Tail Weight Research Articles

Efficient inference about the tail weight in multivariate Student [formula omitted] distributions

We propose a new testing procedure about the tail weight parameter of multivariate Student t distributions by having recourse to the Le Cam methodology. Our test is asymptotically as efficient as the classical likelihood ratio test, but outperforms the latter by its flexibility and simplicity: indeed, our approach allows to estimate the location and scatter nuisance parameters by any root-n consistent estimators, hereby avoiding numerically complex maximum likelihood estimation. The finite-sample properties of our test are analyzed in a Monte Carlo simulation study, and we apply our method on a financial data set. We conclude the paper by indicating how to use this framework for efficient point estimation.

Alternative way to characterize a [formula omitted]-Gaussian distribution by a robust heavy tail measurement

The q-Gaussians are a class of stable distributions which are present in many scientific fields, and that behave as heavy tailed distributions for aspecific range of q values. The identification of these values, which are used in the description of systems, is sometimes a hard task. In this work the identification of a q-Gaussian distribution from empirical data was done by a measure of its tail weight using robust statistics. Numerical methods were used to generate artificial data, to find out the tail weight — medcouple, and also to adjust the curve between medcouple and the q value. We showed that the medcouple value remains unchanged when the calculation is applied to data which have long memory. A routine was made to calculate the q value and its standard deviation, when applied to empirical data. It is possible to identify a q-Gaussian by the proposed methods with higher precision than in the literature for the same data sample, or as precise as found in the literature. However, in this case, it is required a smaller sample of data. We hope that this method will be able to open new ways for identifying physical phenomena that belongs to nonextensive frameworks.

Compressive behaviour of fibre-reinforced cemented paste backfill

Reinforcement of cemented paste backfill (CPB) with polypropylene fibres was investigated as a way of improving the stability of backfilled underground mine stopes. A series of unconfined compressive strength (UCS) tests were carried out on both non-reinforced and fibre-reinforced cemented tailings. Sandy silt tailings from a nickel mine in Western Australia were used in the study. Ordinary Portland cement at concentrations of 3–5% by weight of tailings and 0–0.5% Adfil-Ignis polypropylene fibres by weight of total solids were used for specimen preparation. The stress–strain curves from the UCS tests showed the inclusion of fibres increased the UCS and significantly reduced the post peak strength loss. Accordingly, the fibre-reinforced specimens were found to be much more ductile than unreinforced specimens, which is highly desirable in many backfill applications. Sliced images acquired from X-ray computed tomography (CT-scan) demonstrated that the observed ductile behaviour of reinforced specimens could be explained by the restraint to crack growth provided by the mobilised fibre tensile strength. At large strains, fibre-reinforced specimens had virtually zero dislodged fragments and retained their integrity as shown in both experimental photos and CT sliced images. This was different from unreinforced specimens, which developed large, wide cracks that resulted in fracturing of the tested specimens. The potential for improving the self-supporting capacity of the fill mass using fibre reinforcing but less cement is discussed and potential advantages, such as reduced ore dilution when excavating adjacent stopes are discussed.

Tail Parameters of Stable Distributions Using One Million Observations of Real Estate Returns from Five Continents

This study focuses on global real estate return distributions. For our analysis, we employ the class of stable distributions that has become prominent in the real estate literature. We add to the literature by undertaking a global-scale analysis for the first time. By using data since the early 1990s, we show that there is considerable variation in the tail weights of return distributions, both between countries as well as among sectors within the countries. It is important to note that the tail parameters vary over time as well. Our results strengthen the notion of non-constant tail parameters in stable distributions that followed earlier findings of constant tail parameters. In addition, our results provide evidence that it is merely the time horizon that causes variation in parameters, than purely methodological differences.

