Percentiles of sums of heavy-tailed random variables: beyond the single-loss approximation

A perturbative approach is used to derive approximations of arbitrary order to estimate high percentiles of sums of positive independent random variables that exhibit heavy tails. Closed-form expressions for the successive approximations are obtained both when the number of terms in the sum is deterministic and when it is random. The zeroth order approximation is the percentile of the maximum term in the sum. Higher orders in the perturbative series involve the right-truncated moments of the individual random variables that appear in the sum. These censored moments are always finite. As a result, and in contrast to previous approximations proposed in the literature, the perturbative series has the same form regardless of whether these random variables have a finite mean or not. For high percentiles, and specially for heavier tails, the quality of the estimate improves as more terms are included in the series, up to a certain order. Beyond that order the convergence of the series deteriorates. Nevertheless, the approximations obtained by truncating the perturbative series at intermediate orders are remarkably accurate for a variety of distributions in a wide range of parameters.     

Urban poverty and labor market dynamics in five Latin American countries: 2003–2008

Latin America experienced a long period of sustained growth since 2003 that positively impacted social and labor market indicators, including poverty. This paper contributes to the understanding of this process as it carries out a comparative study of poverty dynamics in five Latin American countries during 2003–2008. It analyzes the extent to which countries with different levels of poverty incidence diverge in terms of poverty exit and entry rates, identifies the relative importance of the frequency and impact of events associated to poverty transitions and examines how these events affect households with different characteristics. For this, a dynamic analysis of panel data is carried out using regular household surveys. Sizeable rates of poverty movements were observed in all five countries and it was found that a large proportion of household experienced positive events, mainly related to the labor market; however, only a small fraction of them actually exited poverty. Demographic events and public cash transfers proved to be of little relevance; in particular, the latter did not contribute much either to intensify poverty exits or to prevent poverty entries. Households with children experienced more (less) negative (positive) events than those without children. It appeared therefore that even when the economy behaved reasonably well at the aggregate level, high levels of labor turnover and income mobility (even of a negative nature) still prevail, mainly associated to the high level of precariousness and the undeveloped system of social protection that characterize the studied countries.     

Measuring is Believing! Improving Conventional Indicators of Welfare State Development

Welfare effort (social spending as a percentage of GDP) has conventionally been the preferred measure for comparisons in space and time of the level of development of welfare states. However, a wide variety of other measuring systems are potentially available in this field, because there are different sources and different methods for calculating social spending, so a variety of indicators can be calculated, each of which best reflects a different aspect of social protection systems. This paper presents two innovations: first it proposes options other than those generally used to measure the relative development of welfare states. Secondly, it uses those new measurements to show that some widely accepted conclusions on the relative development of welfare states need to be reviewed.     

Forced Migration,Climate Change,Mitigation and Adaptive Policies in Mexico: Some Functional Relationships

Natural disasters related to hydro-meteorological events have increased during the last few decades, both in frequency and severity. Mexico is heavily exposed to climate change, but has also suffered in the past from climate variability ( Blümel, 2009 ). The new risks oblige the government to develop mitigation processes, while the affected people are implementing strategies of adaptation and resilience-building, mostly at the family and community level. This includes forced migration due to climate change into the slums of megacities or illegal immigration to the United States. The arid, semi-arid and subhumid condition of 49.2 per cent of the territory of Mexico is seriously affected by climate change. In addition, poverty and the lack of jobs have created complex livelihood situations, in which young people leave rural areas, partly due to socio-economic pull factors. In this paper, we address the functional relationships between climate patterns and migration processes in Mexico, highlighting the linkages between the origin of migrants, their economic activity and their vulnerability to extreme events and we discuss long-term climate patterns. Agriculture still uses 78 per cent of the available water in Mexico. In the drylands the competition for water use requires an integrated policy to deal with the new threats from climate change, including mitigation from the top down and adaptation processes from the bottom up to reduce the social vulnerability of the rural population in the highly affected drylands of the central and northern parts of Mexico. The new policy for administering water resources, which promotes the efficient use of an increasingly scarce and polluted resource, still suffers from a lack of participation by the affected rural population. In this paper, we propose an integrated management system from the watershed onwards, involving socio-economic, political, cultural and hydrological variables, to deal with the rising scarcity of water, and the uncertainty and complexity of climate change.     

Resource Constraints or Cultural Conformity? Nonprofit Relationships with Businesses

Nonprofit interactions with businesses have become increasingly diverse, but which nonprofits establish relationships, and to what extent do relationships depend on the form or type of tie? Focusing on nonprofit collaboration with businesses and donations from businesses, we test arguments based on sociological institutionalism and resource dependence theory. We find that nonprofits relying on earned income, nonprofits led by individuals with management degrees, and rationalized nonprofits all are more likely to report collaborations with businesses, aligning with expectations from institutional theory. For donative ties between businesses and nonprofits, we find that rationalized nonprofits are more likely to have charitable gifts from businesses. However, nonprofits with earned income are less likely to have business donations, and funding diversity has a salient positive effect. These results reveal important but paradoxical institutional and resource dependence effects. We conclude with a discussion of our divergent findings and set an agenda for additional research on the topic.     

Model Selection Using Conditional Densities

In this article we propose a new method to select a discrete model f(x; θ), based on the conditional density of a sample given the value of a sufficient statistic for θ. The main idea is to work with a broad family of discrete distributions, called the family of power series distribution, for which there is a common sufficient statistic for the parameter of interest. The proposed method uses the maximum conditional density in order to select the best model.

We compare our proposal with the usual methodology based on Bayes factors. We provide several examples that show that our proposal works fine in most instances. Bayes factors are strongly dependent on the prior information about the parameters. Since our method does not require the specification of a prior distribution, it provides a useful alternative to Bayes factors.     

Divergent pathways: the road to higher education for second-generation Turks in Austria

The article aims to explore immigrant educational pathways in relation to access to higher education (HE) in the Austrian context. Specifically focusing on Turkish youth, the author presents case studies of students who successfully entered HE in spite of their disadvantaged social, ethnic and geographic background. By further enhancing Ball’s distinction (Ball, Reay, and David 2002) between embedded and contingent choosers, the article provides an in-depth understanding of the cultural and structural context in which these students’ educational choices are played out. Finally, reaching out for Turner’s (1960 Turner, R. H. 1960. “Sponsored and Contest Mobility and the School System.” American Sociological Review 25 (6): 855–867.10.2307/2089982[Crossref], [Web of Science ®] , [Google Scholar]) notion of sponsored mobility, the article reflects on how the process of early selection reduces the opportunities for immigrant youth to access seemingly open and free HE.