Comparison of Operating Characteristics of Commonly Used Sample Size Re-Estimation Procedures in a Two-Stage Design

In group sequential clinical trials, there are several sample size re-estimation methods proposed in the literature that allow for change of sample size at the interim analysis. Most of these methods are based on either the conditional error function or the interim effect size. Our simulation studies compared the operating characteristics of three commonly used sample size re-estimation methods, Chen et al. (2004), Cui et al. (1999), and Muller and Schafer (2001). Gao et al. (2008) extended the CDL method and provided an analytical expression of lower and upper threshold of conditional power where the type I error is preserved. Recently, Mehta and Pocock (2010) extensively discussed that the real benefit of the adaptive approach is to invest the sample size resources in stages and increasing the sample size only if the interim results are in the so called “promising zone” which they define in their article. We incorporated this concept in our simulations while comparing the three methods. To test the robustness of these methods, we explored the impact of incorrect variance assumption on the operating characteristics. We found that the operating characteristics of the three methods are very comparable. In addition, the concept of promising zone, as suggested by MP, gives the desired power and smaller average sample size, and thus increases the efficiency of the trial design.     

All in the Family: How Do Social Capital and Material Wellbeing Affect Relational Wellbeing?

We use a unique dataset from Italy to investigate the impact of socioeconomic characteristics and social capital on family wellbeing and satisfaction. We assess wellbeing using four dimensions of satisfaction with family life: satisfaction with decision making processes, with relationships with partner and children, and with time spent with children. Social capital is measured through information about membership in organizations, trust, and interactions with others. We find that while socioeconomic characteristics in general do not have strong effects on family wellbeing, social capital matters for family life satisfaction.

     

Designing of variables quick switching sampling system by considering process loss functions

This paper proposes a variables quick switching system where the quality characteristic of interest follows a normal distribution and the quality characteristic is evaluated through a process loss function. Most of the variables sampling plans available in the literature focus only on the fraction non-conforming and those plans do not distinguish between the products that fall within the specification limits. The products that fall within specification limits may not be good if their mean is too away from the target value. So developing a sampling plan by considering process loss is inevitable in these situations. Based on this idea, we develop a variables quick switching system based on the process loss function for the application of the processes requiring low process loss. Tables are also constructed for the selection of parameters of variables quick switching system for given acceptable quality level and limiting quality level. The results are explained with examples.     

Perceived Discrimination and Its Associations With Mental Health and Substance Use Among Asian American and Pacific Islander Undergraduate and Graduate Students

Abstract

Objectives: Racial discrimination experiences can negatively affect health. This study examined perceived discrimination and its relationship with mental health and substance use among Asian American and Pacific Islander (API) undergraduate and graduate students. Participants: A total of 113 API students aged 18–35 completed the study during February–June, 2011. Methods: The authors conducted a cross-sectional, anonymous survey online. Dependent variables included mental health (depressive, anxiety, and somatic symptoms) and substance use (alcohol problems, use of tobacco, marijuana or hashish, and other illegal drugs). Results: Students’ perceived discrimination were significantly, positively associated with depressive, anxiety, and somatic symptoms, but not with substance use. Ethnic identity moderated the relationship between perceived discrimination and somatic symptoms, but not depressive or anxiety symptoms. Conclusions: These findings suggested the negative effect of racial discrimination on API students’ mental health. The buffering effect of ethnic identity may increase resilience in these students when they face racial discrimination.     

Micro Ruptures and Repairs in the Beginning Phase of Cross-Cultural Psychotherapy

The article discusses misunderstandings and misattunements that occur in the beginning phase of cross-cultural psychotherapy. Sources of micro ruptures are outlined, including client maladaptive patterns, therapist misunderstandings, cross-cultural misunderstandings due to cultural variations, and asymmetrical power relations involving the impact of prior experiences or current therapy practices. Multiple clinical vignettes illustrate the rupture/repair process, drawing on Safran and Muran’s (2000) list of direct and indirect techniques.     

Union rent seeking and import competition

conclusion We empirically evaluate two issues: (1) how the union rent seeking responds to import competition and (2) whether union bargaining power, as proxied by the proportion of the labor force in an industry that is unionized, moderates the impact of import com-petition on union wage differentials. Unlike other studies, our emphasis is on the influ-ence of import competition on union rent seeking, rather than on union wages per se. Our primary results indicate that while import competition negatively and significantly affects union rent seeking, the extent of unionization does not substantially influence the impact of import competition on the union wage differentials. This is a somewhat surprising result since the literature suggests that union wages are greater in the pres-ence of stronger unions.     

Developing and designing of an efficient variables sampling system based on the process capability index

Process capability indices (PCIs) are extensively used in the manufacturing industries in order to confirm whether the manufactured products meet their specifications or not. PCIs can be used to judge the process precision, process accuracy, and the process performance. So developing of sampling plans based on PCIs is inevitable and those plans will be very much useful for maintaining and improving the product quality in the manufacturing industries. In view of this, we propose a variables sampling system based on the process capability index C_pmk, which takes into account of process yield and process loss, when the quality characteristic under study will have double specification limits. The proposed sampling system will be effective in compliance testing. The advantages of this system over the existing sampling plans are also discussed. In order to determine the optimal parameters, tables are also constructed by formulating the problem as a nonlinear programming in which the average sample number is minimized by satisfying the producer and consumer risks.     

Developing of a new system of skip-lot reinspection schemes

The skip-lot sampling plans are widely used in industries for quality inspection of products in order to reduce the sampling costs and inspection efforts when products have good quality history. Also, the skip-lot sampling plan concept is sound and useful and it is economically advantageous to use the skip-lot approach in the design of sampling plans. Thus, the skip-lot sampling plans are useful to minimize the cost of the inspection particularly in costly and destructive testing. Hence, a new system of skip-lot sampling plans designated as SkSP-2-R plan is developed in this article by incorporating the idea of resampling procedure in the skip-lot sampling plans of type SkSP-2. A Markov chain formulation and derivation of performance measures for this new plan are presented. The properties and advantages of the SkSP-2-R plan are studied with single sampling plan as the reference plan. The response-to-change characteristics of the SkSP-2-R plan are also investigated, based on the average run length.