Página 13 dos resultados de 535 itens digitais encontrados em 0.002 segundos

Debt and economic growth in the European Union : what causes what?

Ferreira, Cândida
Fonte: ISEG – Departamento de Economia Publicador: ISEG – Departamento de Economia
Tipo: Trabalho em Andamento
Publicado em //2014 Português
Relevância na Pesquisa
26.54%
This paper contributes to the empirical investigation of the causality relations between real GDP growth and the growth of three debt categories, namely public, foreign and private debt, in the universe of the 28 European Union countries during the past decade. By using panel Granger causality estimations, we find nonstatistically significant causality between foreign debt and economic growth and the limited importance of the causality between private debt and real GDP growth. On the contrary, the results obtained show statistically relevant bidirectional causality relations between public debt and economic growth, and this is true before and after the outbreak of the recent financial crisis. Moreover, there is clear evidence of economic growth’s contribution to the decrease in public debt.

Interactions of viral pathogens on hospital admissions for pneumonia, croup and chronic obstructive pulmonary diseases: results of a multivariate time-series analysis

UPSHUR, R. E. G.; MOINEDDIN, R.; CRIGHTON, E. J.; MAMDANI, M.
Fonte: Cambridge University Press Publicador: Cambridge University Press
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.55%
Co-circulation of respiratory syncytial virus (RSV) and influenza has made the partitioning of morbidity and mortality from each virus difficult. Given the interaction between chronic obstructive lung disease (COPD) and pneumonia, often one can be mistaken for the other. Multivariate time-series methodology was applied to examine the impact of RSV and influenza on hospital admissions for bronchiolitis, pneumonia, and COPD. The Granger Causality Test, used to determine the causal relationship among series, showed that COPD and pneumonia are not influenced by RSV (P=0·2999 and 0·7725), but RSV does influence bronchiolitis (P=0·0001). Influenza was found to influence COPD, pneumonia, and bronchiolitis (P<0·0001). The use of multivariate time series and Granger causality applied to epidemiological data clearly illustrates the significant contribution of influenza and RSV to morbidity in the population.

A cerebellar thalamic cortical circuit for error-related cognitive control

Ide, Jaime S.; Li, Chiang-shan Ray
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.47%
Error detection and behavioral adjustment are core components of cognitive control. Numerous studies have focused on the anterior cingulate cortex (ACC) as a critical locus of this executive function. Our previous work showed greater activation in the dorsal ACC and subcortical structures during error detection, and activation in the ventrolateral prefrontal cortex (VLPFC) during post-error slowing (PES) in a stop signal task (SST). However, the extent of error-related cortical or subcortical activation across subjects was not correlated with VLPFC activity during PES. So then, what causes VLPFC activation during PES? To address this question, we employed Granger causality mapping (GCM) and identified regions that Granger caused VLPFC activation in 54 adults performing the SST during fMRI. These brain regions, including the supplementary motor area (SMA), cerebellum, a pontine region, and medial thalamus, represent potential targets responding to errors in a way that could influence VLPFC activation. In confirmation of this hypothesis, the error-related activity of these regions correlated with VLPFC activation during PES, with the cerebellum showing the strongest association. The finding that cerebellar activation Granger causes prefrontal activity during behavioral adjustment supports a cerebellar function in cognitive control. Furthermore...

Altered Effective Connectivity Network of the Amygdala in Social Anxiety Disorder: A Resting-State fMRI Study

Liao, Wei; Qiu, Changjian; Gentili, Claudio; Walter, Martin; Pan, Zhengyong; Ding, Jurong; Zhang, Wei; Gong, Qiyong; Chen, Huafu
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 22/12/2010 Português
Relevância na Pesquisa
26.55%
The amygdala is often found to be abnormally recruited in social anxiety disorder (SAD) patients. The question whether amygdala activation is primarily abnormal and affects other brain systems or whether it responds “normally” to an abnormal pattern of information conveyed by other brain structures remained unanswered. To address this question, we investigated a network of effective connectivity associated with the amygdala using Granger causality analysis on resting-state functional MRI data of 22 SAD patients and 21 healthy controls (HC). Implications of abnormal effective connectivity and clinical severity were investigated using the Liebowitz Social Anxiety Scale (LSAS). Decreased influence from inferior temporal gyrus (ITG) to amygdala was found in SAD, while bidirectional influences between amygdala and visual cortices were increased compared to HCs. Clinical relevance of decreased effective connectivity from ITG to amygdala was suggested by a negative correlation of LSAS avoidance scores and the value of Granger causality. Our study is the first to reveal a network of abnormal effective connectivity of core structures in SAD. This is in support of a disregulation in predescribed modules involved in affect control. The amygdala is placed in a central position of dysfunction characterized both by decreased regulatory influence of orbitofrontal cortex and increased crosstalk with visual cortex. The model which is proposed based on our results lends neurobiological support towards cognitive models considering disinhibition and an attentional bias towards negative stimuli as a core feature of the disorder.

