João Domingos Scalon

State-space algorithms for estimating spike rate functions

The accurate characterization of spike firing rates including the determination of when changes in activity occur is a fundamental issue in the analysis of neurophysiological data. Here we describe a state-space model for estimating the spike rate function that provides a maximum likelihood estimate of the spike rate, model goodness-of-fit assessments, as well as confidence intervals for the spike rate function and any other associated quantities of interest. Using simulated spike data, we first compare the performance of the state-space approach with that of Bayesian adaptive regression splines (BARS) and a simple cubic spline smoothing algorithm. We show that the state-space model is computationally efficient and comparable with other spline approaches. Our results suggest both a theoretically sound and practical approach for estimating spike rate functions that is applicable to a wide range of neurophysiological data.

Using Generalized Mantel-Haenszel Statistics to Assess DIF Among Multiple Groups

In spite of the growing interest in cross-cultural research and assessment, there is little research on statistical procedures that can be used to simultaneously assess the differential item functioning (DIF) across multiple groups. The chief objective of this work is to show a unified framework for the analysis of DIF in multiple groups using one of the most popular methodologies for DIF assessment: the Mantel-Haenszel (MH) methods. The MH statistics proposed to date with this purpose only permitted analysis of the DIF for dichotomous items. In contrast, the statistics presented here permit, through a single significance test, simultaneous evaluation of the DIF in several groups, being applicable to both dichotomous and polytomous items. Specific software to detect DIF using this methodology is available free of charge.

Spatial and temporal dynamics of coffee-leaf-miner and predatory wasps in organic coffee field in formation

The coffee production is an economic mainstay for many countries in the world. Brazil is the world’s largest producer and exporter of coffee, being responsible for about 25% of the world production. It is well known that coffee plantations are susceptible to more than 850 fungal and insect pests. Among these pests, the most important significant throughout Brazil is the coffee-leaf-miner, [Leucoptera coffeella (Guerin-Meneville & Perrottet, 1842) (Lepidoptera: Lyonetiidae)]. It is estimated that the loss in yield due to infestation by L. coffeella moths can increase to as much as 80% in areas where the coffee-leaf-miner larvae are not controlled. Though it is effective, the chemical control of the pest substantially increases the cost of production and constitutes a risk to the environment. The knowledge about the spatialtemporal dynamics of coffee-leaf-miner and predatory wasps may provide valuable information about the biological management pest context. One way to investigate the spatialtemporal synchronism of predator and prey is to calculate and compare an index of spatial randomness within a sequence time. This paper advocates using the Morisita’s index, coupled with the bootstrap method, in a temporal sequence to characterize the spatial- temporal dynamics of coffee-leaf-miner and predatory wasp (Hymenoptera: Vespidae) in one hectare of an organic coffee plantation. The results showed that coffeeleaf-miner and predatory wasps presented a seasonal behavior with a temporal synchronism. The results also showed that both new and preyed mines were aggregated during the peak population (dry season). There was little evidence for spacetime interaction between coffee-leaf-miner and predatory wasps.

Parameters estimation in the model for in situ degradability of mertens and loften

Objetiva-se avaliar o comportamento dos parâmetros do modelo de degradacao proposto por Mertens & Loften (1980) ajustado aos resultados de um ensaio de degradabilidade in situ. No experimento e avaliado o residuo potencialmente degradavel da fibra em detergente neutro (FDN) da graminea coastcross (Cynodon dactylon x Cynodon nlemfunensis) cortada aos 60 dias, com tres repeticoes. O residuo potencialmente degradavel da FDN e estudado utilizando quinze tempos de incubacao (0; 0,5; 1; 3; 6; 9; 12; 18; 24; 36; 48; 56; 72; 96 e 120 horas). A parcela experimental e constituida por uma vaca nao lactante, com fistula ruminal permanente. Sao obtidos ajustes medios e individuais para os animais. Obtem-se tambem as variâncias dos estimadores dos parâmetros por meio da matriz de variância e covariância dos parâmetros e pelo metodo jackknife, propondo-se expressoes para a estimacao do intervalo de confianca para os parâmetros do modelo. Os resultados mostram que o metodo de jackknife apresenta maior estimativa de variância para os parâmetros do modelo de Mertens & Loften (1980), resultando em intervalos de confianca de maior amplitude e estimativas dos parâmetros menos precisas, nos ajustes individuais e medios.

