Improving the EM algorithm for mixtures

One of the estimating equations of the Maximum Likelihood Estimation method, for finite mixtures of the one parameter exponential family, is the first moment equation. This can help considerably in reducing the labor and the cost of calculating the Maximum Likelihood estimates. In this paper it is shown that the EM algorithm can be substantially improved by using this result when applied for mixture models. A short discussion about other methods proposed for the calculation of the Maximum Likelihood estimates are also reported showing that the above findings can help in this direction too.     

Information and Communication Technologies and the Opportunities of Disabled Persons in the Swedish Labour Market

This article attempts to outline the prospects of disabled persons to gain and retain employment within the Information Society by presenting and discussing the results of a labour market policy programme in Sweden based on information technology. The effects of Information and Communication Technologies (ICTs) for unemployed and employed persons with disabilities can be assessed on the micro, as well as on the macro levels. Technological optimism has given rise to expectations about the great potential of ICTs in creating employment opportunities for disabled persons. Technological optimism, however, derives from a deterministic point of view, i.e. ICTs are regarded as an independent variable. This article suggests that ICTs must be regarded as a variable dependent by the economic, social and cultural order. Its effects on disabled persons employment opportunities are not independent by the power relations at a given time.     

Multivariate Poisson regression with covariance structure

In recent years the applications of multivariate Poisson models have increased, mainly because of the gradual increase in computer performance. The multivariate Poisson model used in practice is based on a common covariance term for all the pairs of variables. This is rather restrictive and does not allow for modelling the covariance structure of the data in a flexible way. In this paper we propose inference for a multivariate Poisson model with larger structure, i.e. different covariance for each pair of variables. Maximum likelihood estimation, as well as Bayesian estimation methods are proposed. Both are based on a data augmentation scheme that reflects the multivariate reduction derivation of the joint probability function. In order to enlarge the applicability of the model we allow for covariates in the specification of both the mean and the covariance parameters. Extension to models with complete structure with many multi-way covariance terms is discussed. The method is demonstrated by analyzing a real life data set.     

Generalized linear mixed joint model for longitudinal and survival outcomes

Longitudinal studies often entail categorical outcomes as primary responses. When dropout occurs, non-ignorability is frequently accounted for through shared parameter models (SPMs). In this context, several extensions from Gaussian to non-Gaussian longitudinal processes have been proposed. In this paper, we formulate an approach for non-Gaussian longitudinal outcomes in the framework of joint models. As an extension of SPMs, based on shared latent effects, we assume that the history of the response up to current time may have an influence on the risk of dropout. This history is represented by the current, expected, value of the response. Since the time a subject spends in the study is continuous, we parametrize the dropout process through a proportional hazard model. The resulting model is referred to as Generalized Linear Mixed Joint Model (GLMJM). To estimate model parameters, we adopt a maximum likelihood approach via the EM algorithm. In this context, the maximization of the observed data log-likelihood requires numerical integration over the random effect posterior distribution, which is usually not straightforward; under the assumption of Gaussian random effects, we compare Gauss-Hermite and Pseudo-Adaptive Gaussian quadrature rules. We investigate in a simulation study the behaviour of parameter estimates in the case of Poisson and Binomial longitudinal responses, and apply the GLMJM to a benchmark dataset.     

The labour–nature relationship: varieties of labour environmentalism

ABSTRACT

This special issue is a contribution to environmental labour studies, which aims to investigate the practices and theories that integrate labour and nature, by focusing on labour environmentalism. While nature is privately appropriated and exploited by Capital, workers’ organizations tend to construct nature as labour’s other, a place to enjoy or a place to be protected from destruction at best. In the following introductory article to this special issue, we present our view of what environmental labour studies are investigating and might investigate in the future and the place of labour environmentalism within this broader agenda. We also suggest an analytical framework to evaluate the depth, breadth, and level of the agency of the variations of labour environmentalism. We suggest that environmental labour studies can be a way of studying not only the intersections between social and environmental justice, climate change and working conditions but can also contribute to building a bridge between environmental theory and practice.     