Effective connectivity: Influence, causality and biophysical modeling

Valdes-Sosa, Pedro A.; Roebroeck, Alard; Daunizeau, Jean; Friston, Karl
Fonte: Academic Press Publicador: Academic Press
Tipo: Artigo de Revista Científica
Publicado em 15/09/2011 Português
Relevância na Pesquisa
26.55%
This is the final paper in a Comments and Controversies series dedicated to “The identification of interacting networks in the brain using fMRI: Model selection, causality and deconvolution”. We argue that discovering effective connectivity depends critically on state-space models with biophysically informed observation and state equations. These models have to be endowed with priors on unknown parameters and afford checks for model Identifiability. We consider the similarities and differences among Dynamic Causal Modeling, Granger Causal Modeling and other approaches. We establish links between past and current statistical causal modeling, in terms of Bayesian dependency graphs and Wiener–Akaike–Granger–Schweder influence measures. We show that some of the challenges faced in this field have promising solutions and speculate on future developments.

eConnectome: A MATLAB Toolbox for Mapping and Imaging of Brain Functional Connectivity

He, Bin; Dai, Yakang; Astolfi, Laura; Babiloni, Fabio; Yuan, Han; Yang, Lin
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.55%
We have developed a MATLAB-based toolbox, eConnectome (electrophysiological connectome), for mapping and imaging functional connectivity at both the scalp and cortical levels from the electroencephalogram (EEG), as well as from the electrocorticogram (ECoG). Graphical user interfaces were designed for interactive and intuitive use of the toolbox. Major functions of eConnectome include EEG/ECoG preprocessing, scalp spatial mapping, cortical source estimation, connectivity analysis, and visualization. Granger causality measures such as Directed Transfer Function and adaptive Directed Transfer Function were implemented to estimate the directional interactions of brain functional networks, over the scalp and cortical sensor spaces. Cortical current density inverse imaging was implemented using a generic realistic geometry brain-head model from scalp EEGs. Granger causality could be further estimated over the cortical source domain from the inversely reconstructed cortical source signals as derived from the scalp EEG. Users may implement other connectivity estimators in the framework of eConnectome for various applications. The toolbox package is open-source and freely available at http://econnectome.umn.edu under the GNU general public license for noncommercial and academic uses.

Behavior related pauses in simple spike activity of mouse Purkinje cells are linked to spike rate modulation

Cao, Ying; Maran, Selva K.; Dhamala, Mukesh; Jaeger, Dieter; Heck, Detlef H.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 20/06/2012 Português
Relevância na Pesquisa
26.55%
Purkinje cells (PCs) in the mammalian cerebellum express high frequency spontaneous activity with average spike rates between 30 and 200 Hz. Cerebellar nuclear (CN) neurons receive converging input from many PCs resulting in a continuous barrage of inhibitory inputs. It has been hypothesized that pauses in PC activity trigger increases in CN spiking activity. A prediction derived from this hypothesis is that pauses in PC simple spike activity represent relevant behavioral or sensory events. Here we asked whether pauses in the simple spike activity of PCs related to either fluid licking or respiration, play a special role in representing information about behavior. Both behaviors are widely represented in cerebellar PC simple spike activity. We recorded PC activity in the vermis and lobus simplex of head fixed mice while monitoring licking and respiratory behavior. Using cross correlation and Granger causality analysis we examined whether short ISIs had a different temporal relation to behavior than long ISIs or pauses. Behavior related simple spike pauses occurred during low-rate simple spike activity in both licking and breathing related PCs. Granger causality analysis revealed causal relationships between simple spike pauses and behavior. However...