Growth performance and carcass characteristics of weaned rabbits fed varying levels of unfermented and lye digested\fermented cocoa pod husk meal (CPHM)

The study evaluated the growth performance and carcass characteristics of weaned rabbits fed varying levels of undigested/unfermented and lye digested/fermented cocoa pod husk meal in different diets as a source of fibre. A Completely Randomised Design (CRD) was used which comprised of forty unsexed weaned New Zealand and Chinchilla cross rabbits which were randomly allotted into five treatments A, B, C, D and E. Each treatment consisted of eight replicates. Treatment A served as the control diet (without CPHM), B and C had 30% and 40% unfermented CPHM while D and E contained 30% and 40% lye digested\fermented CPHM respectively. Freshly broken cocoa pod husk were collected from a fermentary unit of the Cocoa Research Institute of Nigeria (CRIN) and processed. A known quantity was sundried into a constant weight before milling while the other part was soaked in lye water for one hundred and twenty hours (digested/fermented) i.e five days before being sun dried into a constant weight and milled. The milled unfermented and digested/fermented CPHM were incorporated into the experimental diets at 30% and 40% inclusion levels. The study showed that rabbits fed Diets D and E had significantly (p<0.05) higher body weight gain, feed intake, water consumption and Feed Conversion Ratio (FCR) than those fed diets B,C and A. Rabbits in A (the Control) scored lowest in all the parameters. The carcass analysis also showed that the eviscerated weight, hind limbs, fore-limbs, back and tail weight of rabbits on diets D and E were significantly higher in weight (p<0.05) than those on diets A, B and C. There was no death attributable to CPHM in the diet, therefore, fermented CPHM is recommended as fibre inclusion in rabbit diet in the tropics.Key words: Rabbits, Cocoa Pod Husk Meal, Lye, growth performance, carcass characteristics

Evolution of dispersal distance: maternal investment leads to bimodal dispersal kernels.

Since dispersal research has mainly focused on the evolutionary dynamics of dispersal rates, it remains unclear what shape evolutionarily stable dispersal kernels have. Yet, detailed knowledge about dispersal kernels, quantifying the statistical distribution of dispersal distances, is of pivotal importance for understanding biogeographic diversity, predicting species invasions, and explaining range shifts. We therefore examine the evolution of dispersal kernels in an individual-based model of a population of sessile organisms, such as trees or corals. Specifically, we analyze the influence of three potentially important factors on the shape of dispersal kernels: distance-dependent competition, distance-dependent dispersal costs, and maternal investment reducing an offspring׳s dispersal costs through a trade-off with maternal fecundity. We find that without maternal investment, competition and dispersal costs lead to unimodal kernels, with increasing dispersal costs reducing the kernel׳s width and tail weight. Unexpectedly, maternal investment inverts this effect: kernels become bimodal at high dispersal costs. This increases a kernel׳s width and tail weight, and thus the fraction of long-distance dispersers, at the expense of simultaneously increasing the fraction of non-dispersers. We demonstrate the qualitative robustness of our results against variations in the tested parameter combinations.

Economies of extremes: Lessons from venture-capital decision making

An organization's ability to exploit extreme events—such as exceptional opportunities—depends on its capacity strategy. The venture capital industry illustrates the interplay of expensive capacity and negative externalities from high utilization. The cost of adding a venture capitalist provides a strong incentive to run lean, but such leanness may make it impossible to evaluate all interesting investment opportunities. Using concepts from extreme-value theory, we analyze the trade-off between the costs and benefits arising from an increase in the number of evaluated deals. We ground our analysis in 11 years of archival data from a venture capital firm, representing 3631 deals, the decisions made, the reasons for those decisions, and the decision lead times. The firm identified 20% of arriving deals as worth evaluating during the screening process, but was not able to evaluate approximately 9% of those interesting deals due to a lack of capacity. We show that the value of increasing the number of deals evaluated increases with the tail weight of the distribution of deal values. When the right tail is light, increasing the number of deals evaluated may provide too modest a benefit to justify the cost. When, however, the right tail is heavy, the value of increasing the number of deals is likely to more than compensate for the cost of capacity. Our results provide new insight into the relative value of a chase capacity strategy that emphasizes responsiveness versus a high-utilization heuristic that emphasizes productivity. Our approach can be applied to other search operations such as personnel selection, quality circles seeking to identify root causes, and making employee capacity available for innovation.

