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Regression Framework (regression + framework)
Selected AbstractsPhylogenetic Comparative Methods Strengthen Evidence for Reduced Genetic Diversity among Endangered TetrapodsCONSERVATION BIOLOGY, Issue 5 2010PATRICK A. FLIGHT evolución de la historia de vida; extinción; heterocigosidad de proteínas; regresión filogenética; tamaño poblacional efectivo Abstract:,The fitness of species with little genetic diversity is expected to be affected by inbreeding and an inability to respond to environmental change. Conservation theory suggests that endangered species will generally demonstrate lower genetic diversity than taxa that are not threatened. This hypothesis has been challenged because the time frame of anthropogenic extinction may be too fast to expect genetic factors to significantly contribute. I conducted a meta-analysis to examine how genetic diversity in 894 tetrapods correlates with extinction threat level. Because species are not evolutionarily independent, I used a phylogenetic regression framework to address this issue. Mean genetic diversity of tetrapods, as assessed by protein heterozygosity, was 29.7,31.5% lower on average in threatened species than in their nonthreatened relatives, a highly significant reduction. Within amphibians as diversity decreased extinction risk increased in phylogenetic models, but not in nonphylogenetic regressions. The effects of threatened status on diversity also remained significant after accounting for body size in mammals. These results support the hypothesis that genetic effects on population fitness are important in the extinction process. Resumen:,Se espera que la adaptabilidad de una especie con poca diversidad genética sea afectada por la endogamia y una incapacidad para responder a cambios ambientales. La teoría de la conservación sugiere que las especies en peligro generalmente muestran menor diversidad genética que taxa que no están amenazados. Esta hipótesis ha sido cuestionada porque el período de tiempo de la extinción antropogénica puede ser muy rápido para esperar que los factores genéticos contribuyan significativamente. Realice un meta-análisis para examinar cómo se correlaciona la diversidad genética de 894 tetrápodos con el nivel de amenaza de extinción. Debido a que las especies no son independientes evolutivamente, utilice un marco de regresión filogenética para abordar este tema. La media de la diversidad genética de tetrápodos, medida como la heterocigosidad de proteínas, fue 29.7,31.5% menor en las especies amenazadas que en sus parientes no amenazados, una reducción altamente significativa. En anfibios, a medida que disminuía la diversidad el riesgo de extinción incrementaba en los modelos filogenéticos, pero no en las regresiones no filogenéticas. El efecto del estatus de amenaza sobre la biodiversidad también permaneció significativo después de considerar el tamaño corporal de mamíferos. Estos resultados dan soporte a la hipótesis de que los efectos genéticos sobre la adaptabilidad de la población son importantes en el proceso de extinción. [source] Trade Liberalization and the Fiscal Squeeze: Implications for Public InvestmentDEVELOPMENT AND CHANGE, Issue 3 2003Barsha Khattry This article examines the impact of trade liberalization on the level and structure of government expenditures across countries, with particular emphasis on low income countries. It develops the argument that the policies employed during trade liberalization have resulted in a fiscal squeeze as a result of declining tax revenues and rising interest expenditures. To surmount this fiscal hurdle, expenditures on physical capital, which have negligible political ramifications, have been reduced. Other more politically sensitive expenditures, such as spending on social capital, have been financed by incurring additional debt. However, additional debt has exerted upward pressure on interest payments, further exacerbating the fiscal situation. The statistical analysis carried out to examine the evidence uses panel data for eighty developing and industrialized countries over the period 1970,98 and employs a fixed,effects regression framework to account for country,specific characteristics. The results indicate that trade liberalization has indeed resulted in declining revenues and higher interest expenditures and that these factors have contributed to the observed decline in infrastructure spending. [source] Combining spatial and phylogenetic eigenvector filtering in trait analysisGLOBAL ECOLOGY, Issue 6 2009Ingolf Kühn ABSTRACT Aim, To analyse the effects of simultaneously using spatial and phylogenetic information in removing spatial autocorrelation of residuals within a multiple regression framework of trait analysis. Location, Switzerland, Europe. Methods, We used an eigenvector filtering approach to analyse the relationship between spatial distribution of a trait (flowering phenology) and environmental covariates in a multiple regression framework. Eigenvector filters were calculated from ordinations of distance matrices. Distance matrices were either based on pure spatial information, pure phylogenetic information or spatially structured phylogenetic information. In the multiple regression, those filters were selected which best reduced Moran's I coefficient of residual autocorrelation. These were added as covariates to a regression model of environmental variables explaining trait distribution. Results, The simultaneous provision of spatial and phylogenetic information was effectively able to remove residual autocorrelation in the analysis. Adding phylogenetic information was superior to adding purely spatial information. Applying filters showed altered results, i.e. different environmental predictors were seen to be significant. Nevertheless, mean annual temperature and calcareous substrate remained the most important predictors to explain the onset of flowering in Switzerland; namely, the warmer