Refugees,migrants, neither,both: categorical fetishism and the politics of bounding in Europe’s ‘migration crisis’

The use of the categories ‘refugee’ and ‘migrant’ to differentiate between those on the move and the legitimacy, or otherwise, of their claims to international protection has featured strongly during Europe’s ‘migration crisis’ and has been used to justify policies of exclusion and containment. Drawing on interviews with 215 people who crossed the Mediterranean to Greece in 2015, our paper challenges this ‘categorical fetishism’, arguing that the dominant categories fail to capture adequately the complex relationship between political, social and economic drivers of migration or their shifting significance for individuals over time and space. As such it builds upon a substantial body of academic literature demonstrating a disjuncture between conceptual and policy categories and the lived experiences of those on the move. However, the paper is also critical of efforts to foreground or privilege ‘refugees’ over ‘migrants’ arguing that this reinforces rather than challenges the dichotomy’s faulty foundations. Rather those concerned about the use of categories to marginalise and exclude should explicitly engage with the politics of bounding, that is to say, the process by which categories are constructed, the purpose they serve and their consequences, in order to denaturalise their use as a mechanism to distinguish, divide and discriminate.     

Regression in a copula model for bivariate count data

In many cases of modeling bivariate count data, the interest lies on studying the association rather than the marginal properties. We form a flexible regression copula-based model where covariates are used not only for the marginal but also for the copula parameters. Since copula measures the association, the use of covariates in its parameters allow for direct modeling of association. A real-data application related to transaction market basket data is used. Our goal is to refine and understand whether the association between the number of purchases of certain product categories depends on particular demographic customers’ characteristics. Such information is important for decision making for marketing purposes.     

New Rage,New Perspectives?

The Eurozone crisis has led to a long and remarkable protest wave. Civil society raised its voice against the ever-harsher austerity measures implemented to deal with the crisis. The article focuses on the role of civil society and its potential to contribute new perspectives to the debate. Such a contribution would depend on two preconditions: 1. Civil society actors need to mobilize successfully to make their voices heard. 2. Civil society actors contribute a perspective that differs to the perspectives of actors from institutionalized politics. Both preconditions are analyzed empirically for two countries that are in very different situations in the crisis scenario: Greece and Germany. Greece has been hit most severely by the crisis; Germany is the most prominent country defining the crisis management, and it provides the largest share of credit guarantees for “crisis countries.” Social movement theory is used to explain the differing evolution of protests in the two countries. In the early phase of the crisis, the established landscape of political parties in both countries offered few opportunities for their citizens to vote in opposition to the crisis management, which is conducive to extra-parliamentary protest. Differences in deprivation, discursive opportunities and the resource basis of mobilization structures can explain differences in protest frequency but also to some extent the evolution of protest over time. Taking up Habermas’ argument regarding the specific perspective of civil society actors in the public debate, we then analyze to which extent the arguments of civil society actors deviate from those of more institutionalized actors. A discursive actor attribution analysis unveils that civil society actors are more sensitive to social problems and grand systemic questions. Moreover, civil society actors are less hesitant to blame actors on the EU level and other EU Member States, even though their overall contribution to the crisis debate is rather marginal.     

Securitization of migration and the far right: the case of Greek security professionals

Since the events of 9/11, security concerns have gained unprecedented dominance on western governments' national and international political agendas; Greece has been no exception. The success or failure of a far right party, like Golden Dawn, depends on the effectiveness of the government to regulate immigration and to develop policies aimed at combating the racism which pervades the political culture of society at this particular juncture, when the country is experiencing severe crisis. The aim is to provide an account of the rationale of the securitization of migration from the perspective of Greek security professionals. We argue that the extreme securitizing perceptions of security professionals have been exploited and assisted by far‐right extremist groups, which instilled racial violence, hate speech/crime into society, resulting in patterned, unreflective, and routinized security practices and discourses which are more in line with the beliefs and values advocated by the extreme right.