Showing papers by "Gong Tang published in 2007"
TL;DR: It is shown that accounting for the nature of the dropout process influences results and that sensitivity analysis is useful in assessing the robustness of parameter estimates and related uncertainties, and it is recommended to perform a sensitivity analysis when the exact nature ofthe drop out process cannot be discerned.
47 citations
TL;DR: This report illustrates the usage of OSWALD for analyzing longitudinal data with dropouts and how to draw appropriate conclusions based on the analytic results under different assumptions regarding the dropout mechanism.
7 citations
TL;DR: In this article, the authors proposed a method using partial residuals to fit generalized additive models (GAMs) in the presence of concurvity and called it the "partial regression" method.
Abstract: Generalized additive models (GAMs) have been used as a standard analytic tool in studies of air pollution and health during the last decade. The air pollution measure is usually assumed to be linearly related to the health indicator and the effects of other covariates are modeled through smooth functions. A major statistical concern is the appropriateness of fitting GAMs in the presence of concurvity. Generalized linear models (GLM) with natural cubic splines as smoothers (GLM + NS) have been shown to perform better than GAM with smoothing splines (GAM + S), in regard to the bias and variance estimates using standard model fitting methods. As nonparametric smoothers are attractive for their flexibility and easy implementation, search for alternative methods to fit GAM + S is warranted. In this article, we propose a method using partial residuals to fit GAM + S and call it the “partial regression” method. Simulation results indicate better performance of the proposed method compared to gam.exact function in S-plus, the standard tool in air pollution studies, in regard to bias and variance estimates. In addition, the proposed method is less sensitive to the degree of smoothing and accommodates asymmetric smoothers. Copyright © 2007 John Wiley & Sons, Ltd.
4 citations
TL;DR: This study examined interaction between the test and chemotherapy in the B20 trial and identified high and low risk groups that both showed significant improvement upon treatment with cytotox...
Abstract: 529 Background: We previously reported the association between a five monoclonal antibody test staining p53, NDRG1, SLC7A5, CEACAM5 and HTF9C and recurrence-free interval (RFI) in 711 ER+ N- breast cancer patients from Tamoxifen (Tam) arm of the NSABP trials B14 and B20 (SABCS 2006). In this study, we examined interaction between the test and chemotherapy in the B20 trial. Subjects and Methods: Tissue array sections from B20 paraffin blocks were stained using standard IHC protocols (N=457). Pre-defined scoring rules and cut- points were applied. RFI was defined as time from entry to any local, regional or distant recurrence. Log-rank test was applied to assess the effect of chemotherapy for each risk stratum pre-defined by this IHC test. Interaction between risk strata and treatment was assessed by the likelihood ratio test in a Cox model with age and clinical tumor size adjusted. Results: The IHC test identified high and low risk groups that both showed significant improvement upon treatment with cytotox...
3 citations