Some Properties of the Hazard Function of the Two-Mutation Clonal Expansion Model

We discuss the hazard function of the two-mutation clonal expansion model with time-dependent parameters, with particular emphasis on identifiability of the parameters. We explicitly construct identifiable parameter combinations, and illustrate the properties of the hazard function under perturbations of the underlying biological parameters.     

The intersection of social protection and mobilities: a move towards a ‘Practical Utopia’ research agenda

Currently, a number of contributions in mobility studies are looking for fruitful intersections with other ‘adjacent’ approaches . In this spirit, our theoretical paper argues to study one particular aspect: the intersection of social protection and mobilities. Currently, the provision of social services in the ‘West’ is strongly entrenched within nation-state logics, which assume that clients’ immobility is a precondition of service delivery and that national citizenship is the desirable conditionality of gaining social rights. To overcome such a wide-spread conflation of social security with state security, we introduce the heuristic concept ‘social protection’. It allows social security to be imagined beyond a state-centric perspective and avoids the pitfalls of either a citizenship or a migration approach by taking on a mobility perspective. Thus, for scholars anchored in mobility studies we propose how to develop a social security perspective in a progressive way. For readers from other areas, e.g. citizenship, migration or social policy, we will show how a mobility perspective enriched by a No Border approach can overcome a narrow Western, statist and static perspective on social security. Our goal is to conceptually open up what we call a ‘practical utopia’ research agenda, one that expands our political horizons for future and present socialities.     

Forms of Capital and Habitus in the Decision to Go on Academic Exchange

Although Canadian universities have made internationalization a strategic priority, only few Canadian students currently participate in any international study opportunities. Drawing on interviews with Canadian students who were about to spend some of their undergraduate education abroad as exchange students, or had recently returned from a study exchange, we argue that despite the importance of relatively high costs associated with international study experiences, cultural factors play a more important role in enabling the decision to study abroad. Being habitually exposed to travel in one's family, and having been encouraged to travel independently as a teenager or young adult emerge as important precursors to our participants’ decision to take part in study exchanges. Although one needs to engage critically with university administrators’ current preoccupation with internationalization, being exposed to an extended time abroad has shown to have positive effects, especially for otherwise underprivileged students. Given the exploratory nature of this study, we conclude with suggestions for further research aimed at confirming our findings and developing policy.     

I Am Woman,Hear Me Tweet! Gender Differences in Twitter Use among Congressional Candidates

This study synthesizes two theoretical literatures to explain gender differences in Twitter usage and effectiveness among US Congressional candidates. The first suggests that candidates in perceived disadvantaged positions, females in this case, innovate to improve their chances of success, and the second, that female politicians often adopt stereotypically masculine behaviors to be successful. On the basis of these theories, we hypothesize and confirm that female candidates are more likely than males to integrate Twitter into their campaigns, but our results are less conclusive regarding a difference in the likelihood that females use negative campaigning tactics via Twitter. Our results also indicate that those females who use Twitter more than their male counterparts tended to do better electorally, but this difference is conditional. Female Republican candidates who tweeted more increased their vote share, but the opposite is true for Democrats. We speculate that this differential effect may be a product of different audiences for social media in each party’s electorate.     

Was ist hier los?

In our prior article in this issue, we establish that although they are related, organizational and group dynamics are in fact very different. In this second article, we go on to discuss some of the challenges that this poses for consultants. We describe the interplay of factors affecting the development of the dynamics within an organization and explore approaches to acquiring practical knowledge about an organization’s dynamics. Finally, we ask how useful group dynamics skills are for providing consultancy services within and to organizations and consider where and how specific organizational dynamics skills can be acquired.     

Birnbaum–Saunders sample selection model

The sample selection bias problem occurs when the outcome of interest is only observed according to some selection rule, where there is a dependence structure between the outcome and the selection rule. In a pioneering work, J. Heckman proposed a sample selection model based on a bivariate normal distribution for dealing with this problem. Due to the non-robustness of the normal distribution, many alternatives have been introduced in the literature by assuming extensions of the normal distribution like the Student-t and skew-normal models. One common limitation of the existent sample selection models is that they require a transformation of the outcome of interest, which is common R+-valued, such as income and wage. With this, data are analyzed on a non-original scale which complicates the interpretation of the parameters. In this paper, we propose a sample selection model based on the bivariate Birnbaum–Saunders distribution, which has the same number of parameters that the classical Heckman model. Further, our associated outcome equation is R+-valued. We discuss estimation by maximum likelihood and present some Monte Carlo simulation studies. An empirical application to the ambulatory expenditures data from the 2001 Medical Expenditure Panel Survey is presented.     

Industrial Relations and Trade Union Effects on Innovation in Germany

ABSTRACT: This paper provides a thoretical and empirical evaluation of unions’effects on innovative activity, focussing on institutional details and country-specific factors. We represent results of an econometric investigation for Germany using data at the industry and establishment level. In contrast to US studies, no statistically significant negative influence of unions on innovative activity shows up from industry-level data. Establishment-level data, however, indicate that the presence of a works council is positive for R & D if union density is not “too high”. This is in line with the more cooperative nature of industrial relations in Germany.