Main content

Survival Analysis with Internal Categorical Time-varying Covariates

Show simple item record

dc.contributor.advisor Horrocks, Julie
dc.contributor.advisor Darlington, Gerarda A. Keown-Stoneman, Charles D.G. 2017-08-16T14:12:17Z 2017-08-16T14:12:17Z 2017-05 2017-05-15 2017-08-16
dc.description.abstract In the study of time-to-event data, an important feature is the ability to include time-varying covariates. Concerns have been raised over the use of Cox models in the presence of internal time-varying covariates. Multi-state models have been proposed as an acceptable alternative approach for internal time-varying covariates. A motivating example throughout this thesis is the development of bipolar disorder. It has been proposed that bipolar disorder progresses in a predictable sequence of clinical stages. In Chapter 2 the objective is to compare Cox models and non-parametric multi-state models in the presence of other psychiatric diagnoses. These diagnoses are coded as binary time-varying covariates in a Cox model or as states in a non-parametric multi-state model. A common assumption in Cox models with time-varying covariates is that the effect of a covariate on the event of interest is constant and permanent after it has changed. Chapter 3 presents a modification to the usual Cox model for binary time-varying covariates that allows the influence of a covariate to exponentially decay over time. Methods for generating data using the inverse cumulative density function for the proposed model are developed. Likelihood ratio tests and AIC are investigated as methods for comparing the proposed model with the commonly used permanent exposure model. A simulation study is performed and three different example data analyses are presented. One advantage to parametric multi-state models is the inclusion of misclassification. Until now, this approach has largely been confined to exponential waiting times within each state. In Chapter 4 we introduce Bayesian parametric multi-state models with unknown misclassification of states and Weibull distributed waiting times between states. Weibull waiting times allow transitions between states to depend on the time spent in the current state, a feature lacking in exponential waiting times. To fit the proposed Bayesian model, a Markov chain Monte Carlo (MCMC) Metropolis-Hastings algorithm is employed. The motivating example on the progression of bipolar disorder is presented along with simulation results. From the example analysis, there is evidence that assuming Weibull waiting times is an improvement over assuming exponential waiting times in the study of bipolar disorder. en_US
dc.language.iso en en_US
dc.rights Attribution-NonCommercial-NoDerivs 2.5 Canada *
dc.rights.uri *
dc.subject multi-state models en_US
dc.subject survival analysis en_US
dc.subject Cox models en_US
dc.subject statistics en_US
dc.title Survival Analysis with Internal Categorical Time-varying Covariates en_US
dc.type Thesis en_US Mathematics and Statistics en_US Doctor of Philosophy en_US Department of Mathematics and Statistics en_US

Files in this item

Files Size Format View Description
Keown-Stoneman_Charles_201708_PhD.pdf 2.575Mb PDF View/Open Main Thesis

This item appears in the following Collection(s)

Show simple item record

Attribution-NonCommercial-NoDerivs 2.5 Canada Except where otherwise noted, this item's license is described as Attribution-NonCommercial-NoDerivs 2.5 Canada