Optogenetically Induced Seizure and the Longitudinal Hippocampal Network Dynamics

Osawa, Shin-ichiro; Iwasaki, Masaki; Hosaka, Ryosuke; Matsuzaka, Yoshiya; Tomita, Hiroshi; Ishizuka, Toru; Sugano, Eriko; Okumura, Eiichi; Yawo, Hiromu; Nakasato, Nobukazu; Tominaga, Teiji; Mushiake, Hajime
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 10/04/2013 Português
Relevância na Pesquisa
26.5%
Epileptic seizure is a paroxysmal and self-limited phenomenon characterized by abnormal hypersynchrony of a large population of neurons. However, our current understanding of seizure dynamics is still limited. Here we propose a novel in vivo model of seizure-like afterdischarges using optogenetics, and report on investigation of directional network dynamics during seizure along the septo-temporal (ST) axis of hippocampus. Repetitive pulse photostimulation was applied to the rodent hippocampus, in which channelrhodopsin-2 (ChR2) was expressed, under simultaneous recording of local field potentials (LFPs). Seizure-like afterdischarges were successfully induced after the stimulation in both W-TChR2V4 transgenic (ChR2V-TG) rats and in wild type rats transfected with adeno-associated virus (AAV) vectors carrying ChR2. Pulse frequency at 10 and 20 Hz, and a 0.05 duty ratio were optimal for afterdischarge induction. Immunohistochemical c-Fos staining after a single induced afterdischarge confirmed neuronal activation of the entire hippocampus. LFPs were recorded during seizure-like afterdischarges with a multi-contact array electrode inserted along the ST axis of hippocampus. Granger causality analysis of the LFPs showed a bidirectional but asymmetric increase in signal flow along the ST direction. State space presentation of the causality and coherence revealed three discrete states of the seizure-like afterdischarge phenomenon: 1) resting state; 2) afterdischarge initiation with moderate coherence and dominant septal-to-temporal causality; and 3) afterdischarge termination with increased coherence and dominant temporal-to-septal causality. A novel in vivo model of seizure-like afterdischarge was developed using optogenetics...

Altered Causal Connectivity of Resting State Brain Networks in Amnesic MCI

Liang, Peipeng; Li, Zhihao; Deshpande, Gopikrishna; Wang, Zhiqun; Hu, Xiaoping; Li, Kuncheng
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 10/03/2014 Português
Relevância na Pesquisa
26.55%
Most neuroimaging studies of resting state networks in amnesic mild cognitive impairment (aMCI) have concentrated on functional connectivity (FC) based on instantaneous correlation in a single network. The purpose of the current study was to investigate effective connectivity in aMCI patients based on Granger causality of four important networks at resting state derived from functional magnetic resonance imaging data – default mode network (DMN), hippocampal cortical memory network (HCMN), dorsal attention network (DAN) and fronto-parietal control network (FPCN). Structural and functional MRI data were collected from 16 aMCI patients and 16 age, gender-matched healthy controls. Correlation-purged Granger causality analysis was used, taking gray matter atrophy as covariates, to compare the group difference between aMCI patients and healthy controls. We found that the causal connectivity between networks in aMCI patients was significantly altered with both increases and decreases in the aMCI group as compared to healthy controls. Some alterations were significantly correlated with the disease severity as measured by mini-mental state examination (MMSE), and California verbal learning test (CVLT) scores. When the whole-brain signal averaged over the entire brain was used as a nuisance co-variate...

Do emissions and income have a common trend? A country-specific, time-series, global analysis, 1970-2008

PARUOLO PAOLO; MURPHY Ben; JANSSENS-MAENHOUT Greet
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Articles in periodicals and books Formato: Printed
Português
Relevância na Pesquisa
26.5%
This paper analyzes the relation between income and emissions in the period 1970-2008, for all world countries. We consider time-series of CO2, SO2 and GWP100, and use Vector Autoregressive models that allow for nonstationarity and cointegration. At 5\% significance level, income and emissions are found to be driven by unrelated random walks with drift (respectively by a common random walk with drift) in about 70% (respectively 25%) of cases; in the remaining cases the variables are trend-stationary. Tests of Granger-causality show evidence of both directions of causality. For the case of unrelated stochastic trends, we almost never find income driving emissions, as predicted by a consumption-function interpretation. These causality results and the absence of a common trend challenge the main implications of the Environmental Kuznets Curve, namely that the dominant direction of causality should be from income to emissions, and that for increasing levels of income, emissions should tend to decrease.; JRC.DDG.01-Econometrics and applied statistics

