries, 2001-2011.

Shared sanitation is defined as unimproved because of concerns that it creates unsanitary conditions; this policy is being reconsidered. We assessed whether sharing a toilet facility was associated with an increased prevalence of diarrhea among children < 5 years of age. We use data from Demographic and Health Surveys conducted in 51 countries. Crude and adjusted prevalence ratios (PRs) for diarrhea, comparing children from households that used a shared facility with children from households that used a non-shared facility, were estimated for each country and pooled across countries. Unadjusted PRs varied across countries, ranging from 2.15 to 0.65. The pooled PR was 1.09; differences in socioeconomic status explained approximately half of this increased prevalence (adjusted PR = 1.05). Shared sanitation appears to be a risk factor for diarrhea although differences in socioeconomic status are important. The heterogeneity across countries, however, suggests that the social and economic context is an important factor

The socioeconomic impact of in-silico models for implantable medical devices: a conceptual framework

The use of in-silico technologies for implantable medical devices has gained importance in the last decade. From a medical perspective, the term ‘in-silico’ mainly refers to computer simulations of clinical trials based on virtual cohorts. So far, there is a lack of a concept how the impact of in-silico models on socioeconomic factors can be evaluated. As part of the EU-funded project SIMCOR, one objective was to conceptualize the impact of in-silico on implantable medical devices. We applied an iterative process described in Jabareen (2009) to build a conceptual framework based on concepts from a comprehensive literature review and expert interviews from academia, companies, and regulatory bodies. Repeated steps of literature work, exploratory interviews and discussion sessions among the research team led to the final framework that was validated by feedback from experts at the end. The conceptual framework describes the impact from in-silico technologies along the product development cycle of implantable medical devices through impact channels up to socio-economic endpoints referring to firm, market, health system and society. Since the whole conceptual framework has multiple complex impact channels that create a kind of network, each impact channel is explained with its ramifications. One channel reveals that underrepresented patient groups in clinical trials might benefit from in-silico models by enabling to model rarer anatomical configurations and leading to medical device development for a broader range of population. The conceptual framework provides the basis for the quantification of the impacts of in-silico models that is expected to increase the acceptance of these models among different stakeholders. The potential benefits as well as disadvantages can be better estimated and classified from different perspectives. The use of in-silico models is expected to enable access to implantable devices faster and to a larger population group. Key messages • The framework reveals opportunities of in-silico models for different stakeholders, e.g., entrepreneurs, regulators, that might lead to an increased development, use and acceptance of such models. • The framework indicates that in-silico models are expected to accelerate implantable medical device development, increase patient safety, and gain faster access for larger population groups