scholarly journals Stochastic Mixed-Effects Parameters Bertalanffy Process, with Applications to Tree Crown Width Modeling

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Petras Rupšys
Keyword(s):  
Fixed Effects ◽  
Estimation Method ◽  
National Forest Inventory ◽  
Mixed Effects ◽  
Tree Crown ◽  
Crown Width ◽  
Maximum Likelihood Procedure ◽  
Pine Trees ◽  
Performance Statistics ◽  
Technique Comparison

A stochastic modeling approach based on the Bertalanffy law gained interest due to its ability to produce more accurate results than the deterministic approaches. We examine tree crown width dynamic with the Bertalanffy type stochastic differential equation (SDE) and mixed-effects parameters. In this study, we demonstrate how this simple model can be used to calculate predictions of crown width. We propose a parameter estimation method and computational guidelines. The primary goal of the study was to estimate the parameters by considering discrete sampling of the diameter at breast height and crown width and by using maximum likelihood procedure. Performance statistics for the crown width equation include statistical indexes and analysis of residuals. We use data provided by the Lithuanian National Forest Inventory from Scots pine trees to illustrate issues of our modeling technique. Comparison of the predicted crown width values of mixed-effects parameters model with those obtained using fixed-effects parameters model demonstrates the predictive power of the stochastic differential equations model with mixed-effects parameters. All results were implemented in a symbolic algebra system MAPLE.

Generalized fixed-effects and mixed-effects parameters height–diameter models with diffusion processes

2015 ◽  
Vol 08 (05) ◽  
pp. 1550060 ◽  
Author(s):  
Petras Rupšys
Keyword(s):  
Fixed Effects ◽  
Diffusion Processes ◽  
Random Parameter ◽  
Mixed Effects ◽  
Validation Dataset ◽  
Natural Systems ◽  
Breast Height ◽  
Deterministic Function ◽  
Pine Trees ◽  
Soil Fertility Index

Statistical models using stochastic differential equations (SDEs) to describe dynamically evolving natural systems are appearing in the scientific literature with some regularity in recent years. In this study, the SDE mixed-effects parameter models based on a Vasicek non-homogeneous diffusion process are formulated. The breast height diameter-dependent drift function additionally depends on deterministic function that describes the dynamic of certain exogenous stand variables (crown height, c h , crown width, c w , mean breast height diameter, d0, mean height, h0, age, A, soil fertility index, SFI, stocking level, S) versus breast height diameter. The mixed-effects parameters SDE models included a random parameter that affected the models asymptote. The parameter estimators are evaluated by maximum likelihood procedure. The objective of the research was to develop a generalized mixed-effects parameters SDE height–diameter models and to illustrate issues using dataset of Scots pine trees (Pinus sylvestris L.) in Lithuania with the breast height diameter outside the bark larger than 0 cm. The parameters of all used models were estimated using an estimation dataset and were evaluated using a validation dataset. The new developed height–diameter models are an improvement over exogenous stand variables, in that it can be calibrated to a new stand with observed height–diameter pairs, thus improving height prediction.

scholarly journals Analyzing ingrowth using zero-inflated negative binomial models

Silva Fennica ◽  
2020 ◽  
Vol 54 (4) ◽  
Author(s):  
Juha Lappi ◽  
Timo Pukkala
Keyword(s):  
Fixed Effects ◽  
Negative Binomial ◽  
Basal Area ◽  
National Forest Inventory ◽  
Mixed Effects ◽  
Low Fertility ◽  
Mixed Effects Models ◽  
Permanent Sample Plots ◽  
Temperature Sum ◽  
Stand Basal Area

Ingrowth is an important element of stand dynamics in several silvicultural systems, especially in continuous cover forestry. Earlier predictive models for ingrowth in Finnish forests are few and not based on up-to-date statistical methods. Ingrowth is here defined as the number of trees over 1.3 m entering a plot. This study developed new ingrowth models for Scots pine ( L.), (Picea abies (L.) H. Karst.) and birch ( Roth and Ehrh.) using data from the permanent sample plots of the Finnish national forest inventory. The data were over-dispersed compared to a Poisson process and had many zeros. Therefore, a zero-inflated negative binomial model was used. The total and species-specific stand basal areas, temperature sum and fertility class were used as predictors in the ingrowth models. Both fixed-effects and mixed-effects models were fitted. The mixed-effects model versions included random plot effects. The mixed-effects models had larger likelihoods but provided biased predictions. Also censored prediction was considered where only a certain maximum number of ingrowth trees were accepted for a plot. The models predicted most pine ingrowth in pine-dominated stands on sub-xeric and xeric sites where stand basal area was low. The predicted amount of spruce ingrowth was maximized when the basal area of spruce was 13 m ha. Increasing temperature sum increased spruce ingrowth. Predicted birch ingrowth decreased with increasing stand basal area and towards low fertility classes. An admixture of pine increased the predicted amount of spruce ingrowth.Pinus sylvestrisNorway spruceBetula pendulaB. pubescens2–1

scholarly journals Country of Origin Effects on the Average Annual Values of NHL Player Contracts