Búsqueda de relaciones causales para aplicaciones en cardiología y psiquiatría

Prado Cumplido, Mario de
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Tese de Doutorado Formato: application/pdf
Português
Relevância na Pesquisa
26.55%
En esta tesis se presenta un estudio sobre la teoría de la causalidad y se desarrollan nuevas técnicas de inferencia causal en datos discretos y en señales continuas. Estos métodos se han utilizado para avanzar en el conocimiento de dos problemas médicos: uno en el campo de la psiquiatría y otro en cardiología. Los métodos clásicos para inferir relaciones causales a partir de muestras se basan en múltiples análisis de independencia estadística condicional. Estos métodos no dan buenos resultados cuando el número de variables aleatorias es elevado. Por el contrario, las técnicas de aprendizaje máquina son razonablemente robustas frente a problemas de alta dimensionalidad. Se han sustituido los test de independencia por una batería de clasificadores en el algoritmo de búsqueda causal propuesto. En la tesis se muestra cómo es posible identficar las relaciones causales en funci on del número de variables relevantes en una clasficaci on. Se ha ensayado con dos clasificadores, un k vecinos más próximos y una máquina de vectores soporte (SVM). Para aligerar la carga computacional impuesta por el gran número de clasificadores a entrenar, se ha recurrido a una permutación aleatoria para obtener la salida de problemas de menor dimensión a partir de máquinas entrenadas en dimensión superior. Se ha empleado la téccnica de remuestreo "bootstrap" para etapas intermedias de estos algoritmos. Para señales en tiempo continuo...

An empirical analysis of the relationships between crude oil, gold and stock markets

Coronado, Semei; Jiménez-Rodríguez, Rebeca; Rojas, Omar
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/10/2015 Português
Relevância na Pesquisa
26.5%
This paper analyzes the direction of the causality between crude oil, gold and stock markets for the largest economy in the world with respect to such markets, the US. To do so, we apply non-linear Granger causality tests. We find a nonlinear causal relationship among the three markets considered, with the causality going in all directions, when the full sample and different subsamples are considered. However, we find a unidirectional nonlinear causal relationship between the crude oil and gold market (with the causality only going from oil price changes to gold price changes) when the subsample runs from the first date of any year between the mid-1990s and 2001 to last available data (February 5, 2015). The latter result may explain the lack of consensus existing in the literature about the direction of the causal link between the crude oil and gold markets.; Comment: submitted to Energy Economics, 19 pages, 1 figure

Robustly estimating the flow direction of information in complex physical systems

Nolte, Guido; Ziehe, Andreas; Nikulin, Vadim V.; Schlögl, Alois; Krämer, Nicole; Brismar, Tom; Müller, Klaus-Robert
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/12/2007 Português
Relevância na Pesquisa
26.55%
We propose a new measure to estimate the direction of information flux in multivariate time series from complex systems. This measure, based on the slope of the phase spectrum (Phase Slope Index) has invariance properties that are important for applications in real physical or biological systems: (a) it is strictly insensitive to mixtures of arbitrary independent sources, (b) it gives meaningful results even if the phase spectrum is not linear, and (c) it properly weights contributions from different frequencies. Simulations of a class of coupled multivariate random data show that for truly unidirectional information flow without additional noise contamination our measure detects the correct direction as good as the standard Granger causality. For random mixtures of independent sources Granger Causality erroneously yields highly significant results whereas our measure correctly becomes non-significant. An application of our novel method to EEG data (88 subjects in eyes-closed condition) reveals a strikingly clear front-to-back information flow in the vast majority of subjects and thus contributes to a better understanding of information processing in the brain.; Comment: 5 pages, 4 figures

Transfer Entropy as a Log-likelihood Ratio

Barnett, Lionel; Bossomaier, Terry
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.55%
Transfer entropy, an information-theoretic measure of time-directed information transfer between joint processes, has steadily gained popularity in the analysis of complex stochastic dynamics in diverse fields, including the neurosciences, ecology, climatology and econometrics. We show that for a broad class of predictive models, the log-likelihood ratio test statistic for the null hypothesis of zero transfer entropy is a consistent estimator for the transfer entropy itself. For finite Markov chains, furthermore, no explicit model is required. In the general case, an asymptotic chi-squared distribution is established for the transfer entropy estimator. The result generalises the equivalence in the Gaussian case of transfer entropy and Granger causality, a statistical notion of causal influence based on prediction via vector autoregression, and establishes a fundamental connection between directed information transfer and causality in the Wiener-Granger sense.

