177,385 research outputs found
econet: An R Package for Parameter-Dependent Network Centrality Measures
No full textThe R package econet provides methods for estimating parameter-dependent network centrality measures with linear-in-means models. Both nonlinear least squares and maximum likelihood estimators are implemented. The methods allow for both link and node heterogeneity in network effects, endogenous network formation and the presence of unconnected nodes. The routines also compare the explanatory power of parameter-dependent network centrality measures with those of standard measures of network centrality. Benefits and features of the econet package are illustrated using data from Battaglini and Patacchini (2018) and Battaglini, Leone Sciabolazza, and Patacchini (2020)
Testing the exogeneity assumption in panel data models with "non classical" disturbances
No full textThis paper is concerned with the use of the Durbin-Wu-Hausman test for correlated effects with panel data. The assumptions underlying the construction of the statistic are too strong in many empirical cases. The consequences of deviations from the basic assumptions are investigated. The size distortion is assessed. In the case of measurement error, the Hausman test is found to be a test of the difference in asymptotic biases of between and within group estimators. However, its 'size' is sensitive to the relative magnitude of the intra-group and inter-group variations of the covariates, and can be so large as to preclude the use of the statistic in this case. We show to what extent some assumptions can be relaxed in a panel data context and we discuss an alternative robust formulation of the test. Power considerations are presented
Unobservable factors and panel data sets: an investigation in the labour market
No full textThis paper investigates the effects of unobservable factors that, as is well-known, contaminate two of the variables most used in labour market research, namely the stock of unemployment and the stock of vacancies. Using a matching function framework, we compare different panel data estimators using a number of appropriate Hausman tests robust to deviations from the classical errors assumptions. The relevance of the choice of the model specification is underlined. It is shown to what extent conclusions lacking a rigorous statistical analysis may be misleading
On the estimation of covariance matrices using panel data artificial regressions
No full textThe use of artificial regressions to compute the variance of the difference of pairs of panel data estimators that cannot be ranked in terms of efficiency is considered. It is illustrated how it is possible to get (asymtotically) valid estimators of covariance matrices for differences between estimators when the assumption that the error term in the auxiliary model is IID is violated. We distinguish two possible deviations, one leading only to a non-spherical-within groups covariance matrix and the second leading to a non-spherical-between-groups covariance matrix also. It is shown to what extent the use of an artificial regression with panel data can lead to a robust estimator of the covariance matrix in the first case whereas it leads to a non valid estimator in the second. An alternative step by step procedure is presented
Approcci postdittivi sulle scelte locazionali degli impianti termali fra antichità e alto medioevo. Il caso toscano
No full text
Analisi computerizzata del segnale a R.F. dei tessuti oculari e delle orbite: acquisizione del segnale
No full textGeography and economic performance: exploratory spatial data analysis for Great Britain
No full textThis paper uses the techniques of exploratory spatial data analysis to analyse patterns of spatial association for different indicators of economic performance, and in so doing identify and describe the spatial structure of economic performance for Great Britain. This approach enables us to identify a number of significant local regimes – clusters of areas in which income per worker differs significantly from the global average – and investigate whether these come about primarily through spatial association in occupational composition or in productivity. Our results show that the contributions of occupational composition and productivity vary significantly across local regimes. The ‘winner’s circle’ of areas in the south and east of England benefits from both above average levels of productivity and better than average occupational composition, while the low income regime in the north of England suffers particularly from poor occupational composition
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Different mechanism of tachykinin NK2 receptor blockade by SR 48968 and MEN 10,627 in the guinea-pig isolated gallbladder and colon
No full textThe mechanism of action of the tachykinin NK2 receptor antagonists, SR 48968 ((S)-N-methyl-N[4-acetylamino-4-phenyl-piperidino)-2-(3,4- dichlorophenyl)butyl]benzmide) and MEN 10,627 (cyclo[Met-Asp-Trp-Phe-Dap-Leu) cyclo (2β-5β)]), was compared in the guinea-pig isolated gallbladder and circular muscle of proximal colon by using neurokinin A and [βAla8]neurokinin A-(4-10) as agonists. The experiments performed with colon were in the presence of the tachykinin NK1 receptor-selective antagonist, (±)-CP-96345 (([2-(diphenylmethyl)-N-[(2-methoxyphenyl]-methyl]-11-azabicyclo[2,2,2]octan-3-amine]) SR 48968 caused an insurmountable antagonism of tachykinin NK2 receptor-mediated contraction in both preparations; its blockade was essentially irreversible, since it was not reversed by washout (up to 2 h) and was increased by prolonging the incubation from 15 to 120 min. In contrast, MEN 10,627 produced simple competitive antagonism, which was time-independent and fully reversible in both preparations. In both preparations, the simultaneous administration of SR 48968 and MEN 10,627 produced an intermediate antagonism of the responses to the agonists, as compared to the antagonism produced by each antagonist alone. The present results are discussed in the light of the reported interaction of SR 48968 with tachykinin NK2 receptors at a recognition epitope distinct from that of agonist(s
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