Accounting for Uncertainty in Heteroscedasticity in Nonlinear Regression

Toxicologists and pharmacologists often describe toxicity of a chemical using parameters of a nonlinear regression model. Thus estimation of parameters of a nonlinear regression model is an important problem. The estimates of the parameters and their uncertainty estimates depend upon the underlying error variance structure in the model. Typically, a priori the researcher would not know if the error variances are homoscedastic (i.e., constant across dose) or if they are heteroscedastic (i.e., the variance is a function of dose). Motivated by this concern, in this paper we introduce an estimation procedure based on preliminary test which selects an appropriate estimation procedure accounting for the underlying error variance structure. Since outliers and influential observations are common in toxicological data, the proposed methodology uses M-estimators. The asymptotic properties of the preliminary test estimator are investigated; in particular its asymptotic covariance matrix is derived. The performance of the proposed estimator is compared with several standard estimators using simulation studies. The proposed methodology is also illustrated using a data set obtained from the National Toxicology Program.     

A modified LGB method for detecting significant effects based on a half-normal probability plot

In analyzing data from unreplicated factorial designs, the half-normal probability plot is commonly used to screen for the ‘vital few’ effects. Recently, many formal methods have been proposed to overcome the subjectivity of this plot. Lawson (1998) (hereafter denoted as LGB) suggested a hybrid method based on the half-normal probability plot, which is a blend of Lenth (1989) and Loh (1992) method. The method consists of fitting a simple least squares line to the inliers, which are determined by the Lenth method. The effects exceeding the prediction limits based on the fitted line are candidates for the vital few effects. To improve the accuracy of partitioning the effects into inliers and outliers, we propose a modified LGB method (hereafter denoted as the Mod_LGB method), in which more outliers can be classified by using both the Carling’s modification of the box plot (Carling, 2000) and Lenth method. If no outlier exists or there is a wide range in the inliers as determined by the Lenth method, more outliers can be found by the Carling method. A simulation study is conducted in unreplicated $2^4$ designs with the number of active effects ranging from 1 to 6 to compare the efficiency of the Lenth method, original LGB methods, and the proposed modified version of the LGB method.     

Farmers' Contribution to Agricultural Social Capital: Evidence from Southern Spain

Social capital is the whole set of shared norms, values, attitudes, and beliefs that promote cooperation among individuals within the community and that has proved to be a key factor in explaining development processes. This article aims to provide an analytically reliable notion of social capital within the farming sector and a methodological tool for empirically measuring how social capital is accumulated at the farmer level. The theoretical framework proposed is based on the multidimensionality of the complex concept of social capital. Thus, to develop a comprehensive index for social capital, we identify three dimensions of the concept, structural, relational, and cognitive social capital, each one also comprising several subdimensions. This integrative approach permits creation of a composite indicator of the agricultural social capital accumulated at the farmer level, further identifying socioeconomic factors that influence its accumulation at that level. We empirically apply this methodological approach to farmers in Andalusia in southern Spain as a case study. This research provides an interesting starting point for informing policymakers about social capital and helping them implement the necessary programs to facilitate sustainable development in the agricultural sector.     

On second-order improved estimation of a gamma scale parameter

This paper concludes our comprehensive study on point estimation of model parameters of a gamma distribution from a second-order decision theoretic point of view. It should be noted that efficient estimation of gamma model parameters for samples ‘not large’ is a challenging task since the exact sampling distributions of the maximum likelihood estimators and its variants are not known. Estimation of a gamma scale parameter has received less attention from the earlier researchers compared to shape parameter estimation. What we have observed here is that improved estimation of the shape parameter does not necessarily lead to improved scale estimation if a natural moment condition (which is also the maximum likelihood restriction) is satisfied. Therefore, this work deals with the gamma scale parameter estimation as a separate new problem, not as a by-product of the shape parameter estimation, and studies several estimators in terms of second-order risk.     

How the acculturation of Baba Nyonya community affects Malacca food identity?

ABSTRACT

The migration of the Chinese community to Malacca in the 16th century has enabled the process of cross culturing and culinary acculturation, producing a unique mixture of Baba Nyonya food. Even though Baba Nyonya food is pretty much has been localised (Malay), its Chinese representation cannot be denied. This study aims to assess how the acculturation of the Baba Nyonya community affects Malacca food identity. A quantitative methodology is employed in this study. This study classifies Baba Nyonya food acculturation through (1) types of food; (2) methods of cooking; (3) ingredients; and (4) eating decorum. From the regression analysis, this study found that Baba Nyonya cultural polarity explains significant variation in the formation of Malacca food identity. This study then elaborates on the importance of Baba Nyonya food in Malacca destination branding.     

How publics’ active and passive communicative behaviors affect their tornado responses: An integration of STOPS and SMCC

During imminent threat crises, such as natural disasters, publics have minutes to decide how to respond after receiving a warning. This study advances understanding of publics’ crisis communicative and noncommunicative behaviors in the context of tornadoes through combining and extending two theories: the social-mediated crisis communication (SMCC) model and the situational theory of problem solving (STOPS). Findings from a survey of Southeast U.S. residents (n = 1,585) indicate that STOPS is internally consistent and accurate at measuring its intended outcomes of communicative action in problem solving. However, the STOPS measures do not have a significant relationship with the desirable outcome for imminent threat crisis communication: individuals following government’s protective action guidance about tornadoes. In comparison, the expanded SMCC model predicts individuals’ self-reported compliance. Finally, variables from the SMCC model and tornado-specific variables were integrated into the STOPS model to explain individuals’ communicative engagement. Implications for theory and public relations practice are discussed.     

Fabric that weaves stories: Pua kumbu and contemporary Iban identity construction in Sarawak,Malaysia

This article examines the process of identity construction among the Iban indigenous people of Sarawak in Malaysia through pua kumbu – their sacred and ritual cloth. Although the Ibans are popularly known for their headhunting practices and longhouse dwellings, these cultural practices are in major decline and therefore pua kumbu is brought to the forefront as a significant means of identity construction. By illustrating the meanings, narratives, and ceremonies associated with pua kumbu, this article demonstrates that pua kumbu is not just a piece of sacred or ritual cloth; rather, it has significant meanings in the everyday life of the Ibans. It connects the Ibans with distinctly eternal meanings of their life and cosmology, past histories, and their connections to the physical environment. It thus helps the process of maintaining a boundary and identity construction of the Ibans by distinguishing between ‘us and them’ – the Ibans and others.     

International Remittances and Private Schooling: Evidence from Kerala,India

This study investigates the impact of international remittances on private school enrolment in Kerala. Using data from the 2010 Kerala Migration Survey and employing an instrumental variable (IV‐Probit) approach to address the endogeneity of migration, we found that remittances have a positive and significant effect on private school enrolment. After disaggregating the sample into different heterogeneous groups, we found that remittances have greater effect on boys, children residing in rural areas, and those belonging to socially advantageous groups and from higher wealth quintile. Children from lower wealth quintile and belonging to socially disadvantageous groups are least affected by migration and remittances.