The EWMA sign chart revisited: performance and alternatives without and with ties

The EWMA Sign control chart is an efficient tool for monitoring shifts in a process regardless the observations'' underlying distribution. Recent studies have shown that, for nonparametric control charts, due to the discrete nature of the statistics being used (such as the Sign statistic), it is impossible to accurately compute their Run Length properties using Markov chain or integral equation methods. In this work, a modified nonparametric Phase II EWMA chart based on the Sign statistic is proposed and its exact Run Length properties are discussed. A continuous transformation of the Sign statistic, combined with the classical Markov Chain method, is used for the determination of the chart''s in- and out-of-control Run Length properties. Additionally, we show that when ties occur due to measurement rounding-off errors, the EWMA Sign control chart is no longer distribution-free and a Bernoulli trial approach is discussed to handle the occurrence of ties and makes the proposed chart almost distribution-free. Finally, an illustrative example is provided to show the practical implementation of our proposed chart.     

Coalitional desirability and the equal division value

Theory and Decision - We introduce three natural collective variants of the well-known axiom of desirability (Maschler and Peleg in Pac J Math 18:289–328, 1966), which require that if the...     

Control chart for monitoring the Weibull shape parameter under two competing risks

ABSTRACT

In this paper, we propose a control chart to monitor the Weibull shape parameter where the observations are censored due to competing risks. We assume that the failure occurs due to two competing risks that are independent and follow Weibull distribution with different shape and scale parameters. The control charts are proposed to monitor one or both of the shape parameters of competing risk distributions and established based on the conditional expected values. The proposed control chart for both shape parameters is used in certain situations and allows to monitor both shape parameters in only one chart. The control limits depend on the sample size, number of failures due to each risk and the desired stable average run length (ARL). We also consider the estimation problem of the target parameters when the Phase I sample is incomplete. We assumed that some of the products that fail during the life testing have a cause of failure that is only known to belong to a certain subset of all possible failures. This case is known as masking. In the presence of masking, the expectation-maximization (EM) algorithm is proposed to estimate the parameters. For both cases, with and without masking, the behaviour of ARLs of charts is studied through the numerical methods. The influence of masking on the performance of proposed charts is also studied through a simulation study. An example illustrates the applicability of the proposed charts.     

A Study on EWMA charts with runs rules—the Markov chain approach

ABSTRACT

Runs rules are usually used with Shewhart-type charts to enhance the charts' sensitivities toward small and moderate shifts. Abbas et al. in 2011 took it a step further by proposing two runs rules schemes, applied to the exponentially weighted moving average (EWMA) chart and evaluated their average run length (ARL) performances using simulation. They showed that the proposed schemes are superior to the classical EWMA chart and other schemes being investigated. Besides pointing out some erroneous ARL and standard deviation of the run length (SDRL) computations in Abbas et al., this paper presents a Markov chain approach for computing the ARL, percentiles of the run length (RL) distribution and SDRL, for the two runs rules schemes of Abbas et al. Using Markov chain, we also propose two combined runs rules EWMA schemes to quicken the two schemes of Abbas et al. in responding to large shifts. The runs rules (basic and combined rules) EWMA schemes will be compared with some existing control charting methods, where the former charts are shown to prevail.     

Child Mortality in Beirut: Six Indirect Estimates Based on Data Collected at the Time of a Birth

Six indirect techniques for estimating child mortality were applied to information on survival status of all children ever born, provided by a sample of 1,252 women delivered at the Maternity Unit of the American University of Beirut Hospital. The results were compared, using as a reference the estimate derived from partial birth histories (ages of surviving children, ages at death of children who have died). Their dispersion is minimal for the probability of dying between birth and fifth birthday, estimated at 48 per thousand. For each mother, the ratio of the observed number of children who have died, to that expected given the lengths of exposure of the children to the risk of mortality, was used as a dependent variable in a multiple regression analysis. Educational level of mothers had a significant effect, but not occupational status of father, religion or consanguinuity.     

DO FINANCIAL INCENTIVES AFFECT FIRMS’ DEMAND FOR DISABLED WORKERS?

A number of OECD countries aim to encourage work integration of disabled persons using quota policies. For instance, Austrian firms must provide at least one job to a disabled worker per 25 nondisabled workers and are subject to a tax if they do not. This “threshold design” provides causal estimates of the noncompliance tax on disabled employment if firms do not manipulate nondisabled employment; a lower and upper bound on the causal effect can be constructed if they do. Results indicate that firms with 25 nondisabled workers employ about 0.04 (or 12%) more disabled workers than without the tax; firms do manipulate employment of nondisabled workers but the lower bound on the employment effect of the quota remains positive; employment effects are stronger in low‐wage firms than in high‐wage firms; and firms subject to the quota of two disabled workers or more hire 0.08 more disabled workers per additional quota job. Moreover, increasing the noncompliance tax increases excess disabled employment, whereas paying a bonus to overcomplying firms slightly dampens the employment effects of the tax.     

Interaction Patterns in Adolescent Romantic Relationships: A Typological Analysis

While several studies in adolescents have addressed issues related to romantic relationships and dating violence, there is a limited understanding of their interaction patterns. This study aims to document interactions in conflict situations by identifying profiles of adolescent romantic relationships. Qualitative analysis based on the dimensions of the Circumplex Model of Marital and Family Systems was used to investigate the interaction task of 40 dyads. A typological analysis revealed four profiles: (1) rigid, (2) entangled, (3) hampered, and (4) balanced. Results highlight the diversity of romantic experiences and offer a better understanding of the intricacies of different interaction profiles. Dating violence prevention efforts and programs promoting harmonious and egalitarian romantic relationships could benefit from the insights of the identified profiles.     

Identifying Social Indicators for Sustainability Assessment of CCU Technologies: A Modified Multi-criteria Decision Making

Social Indicators Research - This paper analyses the trend and changes in Sri Lanka’s multidimensional poverty before the ethnic war in 2007, the transition through 2009 and after the war in...     

More Than a Piece of Paper? Protection Orders as a Resource for Battered Women

Nearly 2 million women are assaulted by a partner or ex‐partner each year in the United States ( Tjaden and Thoennes 2000 ). Intimate partner violence is a complex social problem rooted in structural gender inequality, but that affects individual women in different ways (e.g. Crenshaw, 1991 ; Stark 2008 ). Battered women actively seek help in ending the violence from both formal and informal sources (e.g. Campbell et al. 1998 ; Stark 2008 ; Sullivan and Bybee 1999 ). As part of this process, many battered women will apply for a protection order against their batterer; nearly 1 million such orders are issued every year ( Tjaden and Thoennes 2000 ). This article reviews the research on the effectiveness of such orders, including access and enforcement, and provides suggestions for further research and policy improvements.