the temperature and the more calcareous the substrate, the earlier the onset of flowering. A sequential approach, i.e. first removing the phylogenetic signal from traits and then applying a spatial analysis, did not provide more information or yield less autocorrelation than simple or purely spatial models. Main conclusions, The combination of spatial and spatio-phylogenetic information is recommended in the analysis of trait distribution data in a multiple regression framework. This approach is an efficient means for reducing residual autocorrelation and for testing the robustness of results, including the indication of incomplete parameterizations, and can facilitate ecological interpretation. [source] Immigrants and the use of preventive care in the United States,HEALTH ECONOMICS, Issue 7 2009Yuriy Pylypchuk Abstract Using data from the Medical Expenditure Panel Survey, we compare immigrants' use of preventive care with that of natives. We employ a multinomial switching regression framework that accounts for non-random selection into continuous private insurance, temporary private insurance, public insurance, and no insurance. Our results indicate that among the populations with continuous private coverage and without coverage (uninsured), immigrants, especially non-citizens, are less likely to use preventive care than natives. We find that the longer immigrants stay in the US the more their use of care approximates to that of natives. However, for most types of care, immigrants' use of care never fully converges to that of natives. Among the publicly insured population, immigrants' use of care is similar to natives, but non-citizen immigrants are significantly less likely to use preventive measures. We find that the ability to speak English does not have a significant effect on the use of preventive care among publicly insured persons. Published in 2008 by John Wiley & Sons, Ltd. [source] Venture Creation Speed and Subsequent Growth: Evidence from South AmericaJOURNAL OF SMALL BUSINESS MANAGEMENT, Issue 3 2010Joan-Lluis Capelleras Though time is an important dimension of the venture creation process, our understanding of why some entrepreneurs are able to act more quickly than others is limited. Equally, not much is known about the relationship between venture creation speed and the subsequent venture growth. In this paper, we use a resource-based perspective to provide insights into the factors that quicken or retard venture creation and to explore how speed impacts on subsequent growth. This is important because the topic remains generally underresearched and because even less is understood about venture creation speed in the context of South American economies. Data were collected from face-to-face interviews with 647 entrepreneurs in Argentina, Brazil, Chile, and Peru. Using a multivariate regression framework, we find that entrepreneurs make use of their human and social capital resources to shape the speed by which their venture is created. Moreover, their perceptions of unfavorable environmental conditions seem to retard venture creation. Findings also suggest that entrepreneurs who take more time to create a more solid resource base tend to receive better growth outcomes. Implications from the findings are discussed. [source] Glass Ceiling or Sticky Floor?THE ECONOMIC RECORD, Issue 259 2006Exploring the Australian Gender Pay Gap Using the Household, Income and Labour Dynamics in Australia survey, this paper analyses the gender wage gaps across the wage distribution in both the public and private sectors in Australia. Quantile regression techniques are used to control for various characteristics at different points of the wage distributions. Counterfactual decomposition analysis, adjusted for the quantile regression framework, is used to examine if the gap is attributed to gender differences in characteristics, or to the differing returns between genders. The main finding is that a strong glass ceiling effect is detected only in the private sector. A second finding is that the acceleration in the gender gap across the distribution does not vanish even after account is taken of an extensive set of statistical controls. This suggests that the observed wage gap is a result of differences in returns to genders. By focusing only on the mean gender wage gap, substantial variations of the gap will be hidden. [source] A Regression-based Association Test for Case-control Studies that Uses Inferred Ancestral Haplotype SimilarityANNALS OF HUMAN GENETICS, Issue 5 2009Youfang Liu Summary Association methods based on haplotype similarity (HS) can overcome power and stability issues encountered in standard haplotype analyses. Current HS methods can be generally classified into evolutionary and two-sample approaches. We propose a new regression-based HS association method for case-control studies that incorporates covariate information and combines the advantages of the two classes of approaches by using inferred ancestral haplotypes. We first estimate the ancestral haplotypes of case individuals and then, for each individual, an ancestral-haplotype-based similarity score is computed by comparing that individual's observed genotype with the estimated ancestral haplotypes. Trait values are then regressed on the similarity scores. Covariates can easily be incorporated into this regression framework. To account for the bias in the raw p-values due to the use of case data in constructing ancestral haplotypes, as well as to account for variation in ancestral haplotype estimation, a permutation procedure is adopted to obtain empirical p-values. Compared with the standard haplotype score test and the multilocus T2 test, our method improves power when neither the allele frequency nor linkage disequilibrium between the disease locus and its neighboring SNPs is too low and is comparable in other scenarios. We applied our method to the Genetic Analysis Workshop 15 simulated SNP data and successfully pinpointed