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2002a), “Statistical Analysis of a Telephone Call Center: A Queueing Science Perspective,” technical report, University of Pennsylvania, downloadable at http://iew3.technion.ac.il/serveng/References/references.html
"... A call center is a service network in which agents provide telephonebased services. Customers who seek these services are delayed in telequeues. This article summarizes an analysis of a unique record of call center operations. The data comprise a complete operational history of a small banking cal ..."
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A call center is a service network in which agents provide telephonebased services. Customers who seek these services are delayed in telequeues. This article summarizes an analysis of a unique record of call center operations. The data comprise a complete operational history of a small banking call center, call by call, over a full year. Taking the perspective of queueing theory, we decompose the service process into three fundamental components: arrivals, customer patience, and service durations. Each component involves different basic mathematical structures and requires a different style of statistical analysis. Some of the key empirical results are sketched, along with descriptions of the varied techniques required. Several statistical techniques are developed for analysis of the basic components. One of these techniques is a test that a point process is a Poisson process. Another involves estimation of the mean function in a nonparametric regression with lognormal errors. A new graphical technique is introduced for nonparametric hazard rate estimation with censored data. Models are developed and implemented for forecasting of Poisson arrival rates. Finally, the article surveys how the characteristics deduced from the statistical analyses form the building blocks for theoretically interesting and practically useful mathematical models for call center operations.
Inequality in Life Spans and Mortality Convergence Across Industrialized Countries
, 2005
"... The second half of the twentieth century witnessed much convergence in life expectancy around the world. Closer inspection of mortality trends in advanced countries reveals that inequality in adult life spans, which we measure with the standard deviation of ages at death above age 10, S10, is increa ..."
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The second half of the twentieth century witnessed much convergence in life expectancy around the world. Closer inspection of mortality trends in advanced countries reveals that inequality in adult life spans, which we measure with the standard deviation of ages at death above age 10, S10, is increasingly responsible for the remaining divergence in mortality. We report striking differences in level and trend of S10 across industrialized countries since 1960, which cannot be explained by aggregate socioeconomic inequality or differential externalcause mortality. Rather, S10 reflects both within and betweengroup inequalities in life spans and conveys new information about their combined magnitudes and trends. These findings suggest that the challenge for health policies in this century is to reduce inequality, not just lengthen life. The human condition has improved tremendously during the course of modern development. At the beginning of the nineteenth century, life expectancy at birth, e0, hovered between 25 to 40 years (Maddison, 2001). Industrialization and unprecedented growth in percapita incomes coincided with significant gains in e0, which by 1960 reached roughly 70 years among
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, 2005
"... The second half of the twentieth century witnessed much convergence in life expectancy around the world. We examine differences in the age pattern of mortality between countries over time to show that inequality in adult life spans, which we measure with the standard deviation of life table ages at ..."
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The second half of the twentieth century witnessed much convergence in life expectancy around the world. We examine differences in the age pattern of mortality between countries over time to show that inequality in adult life spans, which we measure with the standard deviation of life table ages at death above age 10, S10, is increasingly responsible for the remaining divergence in mortality. We report striking differences in level and trend of S10 across industrialized countries since 1960, which cannot be explained by aggregate socioeconomic inequality or differential externalcause mortality. Rather, S10 reflects both within and betweengroup inequalities in life spans and conveys new information about their combined magnitudes and trends. These findings suggest that the challenge for health policies in this century is to reduce inequality, not just lengthen life.
Inference on Parameters of a Shifted and Rescaled Wiener Process Based on Nonidentically Distributed Observations
"... Abstract. The paper deals with inference about the parameters a and b2 of the random process {bwt + at; t ≥ 0}, where {wt; t ≥ 0} is the Wiener process, a ≥ 0 and b2> 0. Inference is based on the first time when the process reaches a prespecified positive boundary, where the boundary can be diff ..."
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Abstract. The paper deals with inference about the parameters a and b2 of the random process {bwt + at; t ≥ 0}, where {wt; t ≥ 0} is the Wiener process, a ≥ 0 and b2> 0. Inference is based on the first time when the process reaches a prespecified positive boundary, where the boundary can be different for each observation. We focus on estimation and we shortly deal with testing hypotheses about one parameter at a time. We will show that neither the variance of estimators, nor the power of tests depend on the choice of the boundaries. These characteristics only depend on the number of observations and on the sum of the boundaries.