Stock market comovements: nonlinear approach for 48 countries

Ferreira, Paulo; Dionísio, Andreia; Movahed, S. M. S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/02/2015 Português
Relevância na Pesquisa
26.55%
This paper examines the stock market comovements using basically three different approaches. Firstly, we used the most common linear analysis, based on cointegration and Granger causality tests; secondly we applied a nonlinear approach, using mutual information to analyze nonlinear dependence. Since underlying data sets are affected by non-stationarities, we also applied MF-DFA and MF-DXA in order to examine the multifractality nature of data and to analyze the relationship and mutual interaction between pairs of series, respectively. The overall results are quite interesting, since we found only 170 pair of stock markets cointegrated, and according to the Granger causality and mutual information we realized that the strongest relations lies between emerging markets, and between emerging and frontier markets. According to scaling exponent given by MF-DFA, $h(q=2)>1$, we found that all underlying data belong to non-stationary process. There is no cross-over in the fluctuation functions determined by MF-DFA method confirmed that mentioned approach could remove trends embedded in the data sets. The nature of cross-correlation exponent based on Mf-DXA is almost multifractal for all stock market pairs. The empirical relation, $h_{xy}(q)=[h_{xx}(q)+h_{yy}(q)]/2$ was confirmed just for $q>0$...

Directed Information Graphs

Quinn, Christopher J.; Kiyavash, Negar; Coleman, Todd P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
26.55%
We propose a graphical model for representing networks of stochastic processes, the minimal generative model graph. It is based on reduced factorizations of the joint distribution over time. We show that under appropriate conditions, it is unique and consistent with another type of graphical model, the directed information graph, which is based on a generalization of Granger causality. We demonstrate how directed information quantifies Granger causality in a particular sequential prediction setting. We also develop efficient methods to estimate the topological structure from data that obviate estimating the joint statistics. One algorithm assumes upper-bounds on the degrees and uses the minimal dimension statistics necessary. In the event that the upper-bounds are not valid, the resulting graph is nonetheless an optimal approximation. Another algorithm uses near-minimal dimension statistics when no bounds are known but the distribution satisfies a certain criterion. Analogous to how structure learning algorithms for undirected graphical models use mutual information estimates, these algorithms use directed information estimates. We characterize the sample-complexity of two plug-in directed information estimators and obtain confidence intervals. For the setting when point estimates are unreliable...

GDP and life expectancy in Italy and Spain over the long-run (1861-2008) : insights from a timeseries approach

Felice, Emanuele; Pujol Andreu, Josep
Fonte: Universitat Autònoma de Barcelona. Unitat d'Història Econòmica Publicador: Universitat Autònoma de Barcelona. Unitat d'Història Econòmica
Tipo: Trabalho em Andamento Formato: application/pdf
Publicado em //2013 Português
Relevância na Pesquisa
26.55%
The article presents and discusses long-run series of per capita GDP and life expectancy for Italy and Spain (1861-2008). After refining the available estimates in order to make them comparable and with the avail of the most up-to-date researches, the main changes in the international economy and in technological and sociobiological regimes are used as analytical frameworks to re-assess the performances of the two countries; then structural breaks are searched for and Granger causality between the two variables is investigated. The long-run convergence notwithstanding, significant cyclical differences between the two countries can be detected: Spain began to modernize later in GDP, with higher volatility in life expectancy until recent decades; by contrast, Italy showed a more stable pattern of life expectancy, following early breaks in per capita GDP, but also a negative GDP break in the last decades. Our series confirm that, whereas at the early stages of development differences in GDP tend to mirror those in life expectancy, this is no longer true at later stages of development, when, if any, there seems to be a negative correlation between GDP and life expectancy: this finding is in line with the thesis of a non-monotonic relation between life expectancy and GDP and is supported by tests of Granger causality.

