Model Selection Using Conditional Densities

In this article we propose a new method to select a discrete model f(x; θ), based on the conditional density of a sample given the value of a sufficient statistic for θ. The main idea is to work with a broad family of discrete distributions, called the family of power series distribution, for which there is a common sufficient statistic for the parameter of interest. The proposed method uses the maximum conditional density in order to select the best model.

We compare our proposal with the usual methodology based on Bayes factors. We provide several examples that show that our proposal works fine in most instances. Bayes factors are strongly dependent on the prior information about the parameters. Since our method does not require the specification of a prior distribution, it provides a useful alternative to Bayes factors.     

Shortening the distance between Edgeworth and Berry–Esseen in the classical case

We obtain near optimal Berry–Esseen bounds for standardized sums of independent identically distributed random variables. This is achieved by distinguishing the lattice and the non-lattice cases, as one-term Edgeworth expansions do. The main tool is an easy inequality involving the usual second modulus of continuity, in substitution of Esseen's smoothing inequality. An illustrative example concerning the exponential distribution is also considered.     

Appendix. Incomes Policies in Europe during the Eighties

Abstract. Moving off from the lessons of the Italian incomes policy experience of the 1980s, this paper presents a new framework to interpret the performance of incomes policy (LP) agreements and institutions, and propose new strategies for the 1990s. IP is viewed as a cooperative outcome that evolves from a non-cooperative long-term game between several players (workers, unions, firms, government, parliament, etc.), along the lines of the model drawn up by Brunetta and Carraro (1988). The paper is divided into three sections. The first summarizes the history of IP in Italy, starting from the phase of the predetermination of disinflation (1983-84). We firstly outline some of the fundamental features of recent Italian development (the “Italian model”), noting how new IP measures could be taken to create an adequate response to the new European and international deadlines. The difficulties and uncertainties that presently exist at both national and international level make the introduction of IP in new, cooperative and evolutive terms, necessary. The second section examines the various topics and new objectives of a “strategic” IP resumption, particularly relevant to the concerted action on the cost of labour, presently being discussed. The topics we consider are: the link between wage reform and IP; the recent concerted agreements reached on fiscal drag (26.1.89) and on the cost of labour (25.1 and 6.7.90); the importance of the role of productivity gain-sharing; programmed inflation and price control; indexation of gross wages and safeguarding the net wage; increase of the tax base; profit-sharing. The third and final section presents a few observations which further investigate the distribution of productivity gains between sectors and uses: how it is articulated amongst the various bargaining levels (central, sectoral or enterprise). Redistribution amongst sectors is dealt with in terms of “protected” and “unprotected” areas of the economy, showing the need of a concerted regulation at the central level. Sharing between factors and allocations presents a very different case, and is dealt with at sectoral and firm level.     

Mobility and accessibility in historic cities

The historic cities of Brazil, despite its colonial structure, don't fail to go through transformations that affect contemporary cities, which is the main source of problems, leading to new approaches to urban issues such as mobility and accessibility. The uncontrolled growth of tourism in the historic cities can be considered as a big problem, because at the same time, they have committed to the conservation of its built heritage and demand control of the activities that occur in their areas without harm. Then, a permanent dialogue between conservatives and planners could be accomplished by joining the various sectoral policies. The study of urban mobility in historical sites was in fact the focus of this work because of their peculiarities, such as its specific characteristics of urban structure, morphology and occupation. In fact, the development of tourism in historic centers generates specific demands, such as adaptation to new uses of the houses, intensive movement of people and vehicles, illegal parking, among others. Beyond threatening the city preservation, does not provide mobility and accessibility to tourists, because these cities were not designed for the tourism conditions and needs of contemporary life. Characteristic features of Brazilian baroque cities, such as topography , the narrow streets, narrow or nonexistent sidewalks, steep turns and ramps strong, are not suitable for heavy vehicles, traffic and pedestrian circulation. Thus, studies concerning conservation urban integrated are aimed at an approach to interaction between historic preservation of the environment with the dynamic socio-economic of the local.     

PLUG-IN ESTIMATION OF GENERAL LEVEL SETS

Given an unknown function (e.g. a probability density, a regression function, …) f and a constant c, the problem of estimating the level set L(c) ={f≥c} is considered. This problem is tackled in a very general framework, which allows f to be defined on a metric space different from . Such a degree of generality is motivated by practical considerations and, in fact, an example with astronomical data is analyzed where the domain of f is the unit sphere. A plug‐in approach is followed; that is, L(c) is estimated by L_n(c) ={f_n≥c} , where f_n is an estimator of f. Two results are obtained concerning consistency and convergence rates, with respect to the Hausdorff metric, of the boundaries ?L_n(c) towards ?L(c) . Also, the consistency of L_n(c) to L(c) is shown, under mild conditions, with respect to the L₁ distance. Special attention is paid to the particular case of spherical data.     

