Showing papers by "Robert Tibshirani published in 1990"
TL;DR: An exploratory technique for investigating the nature of covariate effects in Cox's proportional hazards model features an additive term fj(chi ij), in place of the usual linear term sigma p1 chi ij beta j, where chi i1, chi i2,...,chi ip are covariate values for the ith individual.
Abstract: We discuss an exploratory technique for investigating the nature of covariate effects in Cox's proportional hazards model. This technique features an additive term sigma p1 fj(chi ij), in place of the usual linear term sigma p1 chi ij beta j, where chi i1, chi i2,...,chi ip are covariate values for the ith individual. The fj(.) are unspecified smooth functions that are estimated using scatterplot smoothers. These functions can be used for descriptive purposes or to suggest transformations of the covariates. The estimation technique is a variation of the local scoring algorithm for generalized additive models (Hastie and Tibshirani, 1986, Statistical Science 1, 297-318).
242 citations
TL;DR: In this article, a simple adjustment for profile likelihoods is proposed to alleviate some of the problems inherent in the use of profile likelihood, such as bias, inconsistency and overoptimistic variance estimates.
Abstract: SUMMARY We propose a simple adjustment for profile likelihoods. The aim of the adjustment is to alleviate some of the problems inherent in the use of profile likelihoods, such as bias, inconsistency and overoptimistic variance estimates. The adjustment is applied to the profile loglikelihood score function at each parameter value so that its mean is zero and its variance is the negative expected derivative matrix of the adjusted score function. For cases in which explicit calculation of the adjustments is difficult, we give two methods to simplify their computation: an 'automatic' simulation method that requires as input only the profile loglikelihood and its first few derivatives; first-order asymptotic expressions. Some examples are provided and a comparison is made with the conditional profile log-likelihood of Cox and Reid.
213 citations
TL;DR: The decision with respect to the need for hospitalization in acute childhood asthma, is in practice based mainly on careful clinical evaluation, and Pulmonary function and SaO2 measurements, although helpful adjuncts in the assessment of acute asthma, do not appear to contribute to the identification of patients who need hospital admission.
92 citations
TL;DR: It is recommended that the avoidance of rapid myocardial cooling on bypass in all patients before induction of cardioplegic ischemic arrest is avoided, as patient diagnosis, weight, age, and age at operation were significant risk factors for operative mortality.
37 citations