Amplitude modulated model for analyzing non-stationary speech signals

Recently amplitude modulated (AM) model in presence of additive white noise was used to analyze certain non-stationary speech data. It is observed that the assumption of white noise may not be proper in many cases. In this article, we consider the AM signal model in presence of stationary noise. We consider the least squares estimators and the estimators obtained by maximizing the Periodogram function. The two estimators are asymptotically equivalent. We study the theoretical properties of both estimators and observe their performances through numerical simulations. One speech data is analyzed and it is observed that the performance of the proposed estimators is quite satisfactory.     

Analysis of middle-censored data with exponential lifetime distributions

Recently Jammalamadaka and Mangalam [2003. Non-parametric estimation for middle censored data. J. Nonparametric Statist. 15, 253–265] introduced a general censoring scheme called the “middle-censoring” scheme in non-parametric set up. In this paper we consider this middle-censoring scheme when the lifetime distribution of the items is exponentially distributed and the censoring mechanism is independent and non-informative. In this set up, we derive the maximum likelihood estimator and study its consistency and asymptotic normality properties. We also derive the Bayes estimate of the exponential parameter under a gamma prior. Since a theoretical construction of the credible interval becomes quite difficult, we propose and implement Gibbs sampling technique to construct the credible intervals. Monte Carlo simulations are performed to evaluate the small sample behavior of the techniques proposed. A real data set is analyzed to illustrate the practical application of the proposed methods.     

The Effect of Product Variety and Inventory Levels on Retail Store Sales: A Longitudinal Study

We examine the effects of product variety and inventory levels on store sales. Using 4 years of data from stores of a large retailer, we show that increases in product variety and inventory levels are both associated with higher sales. We also show that increasing product variety and inventory levels has an indirect negative effect on store sales through their impact on phantom products—products that are physically present at the store, but only in storage areas where customers cannot find or purchase them. Our study highlights a consequence of increased product variety and inventory levels that has previously been overlooked in studies of retail product variety and inventory management. It also quantifies the impact of phantom products on store sales. In addition, our study provides empirical evidence to support earlier claims that higher product variety and inventory levels lead to an increase in defect rate. We discuss the implications of our findings for retail inventory and assortment planning and for the design of retail stores.     

Why Do Men and Women Challenge Gender Discrimination in the Workplace? The Role of Group Status and In-group Identification in Predicting Pathways to Collective Action

Group status and group identification were hypothesized to moderate the predictors of collective action to challenge gender discrimination against women. Higher identifiers were expected to respond to the inequality through the lens of their in-group's interests. Among highly identified women, collective action was predicted by appraisals of illegitimacy and feelings of anger, suggesting that they felt a sense of solidarity with the victims and experienced the justice violation as personally relevant. In contrast, higher identification with the high-status group should reflect more investment in the advantaged in-group, relative to the interests of the victimized out-group members. Thus, among highly identified men, collective action intentions were predicted by perceiving the inequality as pervasive (i.e., not limited to a few cases) and feelings of sympathy for victims. This suggests that highly identified men did not experience the inequality as self-relevant until they saw it as too widespread to be ignored. In contrast, men and women with lower gender group identification demonstrated more similar pathways to collective action, where sympathy was the main predictor. Theoretical and practical implications are discussed.     

Effect of Quality Management Systems and Total Quality Management on Productivity Before and After: Empirical Evidence from the Indian Auto Component Industry

We study the linkages between firm‐level quality initiatives such as quality management systems (QMS) and total quality management (TQM) and output productivity in the Indian auto component industry. We use externally validated quality certification and quality awards as proxies for QMS and TQM, respectively, as it is difficult to directly measure the QMS and TQM efforts of firms. We use an unbalanced panel of 220 firms and a balanced panel of 73 firms from the Indian auto component industry over the period 1993–2006 to study these links. Both parametric as well as non‐parametric approaches are used, as appropriate, to measure the rate of change in productivity and the impact of quality initiatives on productivity change during this period. We determine the proportion of productivity resulting from technical change and relative efficiency change, thus providing insights into the structure of productivity improvements. We find that TQM efforts resulted in a high rate of productivity change (11%) in the award‐winning firms after the award. On the other hand, pre‐certification productivity change due to QMS was 5% and post‐certification change was 3.6%. In the periods prior to certification, productivity change was driven mainly by technical change; whereas the source of productivity change after certification is mixed. However, prior to awards, productivity change was driven mainly by relative efficiency change, whereas post‐award productivity change was due to technical change. The results suggest that management focus on attaining certification did generate conceptual learning (linked to technical change) during the period leading to certification, but these effects were not significant after certification. The results also suggest that the TQM programs generated significant productivity gains in the long run, although setting the associated systems in place did not result in significant productivity change prior to winning awards. Thus, the study provides direct but nuanced evidence linking quality certification as well as the adoption of TQM programs to the associated conceptual and operational learning processes and their impact on the change in productivity.     

Introduction to Special Issue on POM Research on Emerging Markets

This special issue presents production and operations management research papers from emerging markets worldwide, focusing on their unique contexts, institutions and markets. Collectively, they offer insights into the unique operations management strategies and practices that firms face in emerging markets. The magnitude and pace of change is staggering. As a result, execution and managing growth in these emerging markets represents both huge operational and supply chain risks, and simultaneously vast opportunities. We are confident that these papers stimulate new operations management research while highlighting the effective use of different research methodologies. We welcome you to enjoy this special issue of POMS. We express our deep gratitude to editorial team for their support. We especially wish to thank the authors for their contributions to this special issue.     

A comparison of confidence regions and designs in estimation of a ratio

A computer simulation is performed to compare confidence regions arising from Fie1ler's theorem and approximate large sample intervals in estimating the point of extremum in quadratic regression. In addition, two designs, one of which is motivated by optimal design theory, are compared. These comparisons are made by examining the confidence level and accuracy of the regions, as well as the concentration of the standard point estimator, in a variety of settings. The results have implications for the more general problem of estimating a ratio of linear combinations in the general linear model.