EQUAÇÕES HIPSOMÉTRICAS PARA Eucalyptus spp. NÃO MANEJADO EM IDADE AVANÇADA COM TÉCNICAS DE INCLUSÃO DE COVARIANTES

The aim of the study was to establish hypsometric equations for unmanaged Eucalyptus spp. in old age. For this purpose we measured the diameter and height of 513 stems distributed in 11 species and the hypsometric relationship was established by six regression models, being selected the one with the best Akaike Information Criterion (AIC), standard error of estimative (Syx), Maximum Likelihood Ratio Test and Residual Graphical Analysis. Subsequently, the best model has undergone the inclusion of the covariates stem quality (Qf) and Species (Sp) by means of the decomposition of its parameters. Under these conditions, the model of Chapman and Richards showed the best performance in both modeling approaches. When compared both models, we observed a reduction of 71 AIC units and 7.4% in Syx and a significant improvement in all aspects of the residual distribution in the model with covariates. The results show that it is possible to provide hypsometric equations suitable for unmanaged Eucalyptus in old age, with and without addition of covariates, and the last technique has provided significant improvement in the quality of fit of the models.

Use of the correlation coefficient between plots in order to improve the accuracy of forest inventories

Forest inventories are usually compiled without taking into account the existing correlations between sampling units, which is debatable particularly where the calculations involve environmental variables. When the potential correlations between sampling units are overlooked, the accuracy of such inventories becomes distorted in terms of the confidence interval range for the variable of interest, which is volume in cubic meters. The magnitude and form of such distortion will vary according to the correlation intensity between sampling units. This study aimed to present an analysis of the addition of the correlation coefficient to the calculation of the variance of the mean in a systematic sampling procedure of a native forest population or area, as well as its impact on the accuracy of the resulting estimates, with the assumption of independence between sampling units and with the addition of a correlation between sampling units as suggested by Cochran. Results revealed that, where the correlation coefficient was added to the variance of the mean formula, it increased inventory accuracy by about 14.3%, leading to the conclusion that such an effect will occur in any forest inventory being compiled for any forest population or area of interest.

Análise espacial de um fragmento florestal baseada no mosaico de dirichlet

The spatial pattern of trees affects a large number of physiological and ecological processes in a forest, including competition, distribution, size, growth and mortality of the species. Methods based on the Ripleys K function have been frequently used to characterize the spatial configuration of a forest. In this article we advocate to use methods that are based on areas of the Dirichlets mosaic (function D) to describe the spatial distribution of trees. Due to the importance of Xylopia brasiliensis (Pindaiba) in the structure and dynamics of Semideciduous montana forests, this study assessed the K and D functions to describe the spatial distribution of this specie. Results showed that the estimators of the K and D functions, combined with Monte Carlo simulations, led to rejection of the null hypothessis of completely spatial randomness (p < 0,10 ) of the Xylopia brasiliensis in favor of the presence of clustering of the specie within the forest fragment.

Uso dos métodos Mantel-Haenszel para a detecção do funcionamento diferencial dos itens e software relacionado

Statistics comprised under Mantel-Haenszel (MH) methods designation constitute one of the most popular and low cost differential item functioning (DIF) detection methods. Mantel-Haenszel methods permit DIF assessment of dichotomous and polytomous items in multiple groups simultaneously, and they can be applied both under Classical Test Theory and Item Response Theory. This paper provides a framework for integrating the different MH statistics used in DIF research, and describes the software that has been developed to provide an easy-to-use program for conducting DIF analyses using the statistics. The program is free of charge and it is available in the following languages: Spanish, English and Portuguese.

Spatial Variability of Air Temperature In A Broiler House During The Heating Phase

The air temperature (tair) exerts great influence on the development of poultry during their heating phase. Therefore, the aim of this study was to analyze the structure and the magnitude of the tair spatial variability, using geostatistics tools such as semivariogram analysis and also producing kriging maps. The experiment was conducted in the west mesoregion of Minas Gerais State in 2010, in a commercial broiler house with heating system consisting of two furnaces that heat the air indirectly, in the first 14 days of the birds’ life. It was possible to characterize the variability of the tair, which allowed to observe the spatial dependence by using geostatistics techniques. In addition, the use of geostatistics and distribution maps made possible to identify problems in the heating system in regions inside the broiler house that may harm the development of chicks.

A combined test for randomness of spatial distribution of composite microstructures

A new methodology is presented for characterizing the spatial distribution of second-phase particles in planar sections of multi-phase materials. It is based on the issue of statistically summarizing the results of independent tests against the hypothesis of randomness of the particles. The methodology was applied in multiple planar sections of an aluminium alloy reinforced with silicon carbide particles and leaded to a rejection of the hypothesis of randomness even when the tests from single planar sections were ambiguous.