Estimating the mean life time using right censored data

Estimation of the population mean based on right censored observations is considered. The naive sample mean will be an inconsistent and asymptotically biased estimator in this case. An estimate suggested in textbooks is to compute the area under a Kaplan–Meier curve. In this note, two more seemingly different approaches are introduced. Students’ reaction to these approaches was very positive in an introductory survival analysis course the author recently taught.     

Testing for a unit root in an arima(p,1,0) signal observed with ma(q) noise

An ARIMA(p,1,0) signal disturbed by MA(q) noise is an ARIMA(p,1, p+q+1) process restricted by nonlinear constraints on parameters. For this model with a unit root the restricted maximum likelihood estimator (RMLE) of the unit root is strongly consistent and it has the same limiting distribution as the ordinary least squares estimator of the unit root in an AR(1) model tabulated by Dickey and Fuller (1979). A modified RMLE is proposed which has the same limiting properties as the RMLE and is computationally much simpler. Simulation results show that our unit root tests based on the modified RMLE perform very well for small samples and compare favorably with the Said and Dickey (1985) tests with respect to both sizes and powers. An illustrative example from sample survey is given.     

Population trends and population policy in Ceylon

The population of Ceylon has many. features in common with other Asian countries. Ceylon has, however, the distinction of an unusual wealth of demographic data. The study of many problems of general interest to Asia may thus be made for Ceylon, and the conclusions in part extended to other Asian countries.     

‘Ch'us mon propre Bescherelle’: Challenges from the Hip‐Hop nation to the Quebec nation1

We examine the uses of and attitudes towards language of members of the Montreal Hip‐Hop community in relation to Quebec language‐in‐education policies. These policies, implemented in the 1970s, have ensured that French has become the common public language of an ethnically diverse young adult population in Montreal. We argue, using Blommaert's (2005) model of orders of indexicality, that the dominant language hierarchy orders established by government policy have been both flattened and reordered by members of the Montreal Hip‐Hop community, whose multilingual lyrics insist: (1) that while French is the lingua franca, it is a much more inclusive category which includes ‘Bad French,’ regional and class dialects, and European French; and (2) that all languages spoken by community members are valuable as linguistic resources for creativity and communication with multiple audiences. We draw from a database which includes interviews with and lyrics from rappers of Haitian, Latin‐American, African‐American and Québécois origin.     

Distressed Selling by Farmers: Model,Analysis, and Use in Policy‐Making

Among the various governmental schemes that support agriculture, support prices have been adopted by many developing countries. A support price for an agricultural crop is a guaranteed price at which a governmental entity agrees to purchase that crop from farmers. Despite this surety, a surprising practice of “distressed” selling 1 1 A 1‐minute news clip on distressed selling is available at: https://www.youtube.com/watch?v=U2lr5rBTpaU
has been widely observed in practice: Farmers sell a significant portion of their crops to outside agents at prices much lower than the support price. We build a tractable stochastic dynamic programming model that captures the salient features of the ground realities—limited as well as uncertain procurement capacity, high holding costs for the farmers, and lack of affordable credit—that conspire to induce distressed selling and, consequently, a significant loss of welfare of the farmers. Using real data on procurement under a support‐price program, we establish the accuracy of our model's prediction on the volume of distressed sales. Finally, we show how our model and its solution can serve as a simple and useful tool for policy‐makers to assess the relative impact of the improvements in the main determinants of distressed sales.     

An ergonomic study on the onset of mental fatigue among the load handling workers of a central market area in Kolkata

It is a well recognized fact that manual material handling (MMH) entails enormous physical labor and associated discomfort feeling, which invariably culminate into musculoskeletal disorders. However mental fatigue, in such instances, becomes an unexplored parameter that needs definite attention during assessment of work status of MMH workers. The present study is being performed among 75 porters of a central market in Kolkata to ascertain the extent of physical and mental exhaustion among them. SF-12 health status questionnaire followed by another questionnaire involving psychosocial questions were performed among them. The analysis of both the questionnaires clearly revealed that most of the porters are under severe physical exertion as they alone carry about 120 kg load at a time and such activity is repeated at least 40 times throughout the day. They always suffer from pain and discomfort feeling at different body parts and this interferes with their normal work activity to a great extent. Moreover absenteeism means no financial return and even a day's rigourous work fetches meagre income. The inability to support family convincingly even after performing such hazardous tasks makes them feel low. Monotony, boredom, fatigue and mental trauma form an integral part of their daily work schedule.     

WHY DOES CHILD LABOR PERSIST WITH DECLINING POVERTY?

We develop a dynamic overlapping generations model to highlight the role of income inequality in explaining the persistence of child labor under declining poverty. Differential investment in two forms of human capital—schooling and health—in the presence of inequality gives rise to a nonconvergent income distribution in the steady state characterized by multiple steady states of relative income with varying levels of education, health, and child labor. The child labor trap thus generated is shown to preserve itself despite rising per capita income. Policy recommendations include public provision of education targeted toward reducing schooling costs for the poor or raising the efficacy of public health infrastructure. (JEL I1, J2, O1, O2)     

Processes Underlying Interfirm Cooperation

This special issue intended to bring together scholarly insights on the processes that underlie the formation, growth, management and termination of interfirm cooperation (IFC). In this introductory paper, we highlight what we know about IFC and why fresh perspectives are warranted on this phenomenon from a conceptual and practical standpoint. We also highlight the contribution of each paper published in this special issue. The seven selected papers differ in their theoretical perspective, context, research methodology and findings, but collectively they enhance our understanding of various IFC processes. We end this paper by highlighting fertile avenues of future research.     

Two-stage stepup procedures controlling FDR

A two-stage stepup procedure is defined and an explicit formula for the FDR of this procedure is derived under any distributional setting. Sets of critical values are determined that provide a control of the FDR of a two-stage stepup procedure under iid mixture model. A class of two-stage FDR procedures modifying the Benjamini–Hochberg (BH) procedure and containing the one given in Storey et al. [2004. Strong control, conservative point estimation and simultanaeous conservative consistency of false discovery rates: a unified approach. J. Roy. Statist. Soc. Ser. B 66, 187–205] is obtained. The FDR controlling property of the Storey–Taylor–Siegmund procedure is proved only under the independence, which is different from that presented by these authors. A single-stage stepup procedure controlling the FDR under any form of dependence, which is different from and in some situations performs better than the Benjamini–Yekutieli (BY) procedure, is given before discussing how to obtain two-stage versions of the BY and this new procedures. Simulations reveal that procedures proposed in this article under the mixture model can perform quite well in terms of improving the FDR control of the BH procedure. However, the similar idea of improving the FDR control of a stepup procedure under any form dependence does not seem to work.     

Regeneration-based bootstrap for Markov chains

We consider a bootstrap method for Markov chains where the original chain is broken into a (random) number of cycles based on an atom (regeneration point) and the bootstrap scheme resamples from these cycles. We investigate the asymptotic accuracy of this method for the case of a sum (or a sample mean) related to the Markov chain. Under some standard moment conditions, the method is shown to be at least as good as the normal approximation, and better (second-order accurate) in the case of nonlattice summands. We give three examples to illustrate the applicability of our results.