Linda Lee Ho

Main quality programs characteristics in large size Brazilian companies

Purpose – The purpose of this paper is to identify the relationships as to complementarities and redundancies of the main quality programs in large Brazilian companies by a comparative and critical analysis of their implementation in those companies.Design/methodology/approach – In the paper the survey methodology was utilized. The data collection was done from “Ranking Valor 1000” list, which comprises the 1,000 largest Brazilian companies; the assumption was that in these companies the embryos of the emerging models in quality management were to be found. The data collected from questionnaires were analyzed through statistical methods.Findings – The findings showed that the large organizations in Brazil have been investing in quality programs.Research limitations/implications – This paper presents the limitations which are inherent to the research method applied, that is, the results should not be generalized because the collected data are not originated in a probabilistic sample.Practical implications ...

GENERALIZED LEAST SQUARES METHODS FOR BIVARIATE POISSON REGRESSION

We consider bivariate Poisson regression models to analyse bivariate counts obtained under a stratified sampling scheme. A hybrid maximum likelihood (ML)/generalized least squares (GLS) method is used to obtain estimates of the relevant parameters. The proposed two stage procedure is asymptotically equivalent to and computationally simpler than that based exclusively on maximum likelihood. We compare the results obtained under both methods via a numerical illustration with real data as well as via a simulation study.

Implementação e difusão do programa Seis Sigma no Brasil

The objectives of this paper are to identify the degree of diffusion, the main aspects of the Six Sigma program implementation and its results in the largest Brazilian companies. The research methodology approach was a survey, data were gathered from a structured questionnaire answered by 198 professionals responsible for the quality area in largest Brazilian companies from different sectors. The results pointed out that even in the largest companies; the diffusion of the Six Sigma quality program is not expressive (23.5%). In most of the companies that have implemented such quality program had yet other quality programs implemented. Financial profits and quality and productivity improvement were results reported by the respondents. Moreover, the companies highlight the synergy of the Six Sigma program and other quality management approaches.

Procedimentos inferenciais em índices de capacidade para dados autocorrelacionados via bootstrap

This paper presents procedures to build confidence intervals for capability indices Cp and Cpk based on bootstrap (resampling) methodology when data from the normal process are autocorrelated.

The Six Sigma program: an empirical study of Brazilian companies

Purpose – The purpose of this paper is to assess the status of Six Sigmas status in Brazilian companies and understand the integration of this program with other quality management approaches. Additionally, the critical success factors (CSFs) for Six Sigma implementation and primary Six Sigma program characteristics were identified. Finally, the results of the used of Six Sigma were analysed. Design/methodology/approach – An extensive literature review illustrates the primary Six Sigma characteristics and its relationship with other quality approaches. The research methodology encompasses survey development and statistical analyses. Questionnaires are distributed to 1,000 large firms in the manufacturing and service industries in Brazil. Altogether, a total of 198 firms, of which 46 companies adopted the Six Sigma program, participated in this study. Findings – The results suggest a synergic and incremental pattern of quality model implementation. The study reveals that companies that have adopted Six Si...

Integrating on-line process control and imperfect corrective maintenance: An economical design

Existing studies of on-line process control are concerned with economic aspects, and the parameters of the processes are optimized with respect to the average cost per item produced. However, an equally important dimension is the adoption of an efficient maintenance policy. In most cases, only the frequency of the corrective adjustment is evaluated because it is assumed that the equipment becomes “as good as new” after corrective maintenance. For this condition to be met, a sophisticated and detailed corrective adjustment system needs to be employed. The aim of this paper is to propose an integrated economic model incorporating the following two dimensions: on-line process control and a corrective maintenance program. Both performances are objects of an average cost per item minimization. Adjustments are based on the location of the measurement of a quality characteristic of interest in a three decision zone. Numerical examples are illustrated in the proposal.

Monitoring a wandering mean with an np chart

Este artigo considera um grafico npx proposto por Wu et al. (2009) para controle de media de processo como uma alternativa ao uso do grafico de . O que distingue do grafico de controle npx e o fato das unidades amostrais serem classificadas como unidades de primeiro ou de segunda classe de acordo com seus limites discriminantes. O grafico tradicional np e um caso particular do grafico npx quando os limites discriminantes coincidem com os limites de especificacao e unidade de primeira (segunda) classe e um item conforme (nao conforme). Estendendo o trabalho de Reynolds Junior, Arnold e Baik (1996), consideramos que a media de processo oscila mesmo na ausencia de alguma causa especial. As propriedades de Cadeia de Markov foram adotadas para avaliar o desempenho do grafico npx no monitoramento de media de processos que oscila. De modo geral, o grafico npx requer amostras duas vezes maior para superar desempenho do grafico (enquanto que o grafico tradicional np necessita tamanho de amostras cinco ou seis vezes maior).

Diagnostic errors and repetitive sequential classifications in on-line process control by attributes

The procedure of on-line process control by attributes, known as Taguchis on-line process control, consists of inspecting the mth item (a single item) at every m produced items and deciding, at each inspection, whether the fraction of conforming items was reduced or not. If the inspected item is non-conforming, the production is stopped for adjustment. As the inspection system can be subject to diagnosis errors, one develops a probabilistic model that classifies repeatedly the examined item until a conforming or b non-conforming classification is observed. The first event that occurs (a conforming classifications or b non-conforming classifications) determines the final classification of the examined item. Proprieties of an ergodic Markov chain were used to get the expression of average cost of the system of control, which can be optimized by three parameters: the sampling interval of the inspections (m); the number of repeated conforming classifications (a); and the number of repeated non-conforming classifications (b). The optimum design is compared with two alternative approaches: the first one consists of a simple preventive policy. The production system is adjusted at every n produced items (no inspection is performed). The second classifies the examined item repeatedly r (fixed) times and considers it conforming if most classification results are conforming. Results indicate that the current proposal performs better than the procedure that fixes the number of repeated classifications and classifies the examined item as conforming if most classifications were conforming. On the other hand, the preventive policy can be averagely the most economical alternative rather than those ones that require inspection depending on the degree of errors and costs. A numerical example illustrates the proposed procedure.

Attribute Charts for Monitoring the Mean Vector of Bivariate Processes

This article proposes two Shewhart charts, denoted npxy and npw charts, which use attribute inspection to control the mean vector (μx; μy)′ of bivariate processes. The units of the sample are classified as first-class, second-class, or third-class units, according to discriminate limits and the values of their two quality characteristics, X and Y. When the npxy chart is in use, the monitoring statistic is M = N1 + N2, where N1 and N2 are the number of sample units with a second-class and third-class classification, respectively. When the npw chart is in use, the monitoring statistic is  W = N1 + 2N2. We assume that the quality characteristics X and Y follow a bivariate normal distribution and that the assignable cause shifts the mean vector without changing the covariance matrix. In general, the synthetic npxy and npw charts require twice larger samples to outperform the T2 chart. Copyright

Control charts for individual observations of a bivariate Poisson process

In this paper, three single-control charts are proposed to monitor individual observations of a bivariate Poisson process. The specified false-alarm risk, their control limits, and ARLs were determined to compare their performances for different types and sizes of shifts. In most of the cases, the single charts presented better performance rather than two separate control charts (one for each quality characteristic). A numerical example illustrates the proposed control charts.