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Université de Fribourg

d-Transversals of stable sets and vertex covers in weighted bipartite graphs

Bentz, Cédric ; Costa, Marie-Christine ; Picouleau, Christophe ; Ries, Bernard ; de Werra, Dominique

In: Journal of Discrete Algorithms, 2012, vol. 17, p. 95-102

Let G = (V , E) be a graph in which every vertex v ∈ V has a weight w(v)>=0 and a cost c(v) >=0. Let SG be the family of all maximum-weight stable sets in G. For any integer d 0, a minimum d-transversal in the graph G with respect to SG is a subset of vertices T ⊆ V of minimum total cost such that |T ∩ S| d for every S ∈ SG. In this paper, we present a polynomial-time algorithm to...

Université de Fribourg

Does leaving welfare improve health? Evidence for Germany

Huber, Martin ; Lechner, Michael ; Wunsch, Conny

In: Health economics, 2011, vol. 20, no. 4, p. 484-504

Using exceptionally rich linked administrative and survey information on German welfare recipients we investigate the health effects of transitions from welfare to employment and of assignments to welfare-to-work programmes. Applying semi- parametric propensity score matching estimators we find that employment substantially increases (mental) health. The positive effects are mainly driven by...

Université de Fribourg

Identifying causal mechanisms (primarily) based on inverse probability weighting

Huber, Martin

In: Journal of Applied Econometrics, 2014, vol. 29, no. 6, p. 920-943

This paper demonstrates the identification of causal mechanisms of a binary treatment under selection on observables, (primarily) based on inverse probability weighting; i.e. we consider the average indirect effect of the treatment, which operates through an intermediate variable (or mediator) that is situated on the causal path between the treatment and the outcome, as well as the...

Université de Fribourg

A Test of the Conditional Independence Assumption in Sample Selection Models

Huber, Martin ; Melly, Blaise

In: Journal of Applied Econometrics, 2015, vol. 30, no. 7, p. 1144-1168

Identification in most sample selection models depends on the independence of the regressors and the error terms conditional on the selection probability. All quantile and mean functions are parallel in these models; this implies that quantile estimators cannot reveal any—per assumption non-existing—heterogeneity. Quantile estimators are nevertheless useful for testing the conditional...

Université de Fribourg

Amateurs striving for news production. Can they competewith professional journalism?

Bosshart, Stefan ; Schönhagen, Philomen

In: Studies in Communication Sciences, 2013, vol. 13, no. 2, p. 139-147

tWith the rise of Web 2.0 the discussion about professional journalism changing radically or even becom-ing obsolete in the future has intensified. Up to now, empirical findings mainly stem from research on(micro-)blogging and show its complementary rather than equivalent function compared with profes-sional journalism. Amazingly, the performance of collaborative amateur news websites with an...

Université de Fribourg

Empirical analysis on a keyword-based semantic system

Zhang, Zi-Ke ; Lü, Linyuan ; Liu, Jian-Guo ; Zhou, Tao

In: The European Physical Journal B, 2008, vol. 66, no. 4, p. 557-561

Keywords in scientific articles have found their significance in information filtering and classification. In this article, we empirically investigated statistical characteristics and evolutionary properties of keywords in a very famous journal, namely Proceedings of the National Academy of Science of the United States of America (PNAS), including frequency distribution, temporal scaling...

Université de Fribourg

Heterogeneous network with distance dependent connectivity

Medo, Matúš ; Smrek, Jano

In: The European Physical Journal B, 2008, vol. 63, no. 2, p. 273-278

We investigate a network model based on an infinite regular square lattice embedded in the Euclidean plane where the node connection probability is given by the geometrical distance of nodes. We show that the degree distribution in the basic model is sharply peaked around its mean value. Since the model was originally developed to mimic the social network of acquaintances, to broaden the degree...

Université de Fribourg

A limited resource model of fault-tolerant capability against cascading failure of complex network

Li, P. ; Wang, B.-H. ; Sun, H. ; Gao, P. ; Zhou, Tao

In: The European Physical Journal B, 2008, vol. 62, no. 1, p. 101-104

We propose a novel capacity model for complex networks against cascading failure. In this model, vertices with both higher loads and larger degrees should be paid more extra capacities, i.e. the allocation of extra capacity on vertex i will be proportional to ki γ , where ki is the degree of vertex i and γ > 0 is a free parameter. We have applied this model...