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492
Social Networks and Employee Performance in a Call Center
 American Journal of Sociology
, 2005
"... Much research in sociology and labor economics studies proxies for productivity; consequently, little is known about the relationship between personal contacts and worker performance. This study addresses, for the first time, the role of referral contacts on workers’ performance. Using employees ’ ..."
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Much research in sociology and labor economics studies proxies for productivity; consequently, little is known about the relationship between personal contacts and worker performance. This study addresses, for the first time, the role of referral contacts on workers’ performance. Using employees ’ hiring and performance data in a call center, the author examines the performance implications over time of hiring new workers via employee referrals. When assessing whether referrals are more productive than nonreferrals, the author also considers the relationship between employee productivity and turnover. This study finds that referrals are initially more productive than nonreferrals, but longitudinal analyses emphasize posthire social processes among socially connected employees. This article demonstrates that the effect of referral ties continues beyond the hiring process, having longterm effects on employee attachment to the firm and on performance. For decades, we have seen a stream of theoretical and empirical studies in economic sociology and labor economics examining how recruitment sources relate to employees ’ outcomes such as turnover and tenure, starting wages, and wage growth (for a detailed review of these studies, see 1 I am grateful for the financial support provided by the Social Sciences Research Council (Program of the Corporation as a Social Institution). I have benefited enormously from the extensive and detailed comments of Roberto M. Fernández, Mark
Statistical issues in the design, analysis and interpretation of animal carcinogenicity studies. Environ Health Persp 58: 385−392
, 1984
"... Statistical issues in the design, analysis and interpretation of animal carcinogenicity studies are discussed. In the area of experimental design, issues that must be considered include randomization of animals, sample size considerations, dose selection and allocation of animals to experimental gro ..."
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Statistical issues in the design, analysis and interpretation of animal carcinogenicity studies are discussed. In the area of experimental design, issues that must be considered include randomization of animals, sample size considerations, dose selection and allocation of animals to experimental groups, and control of potentially confounding factors. In the analysis of tumor incidence data, survival differences among groups should be taken into account. It is important to try to distinguish between tumors that contribute to the death of the animal and "incidental " tumors discovered at autopsy in an animal dying of an unrelated cause. Life table analyses (appropriate for lethal tumors) and incidental tumor tests (appropriate for nonfatal tumors) are described, and the utilization of these procedures by the National Tbxicology Program is discussed. Despite the fact that past interpretations of carcinogenicity data have tended to focus on pairwise comparisons in general and highdose effects in particular, the importance of trend tests should not be overlooked, since these procedures are more sensitive than pairwise comparisons to the detection of carcinogenic effects. No rigid statistical "decision rule " should be employed in the interpretation of carcinogenicity data. Although the statistical significance of an observed tumor increase is perhaps the single most important piece of evidence used in the evaluation process, a number of biological factors must also be taken into account. The use of historical control data, the falsepositive issue and the interpretation of negative trends are also discussed.
Bayesian Variable Selection for Proportional Hazards Models
, 1996
"... The authors consider the problem of Bayesian variable selection for proportional hazards regression models with right censored data. They propose a semiparametric approach in which a nonparametric prior is specified for the baseline hazard rate and a fully parametric prior is specified for the regr ..."
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Cited by 17 (1 self)
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The authors consider the problem of Bayesian variable selection for proportional hazards regression models with right censored data. They propose a semiparametric approach in which a nonparametric prior is specified for the baseline hazard rate and a fully parametric prior is specified for the regression coe#cients. For the baseline hazard, they use a discrete gamma process prior, and for the regression coe#cients and the model space, they propose a semiautomatic parametric informative prior specification that focuses on the observables rather than the parameters. To implement the methodology, they propose a Markov chain Monte Carlo method to compute the posterior model probabilities. Examples using simulated and real data are given to demonstrate the methodology. R ESUM E Les auteurs abordent d'un point de vue bayesien le problemedelaselection de variables dans les modeles de regression des risques proportionnels en presence de censure a droite. Ils proposent une approche semip...
Coronary Risk Prediction by Logical Analysis of Data
, 2002
"... The objective of this study was to distinguish within a population of patients with known or suspected coronary artery disease groups at high and at low mortality rates. The study was based on Cleveland Clinic Foundation's dataset of 9454 patients, of whom 312 died during an observation period ..."
