Stochastic Measures of Network Resilience: Applications to Waterway Commodity Flows

Given the ubiquitous nature of infrastructure networks in today's society, there is a global need to understand, quantify, and plan for the resilience of these networks to disruptions. This work defines network resilience along dimensions of reliability, vulnerability, survivability, and recoverability, and quantifies network resilience as a function of component and network performance. The treatment of vulnerability and recoverability as random variables leads to stochastic measures of resilience, including time to total system restoration, time to full system service resilience, and time to a specific α% resilience. Ultimately, a means to optimize network resilience strategies is discussed, primarily through an adaption of the Copeland Score for nonparametric stochastic ranking. The measures of resilience and optimization techniques are applied to inland waterway networks, an important mode in the larger multimodal transportation network upon which we rely for the flow of commodities. We provide a case study analyzing and planning for the resilience of commodity flows along the Mississippi River Navigation System to illustrate the usefulness of the proposed metrics.     

Stages and modes of incorporation of exiles in Switzerland: The example of Chilean refugees

Many scholars perceive the incorporation of refugees and immigrants to a new society as a matter of time: the longer the length of residence, the more the refugees and immigrants perceive their stay in the host society as permanent. Other social scientists go even much further: they perceive adaptation not only as a linear process but also as an inevitable and desirable process which should lead to the disappearance of immigrants as an ethnic community and to their assimilation to a new society. In this paper we argue that incorporation to a new society is not necessarily a linear process depending exclusively upon length of residence. We also argue that assimilation is not necessarily the end result of this process. In our opinion, linear and assimilationist approaches neglect macro‐social context and, to a lesser extent, social stratification which are important variables influencing the incorporation process of migrants to a new society. The empirical study of Chilean refugees in Switzerland shows the relevance of these factors and also of the actor's own perception of the situation in the definition of different stages of exile.     

The relationship between job insecurity and accident under-reporting: A test in two countries

Although the problem of accident under-reporting is increasingly recognized in the literature, less is known regarding work environment variables that predict the severity of such under-reporting. Data on perceived job insecurity and on the numbers of both accidents that were experienced and accidents that were actually reported over a period of one year were obtained from 786 employees in 24 US organizations and 563 employees in 20 Italian organizations in sectors where safety is highly relevant. Analysis of these data suggested that not only is job insecurity related to the likelihood of experiencing an accident, but also perceptions of job insecurity may serve to inhibit the reporting of accidents to appropriate company officials. Overall, the rate of accidents was lower in Italy than the United States. Moreover, in both countries, when job insecurity was low, there was little difference between the total number of experienced accidents and the number that employees reported. However, as job insecurity increased, the under-reporting of accidents increased. The implications of these results are discussed in light of the globally increasing prevalence of job insecurity in today's workplace.     

A test of concordance based on Gini’s mean difference

A new rank correlation index, which can be used to measure the extent of concordance or discordance between two rankings, is proposed. This index is based on Gini’s mean difference computed on the totals ranks corresponding to each unit and it turns out to be a special case of a more general measure of the agreement of m rankings. The proposed index can be used in a test for the independence of two criteria used to rank the units of a sample, against their concordance/discordance. It can then be regarded as a competitor of other classical methods, such as Kendall’s tau. The exact distribution of the proposed test-statistic under the null hypothesis of independence is studied and its expectation and variance are determined; moreover, the asymptotic distribution of the test-statistic is derived. Finally, the implementation of the proposed test and its performance are discussed. Both the authors contributed equally to this work; however, the actual writing of the paper was as follows: Sects. 2 and 3 are due to C. G. Borroni, Sects. 1 and 4 are due to M. Zenga.     

A monte carlo analysis of two spectral tests of the martingale hypothesis

Summary The size, power, and robustness properties of the Kolmogorov-Smirnov and Cramér-von Mises spectral tests of the martingale (difference) hypothesis are investigated by Monte Carlo methods. The results highlight a marked superiority of the Cramér-von Mises with respect to the Kolmogorov-Smirnov test. The paper also shows that the Cramér-von Mises test is simple to compute, more general and more powerful than other converntionally used tests.     

A Monte Carlo EM algorithm for random-coefficient-based dropout models

Longitudinal studies of neurological disorders suffer almost inevitably from non-compliance, which is likely to be non-ignorable. It is important in these cases to model the response variable and the dropout mechanism jointly. In this article we propose a Monte Carlo version of the EM algorithm that can be used to fit random-coefficient-based dropout models. A linear mixed model is assumed for the response variable and a discrete-time proportional hazards model for the dropout mechanism; these share a common set of random coefficients. The ideas are illustrated using data from a five-year trial assessing the efficacy of two drugs in the treatment of patients in the early stages of Parkinson's disease.     

DOES IDIOSYNCRATIC BUSINESS RISK MATTER FOR GROWTH?

Several imperfections can prevent entrepreneurs from diversifying away the idiosyncratic risk of their business. As a result idiosyncratic risk discourages entrepreneurial activity and hinders growth, with the effects being stronger in economies with lower risk diversification opportunities. In accordance with this prediction, we find that OECD countries with low levels of risk diversification opportunities (as measured by the relevance of family firms or of widely held companies) perform relatively worse (in terms of productivity, investment, and business creation) in sectors characterized by high idiosyncratic risk. Differently from previous literature, we allow risk to be country specific. Since risk is endogenous to risk diversification opportunities, we instrument its value using sectoral risk in the United States, a country where idiosyncratic business risk can be more easily diversified away. Tackling the endogeneity of risk and recognizing that it varies by country magnifies the estimated effects of risk on growth.     

The extraordinary claim of praxeology

The author states first praxeology's dilemma: if its theoremes are a priori in the unidimensional sense in which praxeology seems to be intended, then the theory as represented in the theorem is inapplicable. If it is not a priori in that sense, then praxeology is already defeated. In a concrete analysis of a part of a praxeological system the author shows that the contention which sees economic theory simply as the result of formal deduction starting from an a priori axiom is unfounded. As a language, praxeology is not water-tight; its line of reasoning must always draw from the inarticulate background of professional knowledge. Praxeology can be explained away as a process of dialectical redefinition of concepts, ultimately and inevitably dependent upon empirical hypotheses.     

Risk aversion,downside risk aversion,and the transition to entrepreneurship

In this paper, we discuss the transition from secure employment to risky self-employment (entrepreneurship) caused by a small increase in wealth. Building on the apportioning risk literature, we prove that the transition from secure employment to risky entrepreneurship is based on a measure of the difference between the strength of downside risk aversion and the strength of risk aversion. This result highlights the idea that using the behavioral approach of risky lotteries to study entrepreneurship can produce different results from the traditional economic theory of entrepreneurship, which can have policy implications that must be considered with caution.