Modeling Extreme Events: Sample Fraction Adaptive Choice in Parameter Estimation

When modeling extreme events, there are a few primordial parameters, among which we refer to the extreme value index (EVI) and the extremal index (EI). Under a framework related to large values, the EVI measures the right tail weight of the underlying distribution and the EI characterizes the degree of local dependence in the extremes of a stationary sequence. Most of the semiparametric estimators of these parameters show the same type of behavior: nice asymptotic properties but a high variance for small values of k, the number of upper order statistics used in the estimation, and a high bias for large values of k. This brings a real need for the choice of k. Choosing some well-known estimators of those two parameters, we revisit the application of a heuristic algorithm for the adaptive choice of k. A simulation study illustrates the performance of the proposed algorithm.

Thermo-mechanical properties and microfabric of fly ash-stabilized gold tailings

This paper studies the changes in thermal conductivity, temperature, and unconfined compressive strength of gold tailings and fly ash mixtures during the curing period of 5 days. The microfabric of the cured mixtures was investigated with mercury intrusion porosimetry (MIP). The mixture samples were prepared at their maximum dry unit weight and optimum moisture content. Effect of adding fly ash to gold tailings (i.e., 0, 20, and 40% of the dry weight of tailings) was examined, and a comparison was made on samples prepared at the same fly ash content by replacing gold tailings with humic acid (i.e., gold tailings and humic acid ratios of 100:0, 90:10, and 80:20 by weight) or by varying pore fluid chemistry (i.e., water and salt solutions of 1M NaCl and CaCl2). The results show that the initial thermal conductivity of the samples is sensitive to the mixture proportion and a declination in the thermal conductivity is observed due to hydration of fly ash and evaporation. Inclusion of fly ash and salts into gold tailings improves the unconfined compressive strength but the presence of humic acid in samples leads to the decrease of the strength. MIP results reveal the pore structure changes associated with the packing states of the samples that reflect the influential factors considered.

A New Family of Distributions: Libby-Novick Beta

We define a family of distributions, named the Libby-Novick beta family of distributions, which includes the classical beta generalized and exponentiated generators. The new family offers much more flexibility for modeling real data than these two generators and the Kumaraswamy family of distributions (Cordeiro \& de Castro, 2011). The extended fa\-mily provides reasonable parametric fits to real data in several areas because the additional shape parameters can control the skewness and kurtosis simultaneously, vary tail weights and provide more entropy for the generated distribution. For any given distribution, we can construct a wider distribution with three additional shape parameters which has much more flexibility than the original one. The family density function is a linear combination of exponentiated densities defined from the same baseline distribution. The proposed family also has tractable mathematical properties including moments, generating function, mean deviations and order statistics. The parameters are estimated by maximum likelihood and the observed information matrix is determined. The importance of the family is very well illustrated. By means of two real data sets we demonstrate that this family can give better fits than those ones using the McDonald, beta generalized and Kumaraswamy generalized classes of distributions.

Construction actuarial model for aggregate loss under exponentiated inverted Weibull distribution

The problem of planning reinsurance policies in property and causality insurance companies and how to estimate the loss reserve play an important role for the results of the insurance company. Also, they have past or present data for number of claims and its amounts which want to use in prediction future claim frequency and claim severity. Many statistical distribution are fitting to find an appropriate distribution to represent our data. In this paper, we introduce a statistical distribution known as Exponentiated Inverted Weibull (EIW) distribution to represent the claim amount and its characteristics for applying it in actuarial studies. Second, we test the tail weight of the distribution and maximum likelihood estimation for its parameters. we present our aggregate loss model under collective risk theory when the claim frequency distribution is Poisson or Negative Binomial distribution. Also, we present how to calculate the reinsurance pure premium in case of stop loss reinsurance. Finally, The simulation numerical example is given to represent our results.

Tail Parameters of Stable Distributions Using One Million Observations of Real Estate Returns from Five Continents

This study focuses on global real estate return distributions. For our analysis, we employ the class of stable distributions that has become prominent in the real estate literature. We add to the literature by undertaking a global-scale analysis for the first time. By using data since the early 1990s, we show that there is considerable variation in the tail weights of return distributions, both between countries as well as among sectors within the countries. It is important to note that the tail parameters vary over time as well. Our results strengthen the recently discovered notion about non-constant tail parameters in stable distributions, which contradicts earlier findings about constant tail parameters. Additionally, we argue that merely changes over time were to be discovered, rather than pure methodological facts driving the variation, which is in contrast to the initial assumption associated with constant tail parameters. Our results provide an extensive overview of the tailedness of global real estate markets and offer a comprehensive insight into differing market distributions.