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The objective of this study was to distinguish within a population of patients with known or suspected coronary artery disease groups at high and at low mortality rates. The study was based on Cleveland Clinic Foundation's dataset of 9454 patients, of whom 312 died during an observation period of 9 years. The Logical Analysis of Data method was adapted to handle the disproportioned size of the two groups of patients, and the inseparable character of this dataset  characteristic to many medical problems. As a result of the study, we have identified a highrisk group of patients representing 1/5 of the population, with a mortality rate 4 times higher than the average, and including 3/4 of the patients who died. The lowrisk group identified in the study, representing approximately 4/5 of the population, had a mortality rate 3 times lower than the average.
Asymptotics and the theory of inference
, 2003
"... Asymptotic analysis has always been very useful for deriving distributions in statistics in cases where the exact distribution is unavailable. More importantly, asymptotic analysis can also provide insight into the inference process itself, suggesting what information is available and how this infor ..."
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Asymptotic analysis has always been very useful for deriving distributions in statistics in cases where the exact distribution is unavailable. More importantly, asymptotic analysis can also provide insight into the inference process itself, suggesting what information is available and how this information may be extracted. The development of likelihood inference over the past twentysome years provides an illustration of the interplay between techniques of approximation and statistical theory.
Rate of Convergence for Hazard Regression
 Scand. J. Statist
, 1994
"... The logarithm of the conditional hazard function of a survival time given one or more covariates is approximated by a function having the form of a specified sum of functions of at most d of the variables. Subject to this form, the approximation is chosen to maximize the expected conditional logli ..."
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The logarithm of the conditional hazard function of a survival time given one or more covariates is approximated by a function having the form of a specified sum of functions of at most d of the variables. Subject to this form, the approximation is chosen to maximize the expected conditional loglikelihood. Maximum likelihood and sums of tensor products of polynomial splines are used to construct an estimate of this approximation based on a random sample. The components of this estimate possess a rate of convergence that depends only on d and a suitably defined smoothness parameter. KEY WORDS: Conditional hazard function; Maximum likelihood; Tensor product splines. This research was supported in part by a grant from the Graduate School Fund of the University of Washington. y This research was supported in part by National Science Foundation Grant DMS9204247 z This research was supported in part by a Research Council Grant from the University of North Carolina. 1 1. Introducti...
The Role of Frailty Models and Accelerated Failure Time Models in Describing Heterogeneity Due to Omitted Covariates
, 1997
"... INTRODUCTION Statistical modelling of heterogeneity may be based on strati#cation according to factors, regression on covariates, or by assuming a probability distribution of the interindividual variation. In survival analysis Vaupel et al. coined the phrase #frailty" in connection with a par ..."
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Cited by 15 (0 self)
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INTRODUCTION Statistical modelling of heterogeneity may be based on strati#cation according to factors, regression on covariates, or by assuming a probability distribution of the interindividual variation. In survival analysis Vaupel et al. coined the phrase #frailty" in connection with a particular version of such a stochastic model, in which individual i was assumed to have death intensity Z i ##a# at age a, where the random variable Z i #the #frailty"# is assumed to have a gamma distribution. The assumptions that the randomness is ageindependent and that it acts multiplicatively on an underlying intensity ##a# are in principle arbitrary but have been taken as the basis for much subsequent work on random heterogeneity in survival analysis. Useful surveys are by Andersen et al. , Chapter IX, Nielsen et al. , Klein et al. , Aalen Schumacher et al. and Hougaard . The frailty models are likely to be particularly useful for modelling multivariate survival times, whethe
Heart rate recovery immediately after treadmill exercise and left ventricular systolic dysfunction as predictors of mortality: the case of stress echocardiography. Circulation
"... The online version of this article, along with updated information and services, is located on the ..."
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The online version of this article, along with updated information and services, is located on the
Mixed modelbased hazard estimation
 Journal of Computational and Graphical Statistics
, 2002
"... We propose a new method for estimation of the hazard function from a set of censored failure time data, with a view to extending the general approach to more complicated models. The approach is based on a mixed model representation of penalized spline hazard estimators. One payoff is the automation ..."
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We propose a new method for estimation of the hazard function from a set of censored failure time data, with a view to extending the general approach to more complicated models. The approach is based on a mixed model representation of penalized spline hazard estimators. One payoff is the automation of the smoothing parameter choice through restricted maximum likelihood. Another is the option to use standard mixed model software for automatic hazard estimation. Key words: Nonparametric regression; Restricted maximum likelihood; Variance component; Survival analysis.
Deficiency of either cyclooxygenase (COX)1 or COX2 alters epidermal differentiation and reduces mouse skin tumorigenesis
 Cancer Res
, 2002
"... This article cites 42 articles, 24 of which you can access for free at: ..."
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This article cites 42 articles, 24 of which you can access for free at: