On the estimation of serial correlation in Markov-dependent production processes

In this paper, we present a study about the estimation of the serial correlation for Markov chain models which is used often in the quality control of autocorrelated processes. Two estimators, non-parametric and multinomial, for the correlation coefficient are discussed. They are compared with the maximum likelihood estimator [U.N. Bhat and R. Lal, Attribute control charts for Markov dependent production process, IIE Trans. 22 (2) (1990), pp. 181–188.] by using some theoretical facts and the Monte Carlo simulation under several scenarios that consider large and small correlations as well a range of fractions (p) of non-conforming items. The theoretical results show that for any value of p≠0.5 and processes with autocorrelation higher than 0.5, the multinomial is more precise than maximum likelihood. However, the maximum likelihood is better when the autocorrelation is smaller than 0.5. The estimators are similar for p=0.5. Considering the average of all simulated scenarios, the multinomial estimator presented lower mean error values and higher precision, being, therefore, an alternative to estimate the serial correlation. The performance of the non-parametric estimator was reasonable only for correlation higher than 0.5, with some improvement for p=0.5.     

Revised GRASP with path-relinking for the linear ordering problem

The linear ordering problem (LOP) is an NP\mathcal{NP}-hard combinatorial optimization problem with a wide range of applications in economics, archaeology, the social sciences, scheduling, and biology. It has, however, drawn little attention compared to other closely related problems such as the quadratic assignment problem and the traveling salesman problem. Due to its computational complexity, it is essential in practice to develop solution approaches to rapidly search for solution of high-quality. In this paper we propose a new algorithm based on a greedy randomized adaptive search procedure (GRASP) to efficiently solve the LOP. The algorithm is integrated with a Path-Relinking (PR) procedure and a new local search scheme. We tested our implementation on the set of 49 real-world instances of input-output tables (LOLIB instances) proposed in Reinelt (Linear ordering library (LOLIB) 2002). In addition, we tested a set of 30 large randomly-generated instances proposed in Mitchell (Computational experience with an interior point cutting plane algorithm, Tech. rep., Mathematical Sciences, Rensellaer Polytechnic Institute, Troy, NY 12180-3590, USA 1997). Most of the LOLIB instances were solved to optimality within 0.87 seconds on average. The average gap for the randomly-generated instances was 0.0173% with an average running time of 21.98 seconds. The results indicate the efficiency and high-quality of the proposed heuristic procedure.     

Rural population and social security in Brazil: An analysis with emphasis on constitutional changes

This paper analyses the situation of the Brazilian rural population with respect to social insurance and social assistance at two points in time: 1988 and 1998. The 1988 Constitution defined new rules with regard to eligibility conditions and benefit values for the rural population. But it was only in July 1991, with Law 8213, that these changes were implemented. We compare — by gender and individual age — activity rates and probability of receiving benefits, before and after the changes in legislation. We also compare, at these two points in time, family structure and the importance of the income of older people in the family budget. The analysis makes clear the positive impact brought by the legislation on the coverage and per capita family income of those families with older members in rural Brazil, bringing about some degree of poverty alleviation, as well as bridging the gender gap with respect to access to benefits. In contrast to what occurs in other Latin American countries, nowadays the Brazilian rural population has almost universal access to social security benefits, not only at family level but also in individual terms.     

A note on the correlation structure of transformed Gaussian random fields

Transformed Gaussian random fields can be used to model continuous time series and spatial data when the Gaussian assumption is not appropriate. The main features of these random fields are specified in a transformed scale, while for modelling and parameter interpretation it is useful to establish connections between these features and those of the random field in the original scale. This paper provides evidence that for many ‘normalizing’ transformations the correlation function of a transformed Gaussian random field is not very dependent on the transformation that is used. Hence many commonly used transformations of correlated data have little effect on the original correlation structure. The property is shown to hold for some kinds of transformed Gaussian random fields, and a statistical explanation based on the concept of parameter orthogonality is provided. The property is also illustrated using two spatial datasets and several ‘normalizing’ transformations. Some consequences of this property for modelling and inference are also discussed.     

