title: A semiparametric pseudo-score method for analysis of two-phase studies with continuous phase-I covariates.
abstract: Two-phase study designs can reduce cost and other practical burdens associated with large scale epidemiologic studies by limiting ascertainment of expensive covariates to a smaller but informative sub-sample (phase-II) of the main study (phase-I). During the analysis of such studies, however, subjects who are selected at phase-I but not at phase-II, remain informative as they may have partial covariate information. A variety of semi-parametric methods now exist for incorporating such data from phase-I subjects when the covariate information can be summarized into a finite number of strata. In this article, we consider extending the pseudo-score approach proposed by Chatterjee et al. (J Am Stat Assoc 98:158-168, 2003) using a kernel smoothing approach to incorporate information on continuous phase-I covariates. Practical issues and algorithms for implementing the methods using existing software are discussed. A sandwich-type variance estimator based on the influence function representation of the pseudo-score function is proposed. Finite sample performance of the methods are studies using simulated data. Advantage of the proposed smoothing approach over alternative methods that use discretized phase-I covariate information is illustrated using two-phase data simulated within the National Wilms Tumor Study (NWTS).
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, DHHS, Rockville, MD 20852, USA. chattern@mail.nih.gov
authors.forename: Nilanjan
authors.initials: N
authors.lastname: Chatterjee
authors.forename: Yi-Hau
authors.initials: YH
authors.lastname: Chen
mesh_terms: D016022:Case-Control Studies; D015331:Cohort Studies; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D015340:Epidemiologic Research Design; D006801:Humans; D007680:Kidney Neoplasms / Q000453:epidemiology / Q000628:therapy; D009364:Neoplasm Recurrence, Local / Q000453:epidemiology; D012044:Regression Analysis; D009396:Wilms Tumor / Q000453:epidemiology / Q000628:therapy