Yield characteristics and morphometric relationships of giant freshwater prawn, Macrobrachium rosenbergii (de Man, 1879)

Meat yield of 233 individuals of giant freshwater prawn, Macrobrachium rosenbergii (de Man, 1879), and their morphometric relationships were examined. Morphometric parameters of different length and weight measurements were recorded for both the sexes separately and subjected to analysis. The meat yield of prawns was size and sex dependent with females showing significantly greater (P < 0.05) tail meat yield than males. The tail meat as a body weight percentage ranges from 26.12 to 40.75 and 32.97 to 42.11 in males and females, respectively. Much of the differences in yield are related to the size and weight of the head and claws. The head weight of males was observed to be higher compared to females in all the size classes. Regression slopes of total length versus body weight and total length versus head weight were significantly higher than critical isometric value indicating high positive allometric growth in both the sexes, with males showing significantly higher (P < 0.05) slope than females. The relationship parameters of total length versus tail weight and total length versus tail meat showed a positive allometric growth in females, whereas it is isometry and negative allometry in males. The morphometric relationship of tail length versus all weight measurements showed positive allometry and negative allometry in females and males, respectively.

The Influence of Synaptic Weight Distribution on Neuronal Population Dynamics

The manner in which different distributions of synaptic weights onto cortical neurons shape their spiking activity remains open. To characterize a homogeneous neuronal population, we use the master equation for generalized leaky integrate-and-fire neurons with shot-noise synapses. We develop fast semi-analytic numerical methods to solve this equation for either current or conductance synapses, with and without synaptic depression. We show that its solutions match simulations of equivalent neuronal networks better than those of the Fokker-Planck equation and we compute bounds on the network response to non-instantaneous synapses. We apply these methods to study different synaptic weight distributions in feed-forward networks. We characterize the synaptic amplitude distributions using a set of measures, called tail weight numbers, designed to quantify the preponderance of very strong synapses. Even if synaptic amplitude distributions are equated for both the total current and average synaptic weight, distributions with sparse but strong synapses produce higher responses for small inputs, leading to a larger operating range. Furthermore, despite their small number, such synapses enable the network to respond faster and with more stability in the face of external fluctuations.

Modeling meat yield based on measurements of body traits in genetically improved giant freshwater prawn (GFP) Macrobrachium rosenbergii

A single-generation dataset consisting of 1,730 records from a selection program for high growth rate in giant freshwater prawn (GFP, Macrobrachium rosenbergii) was used to derive prediction equations for meat weight and meat yield. Models were based on body traits [body weight, total length and abdominal width (AW)] and carcass measurements (tail weight and exoskeleton-off weight). Lengths and width were adjusted for the systematic effects of selection line, male morphotypes and female reproductive status, and for the covariables of age at slaughter within sex and body weight. Body and meat weights adjusted for the same effects (except body weight) were used to calculate meat yield (expressed as percentage of tail weight/body weight and exoskeleton-off weight/body weight). The edible meat weight and yield in this GFP population ranged from 12 to 15 g and 37 to 45 %, respectively. The simple (Pearson) correlation coefficients between body traits (body weight, total length and AW) and meat weight were moderate to very high and positive (0.75–0.94), but the correlations between body traits and meat yield were negative (−0.47 to −0.74). There were strong linear positive relationships between measurements of body traits and meat weight, whereas relationships of body traits with meat yield were moderate and negative. Step-wise multiple regression analysis showed that the best model to predict meat weight included all body traits, with a coefficient of determination (R 2) of 0.99 and a correlation between observed and predicted values of meat weight of 0.99. The corresponding figures for meat yield were 0.91 and 0.95, respectively. Body weight or length was the best predictor of meat weight, explaining 91–94 % of observed variance when it was fitted alone in the model. By contrast, tail width explained a lower proportion (69–82 %) of total variance in the single trait models. It is concluded that in practical breeding programs, improvement of meat weight can be easily made through indirect selection for body trait combinations. The improvement of meat yield, albeit being more difficult, is possible by genetic means, with 91 % of the variation in the trait explained by the body and carcass traits examined in this study.