Alike but not alike: Welfare state and unemployment policies in Southern Europe. Italy and Portugal compared

Although Italy and Portugal are considered to be part of the same welfare state family – the Southern European one – analysis of a key component of the welfare state, namely, unemployment policies and regulations, reveals a different evaluation. A comparative analysis of a series of specific indicators of Italian and Portuguese unemployment regimes shows that they represent two different models. Portugal appears to be a more inclusive system, closer to continental or Northern European countries than it is to Italy, or at least representing a hybrid system that combines characteristics of continental European welfare states with characteristics that are more typical of Southern European welfare states. Italy, on the contrary, is much more clearly a Southern European welfare state.     

Asymptotic linearity and limit distributions,approximations

Linear and quadratic forms as well as other low degree polynomials play an important role in statistical inference. Asymptotic results and limit distributions are obtained for a class of statistics depending on μ+X$\mu +\mathbf{X}$, with X any random vector and μ$\mu$ non-random vector with ∥μ∥→+∞$\parallel \mu \parallel \to +\infty$. This class contain the polynomials in μ+X$\mu +\mathbf{X}$. An application to the case of normal X is presented. This application includes a new central limit theorem which is connected with the increase of non-centrality for samples of fixed size. Moreover upper bounds for the suprema of the differences between exact and approximate distributions and their quantiles are obtained.     

Empowering,invasive or a little bit of both? A reflection on the use of visual and narrative methods in research with migrant sex workers in South Africa

Although migration plays a critical role in the economic landscape of the world, government officials and researchers do not sufficiently include migration and/or migrants in research studies and development policies. In South Africa, many migrants – both internal and cross-border – engage in informal livelihood strategies, including sex work (see Richter et al. 2012). Currently, the bulk of research that is being conducted in South Africa in the areas of migration and sex work rely heavily on the use of traditional research approaches and focus mainly on concerns surrounding issues of public health, with increased attention to HIV (for example, see SANAC 2013; Scheibe, Drame and Shannon 2012; Scorgie et al. 2011). While this work is invaluable, there is a need for research that can counter the stigma that sex workers overwhelmingly face in light of HIV/AIDS. Participatory visual and narrative research approaches – as part of mixed method study designs – that examine the lived experiences of migrant sex workers can provide important insights that ‘move beyond the polarized and simplistic arguments that have circulated in South African about migrant sex workers’ (Nyangairi and Palmary, 2014, 132). This methodological approach makes important and necessary contributions to national and international discourses on migration and sex work (see Oliveira and Vearey 2015). In addition, these methods provide a unique platform where the normative discourses that portray migrants as a homogenous vulnerable and apolitical group of people can be contested (Palmary 2006). In this article, I present and discuss three participatory visual and narrative research projects that have been conducted with migrant men, women and transgender persons who sell sex in two Provinces of South Africa and examine the suitability of these approaches.     

On the Correlation Structure of Gaussian Copula Models for Geostatistical Count Data

We describe a class of random field models for geostatistical count data based on Gaussian copulas. Unlike hierarchical Poisson models often used to describe this type of data, Gaussian copula models allow a more direct modelling of the marginal distributions and association structure of the count data. We study in detail the correlation structure of these random fields when the family of marginal distributions is either negative binomial or zero‐inflated Poisson; these represent two types of overdispersion often encountered in geostatistical count data. We also contrast the correlation structure of one of these Gaussian copula models with that of a hierarchical Poisson model having the same family of marginal distributions, and show that the former is more flexible than the latter in terms of range of feasible correlation, sensitivity to the mean function and modelling of isotropy. An exploratory analysis of a dataset of Japanese beetle larvae counts illustrate some of the findings. All of these investigations show that Gaussian copula models are useful alternatives to hierarchical Poisson models, specially for geostatistical count data that display substantial correlation and small overdispersion.     

Selection of Logistic Service Providers for the transportation of refrigerated goods

The aim of this article is to propose a decision model based on Analytic Hierarchy Process (AHP) for the evaluation and selection of Logistics Service Providers (LSPs) for a refrigerated products company. The results indicated that quality, responsiveness and reliability are the most important criteria for selecting an LSP for the transportation of perishable refrigerated goods, considering contractor’s profile, which is based on protection of its brand and reputation in the market. In addition, sensitivity analysis is performed to verify priority ranking stability. Therefore, this research illustrates how AHP model could be implemented to help the decision-making process for selecting third-party services in logistics for perishable refrigerated goods effectively.