Determining full conditional independence by low-order conditioning

A concentration graph associated with a random vector is an undirected graph where each vertex corresponds to one random variable in the vector. The absence of an edge between any pair of vertices (or variables) is equivalent to full conditional independence between these two variables given all the other variables. In the multivariate Gaussian case, the absence of an edge corresponds to a zero coefficient in the precision matrix, which is the inverse of the covariance matrix. It is well known that this concentration graph represents some of the conditional independencies in the distribution of the associated random vector. These conditional independencies correspond to the "separations" or absence of edges in that graph. In this paper we assume that there are no other independencies present in the probability distribution than those represented by the graph. This property is called the perfect Markovianity of the probability distribution with respect to the associated concentration graph. We prove in this paper that this particular concentration graph, the one associated with a perfect Markov distribution, can be determined by only conditioning on a limited number of variables. We demonstrate that this number is equal to the maximum size of the minimal separators in the concentration graph.Comment: Published in at http://dx.doi.org/10.3150/09-BEJ193 the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

Trade and trade finance developments in 14 developing countries post September 2008 - a World Bank survey

In the aftermath of the Lehman Brothers collapse in September 2008, drop in the supply of trade finance, a critical engine for trade transactions, has become an acute concern for the development community. Banks were increasing pricing on trade finance transactions to cover increased funding costs and higher credit risks, and trade was dropping drastically in most countries, with global trade projected to decline in 2009 for the first time in decades. Yet, little was known about the real impact of the crisis on developing country’s capacity to export. The World Bank has commissioned a firm and bank survey on trade and trade finance developments in developing countries during the first quarter of 2009 to collect field information. In total, 425 firms and 78 banks were surveyed in 14 developing countries across five regions. This paper summarizes the findings of the survey as well as discusses the type of policies governments and international organizations put in place to mitigate the impact of the crisis. In sum, the survey findings confirmed that the global financial crisis has constrained trade finance for exporters and importers in developing countries. But the impact varied by the firm size, sectoral activity, and countries’ integration into the global economy. In particular, SMEs were particularly affected, and export diversification was made more difficult, especially in low income countries. Nevertheless, drop in demand has emerged as the top concern of firms at the time when the survey was conducted in March-April 2009.Banks&Banking Reform,Access to Finance,Debt Markets,Emerging Markets,Economic Theory&Research

Trade Policy and Export Performance in Morocco

Morocco’s trade policy is at a cross-roads. Historically, the country has had a very restrictive import regime that generated substantial transfers to domestic producers. In terms of the simple average of most-favored nation tariffs, Morocco is one of the ten most highly protected markets in the world. Yet, with the signing of the Euro-Med Agreement with the European Union and its implementation since 2000, a decision for the gradual opening of the domestic market through preferential trade liberalization was taken. This choice was subsequently reaffirmed through the conclusion of further free trade agreements with the United States and Turkey. The resulting shift in trade policy paradigms promises to create new opportunities for export-led economic growth and employment generation, while requiring adjustment of domestic producers to the new, more competitive economic environment and additional policy reforms to complement the market opening strategy.Trade, tariffs, services, logistics, export diversification, regional integration, world markets

Duality in Graphical Models

Graphical models have proven to be powerful tools for representing high-dimensional systems of random variables. One example of such a model is the undirected graph, in which lack of an edge represents conditional independence between two random variables given the rest. Another example is the bidirected graph, in which absence of edges encodes pairwise marginal independence. Both of these classes of graphical models have been extensively studied, and while they are considered to be dual to one another, except in a few instances this duality has not been thoroughly investigated. In this paper, we demonstrate how duality between undirected and bidirected models can be used to transport results for one class of graphical models to the dual model in a transparent manner. We proceed to apply this technique to extend previously existing results as well as to prove new ones, in three important domains. First, we discuss the pairwise and global Markov properties for undirected and bidirected models, using the pseudographoid and reverse-pseudographoid rules which are weaker conditions than the typically used intersection and composition rules. Second, we investigate these pseudographoid and reverse pseudographoid rules in the context of probability distributions, using the concept of duality in the process. Duality allows us to quickly relate them to the more familiar intersection and composition properties. Third and finally, we apply the dualization method to understand the implications of faithfulness, which in turn leads to a more general form of an existing result

Taking Stock of Trade Protectionism Since 2008

Following the onset of the financial crisis in September 2008 and the subsequent “Great Trade Collapse” (Baldwin 2009), many countries actively used trade policy instruments as part of their response to the global recession. Governments pursued a mix of trade liberalization, trade promotion, and trade restrictions. The choice of trade policy has varied, with limited use of tariff hikes or antidumping and safeguard actions. Sector-specific support to industries dominated initial responses to the crisis, and there has been increasing resort to nontariff measures. Recent research suggests that vertical specialization—the growth in global supply chains—has played a significant role in limiting the use of traditional protectionist instruments. Pressures on governments to support domestic economic activity may increase, given current gloomy economic prospects and more binding macroeconomic policy constraints, and the number of protectionist measures has recently risen. Open trade cannot be taken for granted, thus the need for monitoring persists.trade, protectionism, financial crisis, trade policy, recession, trade liberalization, trade promotion, trade restrictions, WTO, Doha