2019 ◽  
Vol 7 (2) ◽  
pp. 24
Author(s):  
Aju J. Fenn ◽  
Lucas Gerdes ◽  
Samuel Rothstein
Keyword(s):  
Quantile Regression ◽  
Fixed Effects ◽  
Country Of Origin ◽  
Large Datasets ◽  
National Hockey League ◽  
Dummy Variables ◽  
Country Of Origin Effects ◽  
Performance Statistics ◽  
Career Performance ◽  
Using Data

Using data from 2005 to 2016, this paper examines if players in the National Hockey League (NHL) are being paid a positive differential for their services due to the competition from the Kontinental Hockey League (KHL) and the Swedish Hockey League (SHL). In order to control for performance, we use two different large datasets, (N = 4046) and (N = 1717). In keeping with the existing literature, we use lagged performance statistics and dummy variables to control for the type of NHL contract. The first dataset contains lagged career performance statistics, while the performance statistics are based on the statistics generated during the years under the player’s previous contract. Fixed effects least squares (FELS) and quantile regression results suggest that player production statistics, contract status, and country of origin are significant determinants of NHL player salaries.

Shadow banking from China's perspective: an empirical analysis of bank-issued wealth management products

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Syed Mehmood Raza Shah ◽  
Qiang Fu ◽  
Ghulam Abbas ◽  
Muhammad Usman Arshad
Keyword(s):  
Commercial Banks ◽  
Fixed Effects ◽  
Banking Sector ◽  
Balance Sheet ◽  
Estimation Method ◽  
Least Square ◽  
Shadow Banking ◽  
Content Type ◽  
Wealth Management ◽  
Chinese Banks

PurposeWealth Management Products (WMPs) are the largest and most crucial component of China's Shadow banking, which are off the balance sheet and considered as a substitute for deposits. Commercial banks in China are involved in the issuance of WMPs mainly to; evade the regulatory restrictions, move non-performing loans away from the balance sheet, chase the profits and take advantage of yield spread (the difference between WMPs yield and deposit rate).Design/methodology/approachIn this study, the authors investigate what bank related characteristics and needs; influenced and prompted the issuance of WMPs. By using a quarterly panel data from 2010 to 2019, this study performed the fixed effects approach favored by the Hausman specification test, and a feasible generalized least square (FGLS) estimation method is employed to deal with any issues of heteroscedasticity and auto-correlation.FindingsThis study found that there is a positive and significant association between the non-performing loan ratio and the issuance of WMPs. Moreover, profitability and spread were found to play an essential role in the issuance of WMPs. The findings of this study suggest that WMPs are issued for multi-purpose, and off the balance sheet status of these products makes them very lucrative for regulated Chinese commercial banks.Research limitations/implicationsNon-guaranteed WMPs are considered as an item of shadow banking in China, as banks do not consolidate this type of WMPs into their balance sheet; due to that reason, there is no individual bank data available for the amount of WMPs. The authors use the number of WMPs issued by banks as a proxy for the bank's exposure to the WMPs business.Practical implicationsFrom a regulatory perspective, this study helps regulators to understand the risk associated with the issuance of WMPs; by providing empirical evidence that Chinese banks issue WMPs to hide the actual risk of non-performing loans, and this practice could mislead the regulators to evaluate the bank credit risk and loan quality. This study also identifies that Chinese banks issue WMPs for multi-purpose; this can help potential investors to understand the dynamics of WMPs issuance.Originality/valueThis research is innovative in its orientation because it is designed to investigate the less explored wealth management products (WMPs) issued by Chinese banks. This study's content includes not only innovation but also contributes to the existing literature on the shadow banking sector in terms of regulatory arbitrage. Moreover, the inclusion of FGLS estimation models, ten years of quarterly data, and the top 30 Chinese banks (covers 70% of the total Chinese commercial banking system's assets) make this research more comprehensive and significant.

scholarly journals The Impact of Inflation Volatility on an Enterprise’s Innovation Strategy

2019 ◽  
Vol 8 (12) ◽  
pp. 193-197
Keyword(s):  
Fixed Effects ◽  
Negative Impact ◽  
Generalized Method Of Moments ◽  
Estimation Method ◽  
Innovation Strategy ◽  
Potential Output ◽  
Economic Agents ◽  
Inflation Volatility ◽  
High Inflation ◽  
The Impact

