37,116 research outputs found
Emerging pluralist politics in Mozambique: the Frelimo-Renamo party system
In 1992, the Mozambican civil war was brought to a close, marking the beginning of a 'pacted' and fundamentally successful process of democratic change. Despite the extreme poverty of the country, Mozambique has managed to introduce a formally competitive electoral regime, in which movements that were formerly in violent opposition to one another have moved towards fragile pluralist practices, in marked contrast to, for example, Angola, whose peace process quickly unravelled. This paper examines the emergence of a two party system in Mozambique, in which the former Renamo guerrilla fighters appear to have embraced the possibilities of peace. Ultimately, however, Carbone warns against undue optimism, and highlights the weaknesses of the system that are still to be resolved. For all that the country has adopted a formally competitive political system, it continues to fall short of fully democratic and liberal practices
Independencies Induced from a Graphical Markov Model After Marginalization and Conditioning: The R Package ggm
We describe some functions in the R package ggm to derive from a given Markov model, represented by a directed acyclic graph, different types of graphs induced after marginalizing over and conditioning on some of the variables. The package has a few basic functions that find the essential graph, the induced concentration and covariance graphs, and several types of chain graphs implied by the directed acyclic graph (DAG) after grouping and reordering the variables. These functions can be useful to explore the impact of latent variables or of selection effects on a chosen data generating model.
Chain graph models of multivariate regression type for categorical data
We discuss a class of chain graph models for categorical variables defined by
what we call a multivariate regression chain graph Markov property. First, the
set of local independencies of these models is shown to be Markov equivalent to
those of a chain graph model recently defined in the literature. Next we
provide a parametrization based on a sequence of generalized linear models with
a multivariate logistic link function that captures all independence
constraints in any chain graph model of this kind.Comment: Published in at http://dx.doi.org/10.3150/10-BEJ300 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Star graphs induce tetrad correlations: for Gaussian as well as for binary variables
Tetrad correlations were obtained historically for Gaussian distributions
when tasks are designed to measure an ability or attitude so that a single
unobserved variable may generate the observed, linearly increasing dependences
among the tasks. We connect such generating processes to a particular type of
directed graph, the star graph, and to the notion of traceable regressions.
Tetrad correlation conditions for the existence of a single latent variable are
derived. These are needed for positive dependences not only in joint Gaussian
but also in joint binary distributions. Three applications with binary items
are given.Comment: 21 pages, 2 figures, 5 table
Matrix representations and independencies in directed acyclic graphs
For a directed acyclic graph, there are two known criteria to decide whether
any specific conditional independence statement is implied for all
distributions factorized according to the given graph. Both criteria are based
on special types of path in graphs. They are called separation criteria because
independence holds whenever the conditioning set is a separating set in a graph
theoretical sense. We introduce and discuss an alternative approach using
binary matrix representations of graphs in which zeros indicate independence
statements. A matrix condition is shown to give a new path criterion for
separation and to be equivalent to each of the previous two path criteria.Comment: Published in at http://dx.doi.org/10.1214/08-AOS594 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Mixing Flows on Moduli Spaces of Flat Bundles over Surfaces
We extend Teichmueller dynamics to a flow on the total space of a flat bundle
of deformation spaces of representations of the fundamental group of a fixed
surface S in a Lie group G. The resulting dynamical system is a continuous
version of the action of the mapping class group of S on the deformation space.
We observe how ergodic properties of this action relate to this flow. When G is
compact, this flow is strongly mixing over each component of the derormation
space and of each stratum of the Teichmueller unit sphere bundle over the
Riemann moduli space. We prove ergodicity for the analogous lift of the
Weil-Petersson geodesic local. flow.Comment: 18 pages, no figures, presented at the Oxford conference honoring
Nigel Hitchin's 70th birthday (9 September 2016) and to appear in the
companion volume published by Oxford University Pres
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