Dissection de l’aorte thoracique descendante et de l’aorte abdominale dans la maladie de Takayasu : à propos d’un cas

La dissection aortique est une complication très rare de la maladie de Takayasu.Dans la littérature récente  seulement 14 cas ont été publiés. Nous rapportons le cas d'un maghrébin âgé de 67 ans, présentant une  dissection aigue de l'aorte thoracique descendante et de l'aorte abdominale avec un syndrome inflammatoire,  révélateur d'une maladie de Takayasu. Le type de l'atteinte aortique (type III b, selon la classification de De  Bakey et Standford) confirmé par angioscanner chez notre patient, n'a pas été rapporté. Il nous parait que  l'artérite de Takayasu est sous-estimée chez les malades dépassant l'âge de la 4ème décennie. La forme  tardive de cette pathologie pose un problème de diagnostic différentiel avec la maladie de Horton, selon les critères d'âge et d'ethnie. Actuellement la majorité des auteurs donnent la priorité à l'imagerie médicale, avec ou sans syndrome inflammatoire pour la confirmation du diagnostic de la maladie de TakayasuKey words: Maladie de Takayasu, dissection aortique, angioscanner, diagnostique différenciel, âge, maladie de Horto

Trade Policy and Export Performance in Morocco

Morocco’s trade policy is at a cross-roads. Historically, the country has had a very restrictive import regime that generated substantial transfers to domestic producers. In terms of the simple average of most-favored nation tariffs, Morocco is one of the ten most highly protected markets in the world. Yet, with the signing of the Euro-Med Agreement with the European Union and its implementation since 2000, a decision for the gradual opening of the domestic market through preferential trade liberalization was taken. This choice was subsequently reaffirmed through the conclusion of further free trade agreements with the United States and Turkey. The resulting shift in trade policy paradigms promises to create new opportunities for export-led economic growth and employment generation, while requiring adjustment of domestic producers to the new, more competitive economic environment and additional policy reforms to complement the market opening strategy

Séparation de sources adaptative et estimation des angles d'arrivée pour une antenne linéaire

Une nouvelle application de la séparation adaptative de sources à bande étroite est présentée dans cet article. Elle est basée sur l'indépendance des sources, sur la connaissance a priori du modèle de propagation et sur l'hypothèse d'une antenne linéaire uniforme. En conséquence, une paramétrisation mettant enjeu les angles d'arrivée et les atténuations des sources est imposée à la matrice de séparation. La minimisation adaptative d'un critère par un algorithme du gradient stochastique opérant sur ces paramètres permet de restituer les angles d'arrivée, puis les atténuations et finalement les sources elles-mêmes

Comparing Strategies to Prevent Stroke and Ischemic Heart Disease in the Tunisian Population: Markov Modeling Approach Using a Comprehensive Sensitivity Analysis Algorithm.

Background. Mathematical models offer the potential to analyze and compare the effectiveness of very different interventions to prevent future cardiovascular disease. We developed a comprehensive Markov model to assess the impact of three interventions to reduce ischemic heart diseases (IHD) and stroke deaths: (i) improved medical treatments in acute phase, (ii) secondary prevention by increasing the uptake of statins, (iii) primary prevention using health promotion to reduce dietary salt consumption. Methods. We developed and validated a Markov model for the Tunisian population aged 35–94 years old over a 20-year time horizon. We compared the impact of specific treatments for stroke, lifestyle, and primary prevention on both IHD and stroke deaths. We then undertook extensive sensitivity analyses using both a probabilistic multivariate approach and simple linear regression (metamodeling). Results. The model forecast a dramatic mortality rise, with 111,134 IHD and stroke deaths (95% CI 106567 to 115048) predicted in 2025 in Tunisia. The salt reduction offered the potentially most powerful preventive intervention that might reduce IHD and stroke deaths by 27% (−30240 [−30580 to −29900]) compared with 1% for medical strategies and 3% for secondary prevention. The metamodeling highlighted that the initial development of a minor stroke substantially increased the subsequent probability of a fatal stroke or IHD death. Conclusions. The primary prevention of cardiovascular disease via a reduction in dietary salt consumption appeared much more effective than secondary or tertiary prevention approaches. Our simple but comprehensive model offers a potentially attractive methodological approach that might now be extended and replicated in other contexts and populations