Inference on Breakdown Frontiers

Given a set of baseline assumptions, a breakdown frontier is the boundary between the set of assumptions which lead to a specific conclusion and those which do not. In a potential outcomes model with a binary treatment, we consider two conclusions: First, that ATE is at least a specific value (e.g., nonnegative) and second that the proportion of units who benefit from treatment is at least a specific value (e.g., at least 50\%). For these conclusions, we derive the breakdown frontier for two kinds of assumptions: one which indexes relaxations of the baseline random assignment of treatment assumption, and one which indexes relaxations of the baseline rank invariance assumption. These classes of assumptions nest both the point identifying assumptions of random assignment and rank invariance and the opposite end of no constraints on treatment selection or the dependence structure between potential outcomes. This frontier provides a quantitative measure of robustness of conclusions to relaxations of the baseline point identifying assumptions. We derive $\sqrt{N}$-consistent sample analog estimators for these frontiers. We then provide two asymptotically valid bootstrap procedures for constructing lower uniform confidence bands for the breakdown frontier. As a measure of robustness, estimated breakdown frontiers and their corresponding confidence bands can be presented alongside traditional point estimates and confidence intervals obtained under point identifying assumptions. We illustrate this approach in an empirical application to the effect of child soldiering on wages. We find that sufficiently weak conclusions are robust to simultaneous failures of rank invariance and random assignment, while some stronger conclusions are fairly robust to failures of rank invariance but not necessarily to relaxations of random assignment.Comment: 65 pages. 26 page supplemental appendi

Third Party Support and Risk Costs in Supply Chain Coordination

It is broadly accepted that supply chain members which can jointly optimize their decisions, using techniques such as joint economic lot-sizing (JELS), will always produce equal or superior total profits than those supply chains which do not cooperate. In addition to increased profits, cooperation offers other established benefits. The majority of research has explored the use of coordination mechanisms (e.g. quantity discounts) to improve on purely competitive (arms-length) arrangements in supply chain purchase contracts. Though the use of these mechanisms can potentially improve profits, they often fail to offer any substantive guidance in implementing the proposed solution. Further, the JELS solution proposals often presuppose a spontaneous and effective coordination effort led by one or both supply chain parties. However, research has shown that very little meaningful cooperation occurs in practice. This thesis proposes and explores the novel use of an expert third party to assist in coordination and cooperation efforts of a contract-based dyadic (supplier-buyer) relationship. It is shown that coordination using a third party can, not only ensure optimal profits for the entire supply chain, but also provide significant contributions to the extant body of knowledge. These benefits include consideration of intangible factors such as neutral arbitration and protection of confidential information. An updated cost model accounts for many costs not typically considered in lot-sizing problems, including the introduction of the seller's costs of commitment and contract costs. Numerical studies via simulation are performed to add insight into the implications of the updated model. Sensitivity and algebraic analyses are included for selected scenarios.Ph.D., Finance -- Drexel University, 201

On Resilient Behaviors in Computational Systems and Environments

The present article introduces a reference framework for discussing resilience of computational systems. Rather than a property that may or may not be exhibited by a system, resilience is interpreted here as the emerging result of a dynamic process. Said process represents the dynamic interplay between the behaviors exercised by a system and those of the environment it is set to operate in. As a result of this interpretation, coherent definitions of several aspects of resilience can be derived and proposed, including elasticity, change tolerance, and antifragility. Definitions are also provided for measures of the risk of unresilience as well as for the optimal match of a given resilient design with respect to the current environmental conditions. Finally, a resilience strategy based on our model is exemplified through a simple scenario.Comment: The final publication is available at Springer via http://dx.doi.org/10.1007/s40860-015-0002-6 The paper considerably extends the results of two conference papers that are available at http://ow.ly/KWfkj and http://ow.ly/KWfgO. Text and formalism in those papers has been used or adapted in the herewith submitted pape

Connecting in the Kitchen:An Empirical Study of Physical Interactions while Cooking Together at Home

Recent research has explored the role technology might play in future kitchens, including virtually dining together, recipe sharing, augmented kitchen furniture, reactive cooking utensils and gestural interaction. When people come together in a kitchen to cook it is about more than just production of sustenance – it is about being together, helping each other, exchanging stories, and contributing to the gradual emergence of a shared meal. In this paper we present a digital ethnography of how people coordinate and cooperate in their kitchens when cooking together for the purpose of inspiring the design of social natural user interactions for technologies in the kitchen. The study is based on 61 YouTube videos of people cooking together analyzed using the frameworks of proxemics and F-formations. Our findings unfold and illustrate relationships between people’s spatial organization, their cooking activities and physical kitchen layouts. Based on these we discuss the kitchen as a design space and particularly the opportunities for social natural user interaction design. Author Keywords F-formations; proxemics; natural user interaction; cooking together; digital ethnography; digital kitchens; the home ACM Classification Keywords H5.3 Computer-supported cooperative wor

Adolescent Propensity to Engage in Health Risky Behaviors: The Role of Individual Resilience

In this paper we create indices of resilience to identify adolescents at risk of smoking, drinking alcohol, and using illegal drugs. Using data from the National Longitudinal Study of Adolescent Health, three manifestations of resilience were identified: overall-resilience, self/family-resilience, and self-resilience. Our analysis reveals that the overall-resilient were less likely to engage in risky behaviors. The self/family resilient were more likely to engage in risky behaviors, but consumed less. The self-resilient had reduced risk for smoking and drinking alcohol but elevated risk for using illegal drugs and being in an addictive stage of smoking and drinking, if participating