‘It's been hell.’ Italian and British practice educators’ narratives of working with struggling or failing social work students in practice learning settings

Periods of assessed learning in practice settings are common requirements for social work students worldwide. The ‘practice learning opportunity’ as it is known in the UK, and ‘tirocinio di servizio sociale’ as it is referred to in Italy, are important sites of gatekeeping in preventing unsuitable people from becoming social workers. The experience of assessing failing students in practice learning settings, however, has been found to be particularly stressful and challenging for practice educators. This article documents findings from two qualitative studies that explored field educators’ experiences of working with struggling or failing social work students in Italy and England. The study finds both similarities and differences in the narratives of the assessors from the two countries. Similarities include, unpleasant emotional experience of working with a failing student, internalisation of the students’ failing as the practice educators’ own failing, perceptions that the universities may hide negative information about students and lack of acknowledgement of the gatekeeping function inherent in the practice educator role. Differences include the level of emotionality experienced by educators, the way students are spoken about and the perceived role and responses of the university. Further comparative European research that focuses on practice education is indicated.     

Truncated location-scale non linear regression models

We present a class of truncated non linear regression models for location and scale where the truncated nature of the data is incorporated into the statistical model by assuming that the response variable follows a truncated distribution. The location parameter of the response variable is assumed to be modeled by a continuous non linear function of covariates and unknown parameters. In addition, the proposed model also allows for the scale parameter of the responses to be characterized by a continuous function of the covariates and unknown parameters. Three particular cases of the proposed models are presented by considering the response variable to follow a truncated normal, truncated skew normal, and truncated beta distribution. These truncated non linear regression models are constructed assuming fixed known truncation limits and model parameters are estimated by direct maximization of the log-likelihood using a non linear optimization algorithm. Standardized residuals and diagnostic metrics based on the cases deletion are considered to verify the adequacy of the model and to detect outliers and influential observations. Results based on simulated data are presented to assess the frequentist properties of estimates, and a real data set on soil-water retention from the Buriti Vermelho River Basin database is analyzed using the proposed methodology.     

Intergenerational mobility of housework time in the United Kingdom

This paper analyzes the relationship between parents’ time devoted to housework and the time devoted to housework by their children. Using data from the Multinational Time Use Study for the UK, we find positive intergenerational correlations in housework for both parents, indicating that the more time parents devote to housework, the more time their children will devote to housework. Using data from the British Household Panel Survey, we find that a higher father–mother housework ratio is positively related to a higher child–mother housework ratio, even after allowing for individual fixed-effects. In order to address the potential exacerbation of errors-in-variables arising from the fixed-effects specification, we instrument the father–mother ratio of housework using father’s and mother’s lagged weekly working hours. The Instrumental-Variable estimates fully support the fixed-effects estimates, and suggest that the latter should be regarded as a lower bound. We also present evidence of the link between housework during adolescence and during adulthood, which may indicate that housework time during adulthood depends on the housework time during childhood, which may also be affected by parents’ housework time. Our results contribute to the field of the intergenerational mobility of behaviors.     

Just-in-time purchasing: an empirical study of operational practices, supplier development and performance

This paper examines the role of supplier development in establishing and managing efficient buyer–supplier operational links. The paper develops and assesses a measurement instrument for “operational” and “supplier development” just-in-time purchasing practices, followed by an examination of the relationships between the two sets, and an investigation into whether the use of “operational” and “supplier development” practices has a bearing on higher plant performance. A plant-level survey was carried out on a sample of electronics and machinery plants. The study empirically:

• documents the close connection between the buyer–supplier operational link and the buyer’s practices for supplier development;

• demonstrates that recourse to supplier development programs and their nature depend on the kind of vendor–vendee operational connection;

• test whether different plant performance outcomes result from the implementing of different “operational” and “supplier development” practices. It demonstrates that better-performing plants exhibit more advanced design and logistic links with sources, more formalised vendor-rating and ranking procedures, greater use of organisational devices for supplier-organisational integration and place greater importance on supplier assistance and training.

Deprivation index for small areas in Spain

The term deprivation is often used to refer to economic or social shortages in a given geographical area. This concept of deprivation has been identified for years using simple indicators such as income level, education and social class. One of the advantages of using simple indicators is the availability of data, since they come directly from sources of information like censuses and population registers. However, the main disadvantage of these indicators is their limited usefulness when measuring a concept as complex as deprivation with a single variable. One possible solution to this problem is using compound indices, made up of a combination of simple indicators. For years, the concept of material deprivation in Spain has been measured using indices or indicators imported from other countries. However, there are no studies that investigate if all of these variables are really related to material deprivation in Spain. In this context, the objective of this study is to create a synthetic index for material deprivation for the municipalities in Spain, bearing in mind the variables available from the Population and Housing Census. The index was built on a principal components factor analysis. The analysis showed two factors. The first factor showed a high positive correlation to the variables relating to illiteracy rate, unemployment rate and percentage of manual labourers, while the second factor was seen as highly positively correlated to the variables relating to the percentage of homes without access to a vehicle and the dependency index and also correlated, though negatively, to the percentage of foreigners between 16 and 49 who lived abroad in 1991. The variables that make up the first factor can be considered to be an approximation of the concept of deprivation in Spain. This study proposes a deprivation index made up of three simple indicators available from national information sources: percentage of illiteracy, percentage of unemployment and percentage of manual labourers. With this index, the criteria for measuring deprivation in Spanish municipalities can be unified and a comparison of the results of the different studies in our context facilitated.