Determining the effect of the fat-tail and carcass weight on meat fatty acid composition of Iranian lambs

Fat-tailed sheep are widely distributed around the globe, probably because of their ability to adapt and endure harsh environmental conditions. Climate change and increasing demand for protein mean these animals are a vital part of our food chain. Despite this, little is known about the composition of their meat. The aim of our study was to investigate the effect of the fat-tail and carcass weight on chemical composition and fatty acid profile of Longissimus dorsi muscle of lambs. We compared sixty male lambs from three fat-tail weight classes (tailed, light fat-tailed, heavy fat-tailed) and two carcass weight ranges (6–13kg, designated light-LC; 13–21kg, designated moderate-MC). These lambs were randomly selected from a local flock grazed under standard commercial conditions in Mazandran, Iran. Our results showed that heavy fat-tailed (HF) lambs deposit less intramuscular fat than light fat tailed (LF) and tailed (T) lambs (p<0.05). Lambs with moderate carcasses (MC) weight, deposited more intramuscular fat compared with lambs which had low carcass weight (p<0.001). Polyunsaturated fatty acids (PUFA) are considered healthier than saturated fatty acids (SFA). LC lambs had higher PUFA:SFA and lower n-6:n-3PUFA ratio (p<0.001), than MC lambs. There were no significant differences in the fatty acid profile of lambs due to the different fat tail weights. In conclusion, lambs with higher carcasses weight and intramuscular fat, had higher levels of unfavorable fatty acids. However, changes in intramuscular fat did not affect the fatty acid profile of lambs with different tail weights.

The beta generalized logistic distribution

For the first time, a four-parameter beta generalized logistic distribution is obtained by compounding the beta and generalized logistic distributions. The new model extends some well-known distributions and its shape is quite flexible, specially the skewness and the tail weights, due to the extra shape parameters. We obtain general expansions for the moment generating and quantile functions. The estimation of the parameters is investigated by maximum likelihood. An application to a real data set is given to show the flexibility and potentiality of our distribution.

Tail Parameters of Stable Distributions Using One Million Observations of Real Estate Returns from Five Continents

This study focuses on global real estate return distributions. For our analysis, we employ the class of stable distributions that has become prominent in the real estate literature. We add to the literature by undertaking a global-scale analysis for the first time. By using data since the early 1990s, we show that there is considerable variation in the tail weights of return distributions, both between countries as well as among sectors within the countries. It is important to note that the tail parameters vary over time as well. Our results strengthen the recently discovered notion about non-constant tail parameters in stable distributions, which contradicts earlier findings about constant tail parameters. Additionally, we argue that merely changes over time were to be discovered, rather than pure methodological facts driving the variation, which is in contrast to the initial assumption associated with constant tail parameters. Our results provide an extensive overview of the tailedness of global real estate markets and offer a comprehensive insight into differing market distributions.

Beta generalized normal distribution with an application for SAR image processing

In this paper, we introduce the beta generalized normal distribution, which is obtained by compounding the beta and generalized normal [S. Nadarajah, A generalized normal distribution, J. Appl. Stat. 32 (2005), pp. 685–694] distributions. The new model includes as sub-models the beta normal, beta Laplace, normal, and Laplace distributions. The shape of the new distribution is quite flexible, especially skewness and tail weights, due to two additional parameters. We obtain general expansions for the moments. We investigate the estimation of the parameters by maximum likelihood. We also propose a random number generator for the new distribution. We analyse and model actual synthetic aperture radars after the new distribution. The results could outperform the 0, Κ, and Γ distributions in several scenarios.

Log-gamma-generated families of distributions

We introduce two new general families of continuous distributions, generated by a distribution F and two positive real parameters α and β which control the skewness and tail weight of the distribution. The construction is motivated by the distribution of k-record statistics and can be derived by applying the inverse probability integral transformation to the log-gamma distribution. The introduced families are suitable for modelling the data with a significantly skewed and heavy-tailed distribution. Various properties of the introduced families are studied and a number of estimations and data fitness on real data are given to illustrate the results.