a stretch of SNPs that covers the fine-scale region where the causal locus is located. [source] Exchange rate uncertainty and employment: an algorithm describing ,play'APPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 2 2001Ansgar Belke Abstract The paper deals with the impacts of exchange rate uncertainty on the relationship between macroeconomic labour market variables. Under uncertainty, areas of weak reactions,so-called ,play' areas,have to be considered at the macrolevel. The width of the play area is a positive function of the degree of uncertainty. When changes go beyond the play-area suddenly strong reactions (,spurts') occur. These non-linear dynamics are captured in a simplified linearized way. An algorithm describing linear play hysteresis is developed and implemented into a regression framework. As an empirical application, the exchange rate impacts on German employment are analysed considering play effects. Copyright © 2001 John Wiley & Sons, Ltd. [source] Reevaluation of the interaction between HLA,DRB1 shared epitope alleles, PTPN22, and smoking in determining susceptibility to autoantibody-positive and autoantibody-negative rheumatoid arthritis in a large UK Caucasian populationARTHRITIS & RHEUMATISM, Issue 9 2009Ann W. Morgan Objective To define interactions between the HLA,DRB1 shared epitope (SE), PTPN22, and smoking in cyclic citrullinated peptide (CCP) antibody, and rheumatoid factor (RF),positive and ,negative rheumatoid arthritis (RA). Methods Data on ,5,000 RA patients and ,3,700 healthy controls recruited from 6 centers in the UK were analyzed; not all centers had both genotype data and smoking data available for study. The magnitude of association was assessed in autoantibody-positive and -negative subgroups. The effect of smoking on antibody status among cases was assessed following adjustment for year of birth and center, using Mantel-Haenszel analysis. Analyses of the combined effects of PTPN22, HLA,DRB1 SE, and smoking were performed using additive and multiplicative models of interaction within a logistic regression framework. Results The combined effects of PTPN22, HLA,DRB1 SE, and smoking were defined, with no evidence of departure from a multiplicative model. Within the case population, all 3 factors were independently associated with the generation of CCP antibodies (odds ratio [OR] 11.1, P < 0.0001), whereas only HLA,DRB1 SE and smoking were independently associated with RF production (OR 4.4, P < 0.0001). There was some evidence of increasing likelihood of antibody positivity with heavier smoking. Finally, we demonstrated that smoking was associated with the generation of both CCP and RF antibodies (OR 1.7, P = 0.0001). Conclusion PTPN22 appears to be primarily associated with anticitrulline autoimmunity, whereas HLA,DRB1 SE is independently associated with RF. This study has confirmed associations of specific gene,environment combinations with a substantially increased risk of developing RA. Further work is needed to determine how these data can be used to inform clinical practice. [source] On Gene Ranking Using Replicated Microarray Time Course DataBIOMETRICS, Issue 1 2009Yu Chuan Tai Summary Consider the ranking of genes using data from replicated microarray time course experiments, where there are multiple biological conditions, and the genes of interest are those whose temporal profiles differ across conditions. We derive a multisample multivariate empirical Bayes' statistic for ranking genes in the order of differential expression, from both longitudinal and cross-sectional replicated developmental microarray time course data. Our longitudinal multisample model assumes that time course replicates are independent and identically distributed multivariate normal vectors. On the other hand, we construct a cross-sectional model using a normal regression framework with any appropriate basis for the design matrices. In both cases, we use natural conjugate priors in our empirical Bayes' setting which guarantee closed form solutions for the posterior odds. The simulations and two case studies using published worm and mouse microarray time course datasets indicate that the proposed approaches perform satisfactorily. [source] European Enlargement and Agro-Food TradeCANADIAN JOURNAL OF AGRICULTURAL ECONOMICS, Issue 4 2008tefan Bojnec This paper investigates the level, composition, and differences in the dynamics of revealed comparative advantage and trade specialization patterns of the 12 new member states (NMS-12) as part of the enlarged European Union 27 countries (EU-27). The NMS-12 are classified into four country groups: the Baltic States, the CEFTA-5, and the Mediterranean and the Balkan regions. The empirical analysis employs a regression framework, a duration analysis, Markov transition probability matrices, and mobility indices. Trade increases with the EU enlargement and so does revealed comparative advantage in agro-food products. There are catching-up difficulties, as indicated by revealed comparative advantage, in higher added-value processed products. Le présent article examine le degré, la composition et les différences de la dynamique des avantages comparatifs révélés ainsi que les caractéristiques de la spécialisation du commerce des douze nouveaux pays membres (NPM-12) de l'Union européenne élargie (UE,27). Les 12 nouveaux pays membres sont divisés en quatre groupes: les États baltiques, les cinq pays membres de l'ALECE, la région de la Méditerranée et la région des Balkans. L'analyse empirique utilise un modèle de régression, une analyse de durée, des matrices de probabilités des transitions (Markov) et des indices de mobilité. Les échanges augmentent avec l'élargissement de l'UE tout comme les avantages comparatifs révélés des produits agroalimentaires. On observe des difficultés de rattrapage, comme l'indique l'avantage comparatif révélé, dans le cas des produits transformés à forte valeur ajoutée. [source] | |||||||||||||||||||