The objective of the study was to determine the effect of inflation volatility on an enterprise's innovation strategy. The study showed that increasing inflation leads to a decrease in the stationary level of potential output, as well as to a decrease in the rate of economic growth in the process of transition to a stationary state. A formula is proposed for calculating the total effect of inflation on the level of enterprise output. The negative impact of the inflation rate on the welfare of economic agents was revealed, which is expressed in the fall in their equilibrium consumption level. Higher-income countries have been shown to suffer more from high inflation than poorer countries. All conclusions made in the analysis of the dynamic model of the impact of inflation on potential output are verified based on econometric modelling using methods and models for panel data: models with fixed effects, models with random effects, and a generalized method of moments. Moreover, the obtained empirical results are stable concerning changes in the specification of the equation and estimation method

EXPRESS: Handling Endogenous Regressors using Copulas: A Generalization to Linear Panel Models with Fixed Effects and Correlated Regressors

2021 ◽  
pp. 002224372110708
Author(s):  
Rouven E. Haschka
Keyword(s):  
Fixed Effects ◽  
Estimation Method ◽  
Copula Function ◽  
Small Time ◽  
Joint Estimation ◽  
Gaussian Copula ◽  
Correlated Errors ◽  
Finite Sample ◽  
Panel Models ◽  
Endogenous Regressors

This paper proposes a panel data generalization for a recently suggested IVfree estimation method that builds on joint estimation. The author shows how the method can be extended to linear panel models by combining fixed-effects transformations with the common GLS transformation to allow for heterogeneous intercepts. To account for between-regressor dependence, the author proposes determining the joint distribution of the error term and all explanatory variables using a Gaussian copula function, with the distinction that some variables are endogenous and the others are exogenous. The identification does not require any instrumental variables if the regressor-error relation is nonlinear. With a normally distributed error, nonnormally distributed endogenous regressors are therefore required. Monte Carlo simulations assess the finite sample performance of the proposed estimator and demonstrate its superiority to conventional instrumental variable estimation. A specific advantage of the proposed method is that the estimator is unbiased in dynamic panel models with small time dimensions and serially correlated errors; therefore, it is a useful alternative to GMM-style instrumentation. The practical applicability of the proposed method is demonstrated via an empirical example.

scholarly journals A Nonlinear Mixed-Effects Height-to-Diameter Ratio Model for Several Tree Species Based on Czech National Forest Inventory Data

Forests ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 70 ◽  
Author(s):  
Ram Sharma ◽  
Zdeněk Vacek ◽  
Stanislav Vacek ◽  
Miloš Kučera
Keyword(s):  
Forest Inventory ◽  
Stand Density ◽  
Development Stage ◽  
National Forest Inventory ◽  
Mixed Effects ◽  
Site Quality ◽  
National Forest ◽  
Stand Development ◽  
Inventory Data ◽  
Canopy Layer

Height-to-diameter at breast height (DBH) ratio (HDR) is an important tree and stand stability measure. Several factors such as stand dynamics, natural and anthropogenic disturbances, and silvicultural tending significantly affect HDR, and, therefore, in-depth investigation of HDR is essential for better understanding of ecological processes in a forest. A nonlinear mixed-effects HDR model applicable to several tree species was developed using the Czech national forest inventory data comprising 13,875 sample plots and 348,980 trees. The predictive performance of this model was evaluated using the independent dataset which was originated from 25,146 trees on 220 research sample plots. Among various tree- and stand-level variables describing tree size, site quality, stand development stage, stand density, inter-tree spacing, and competition evaluated, dominant height (HDOM), dominant diameter (DDOM), relative spacing index (RS), and DBH-to-quadratic mean DBH ratio (dq) were identified as the most important predictors of HDR variations. A random component describing sample plot-specific HDR variations was included through mixed-effects modelling, and dummy variables describing species-specific HDR variations and canopy layer-specific HDR variations were also included into the HDR model through dummy variable modelling. The mixed-effects HDR model explained 79% of HDR variations without any significant trends in the residuals. Simulation results showed that HDR for each canopy layer increased with increasing site quality and stand development stage (increased HDOM) and increasing competition (increased RS, decreased DDOM and dq). Testing the HDR model on the independent data revealed that more than 85% of HDR variations were described for each individual species (Norway spruce, Scots pine, European larch, and European beech) and group of species (fir species, oak species, birch and alder species) without significant trends in the prediction errors. The HDR can be predicted with a higher accuracy using the calibrated mixed-effects HDR model from measurements of its predictors that can be obtained from routine forest inventories. To improve the prediction accuracy, a model needs to be calibrated with the random effects estimated using one to four randomly selected trees of a particular species or group of species depending on the availability of their numbers per sample plot. The HDR model can be applied for stand stability assessment and stand density regulation. The HDR information is also useful for designing a stand density management diagram. Brief implications of the HDR model for designing silviculture strategies and forest management planning are presented in the article.

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