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Activity Number: 497
Type: Contributed
Date/Time: Wednesday, August 7, 2013 : 8:30 AM to 10:20 AM
Sponsor: WNAR
Abstract - #308876
Title: Analyzing Left-Censored Outcomes in the Presence of Nonignorable Dropout
Author(s): Samantha MaWhinney*+ and Xinshuo M Wang and Jeri Forster and Marci Sontag
Companies: Colorado School of Public Health and Colorado School of Public Health and Colorado School of Public Health and Colorado School of Public Health
Keywords: Left-censoring ; Nonignorable dropout ; Varying-coefficient Models ; HIV
Abstract:

HIV clinical trials and longitudinal cohort studies often use HIV viral load as a measure of treatment efficacy. Treating HIV viral load as a continuous outcome can result in bias due to the lower quantification limits of the virologic assay. In addition, nonignorable dropout may also be suspected. We propose a model which utilizes a likelihood modified for the left censoring, while incorporating a B-spline varying-coefficient approach to accommodate nonignorable dropout. The method is implemented using the NLMIXED procedure in SAS. Results from simulation studies will be presented.


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