O mercado de debêntures e o financiamento produtivo no Brasil: uma análise de cointegração e causalidade; The market of corporate debentures and the financing of productive sector in Brazil: a cointegration and causality analysis

Pimentel, Renê Coppe; Peres, Edna Ferreira; Lima, Gerlando Augusto Sampaio Franco de
Fonte: Universidade de São Paulo. Faculdade de Economia, Administração e Contabilidade de RP Publicador: Universidade de São Paulo. Faculdade de Economia, Administração e Contabilidade de RP
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; ; ; ; Formato: application/pdf
Publicado em 01/04/2011 Português
Relevância na Pesquisa
26.55%
This paper analyzes the evolution of the Brazilian corporate debt market and its role on corporate financing from 1994 to 2009. Besides the description of the corporate debt market, the paper analyzes, by using co-integration and causality analysis, if there is long-term relationship between corporate debt market and Brazilian economic growth and the direction of the relationship. Additionally, the corporate debt market is compared to the banking market as complementary and competitive instrument of Brazilian productive financing. Tests suggest that there is significant co-integration between the variables under analysis and, in general, the corporate debt market is Granger-cause of economic growth, which means that there is significant influence of debt volume growth on stimulating economic growth. It was also verified that the corporate debt market seems to be more relevant than the banking market in influencing economic growth.; Este artigo analisa a evolução do mercado brasileiro de debêntures e seu papel no financiamento empresarial entre 1995 e 2009. Além da descrição do mercado de debêntures, o artigo estuda, por meio de análise de cointegração e causalidade, a relação temporal entre o mercado de debêntures e o crescimento econômico brasileiro. Adicionalmente...

Integração espacial no mercado brasileiro de café arábica; Integração espacial no mercado brasileiro de café arábica

Nogueira, Fernando Tadeu Pongelupe; Aguiar, Danilo R. D.; Lima, João Eustáquio de
Fonte: Nova Economia; Nova Economia Publicador: Nova Economia; Nova Economia
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Formato: application/pdf
Publicado em 03/06/2009 Português
Relevância na Pesquisa
26.55%
Este estudo analisa a integração espacial do mercado de café arábica nos dois principais estados produtores no Brasil. Os resultados do teste de raiz unitáriaDickey-Fuller Aumentado (ADF) mostram que todas as séries de preços são integradas de ordem 1, I(1). Os resultados do teste de co-integração de Johansen sugerem que todas as séries são co-integradas. Conclui-se, pois, que os mercados de café arábica das regiões produtoras de Minas Gerais e São Paulo são integrados espacialmente, ou seja, um choque de oferta ou demanda em um desses mercados afeta os preços de café arábica nos demais mercados. Outra constatação, decorrente da estimação de um modelo de correção de erros e da aplicação do Teste de Causalidade de Granger é que a região do Cerrado de Minas Gerais Granger-causa os preços das demais regiões. Tal constatação contraria a expectativa de que a região Sul de Minas, uma das maiores produtoras e exportadoras de café arábica do Brasil, iniciasse as variações de preços. Assim, os resultados da pesquisa sugerem que o mercado brasileiro de café é eficiente, uma vez que as informações têm fluído rapidamente entre os agentes desse mercado, permitindo que os mecanismos de arbitragem e a Lei do Preço Único funcionem a contento.; This study analyzes spatial integration in the arabica coffee market of the two main producer states in Brazil. The results of the Dickey-Fuller Augmented (DFA) unit root testshow that all price series are integrated of first order...

The South African business cycle: What has changed?

Burger,Philippe
Fonte: South African Journal of Economic and Management Sciences Publicador: South African Journal of Economic and Management Sciences
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 Português
Relevância na Pesquisa
26.55%
This paper identifies the basic empirical characteristics and changes of the South African business cycle since 1960. As such, the paper examines changes in volatility as well as the co-movement between several national account variables and real GDP. To examine the co-movements the paper follows Kydland and Prescott, Gavin and Kydland as well as Bergman, Bordo and Jonung and uses correlation coefficients and Granger causality tests. Following Ramos, the paper extends the results of the Granger causality tests using variance decomposition analysis in the context of a VAR (vector auto regression) to establish the contribution that selected national account variables make to the h-period-ahead forecast error variance of themselves and the other variables included in the VARs. The paper indicates that since 1994 volatility in the South African economy decreased significantly, while durable consumption appears to lead the business cycle.