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Abstract
Slower gait speed has previously been shown to be associated with mortality in aging pop- ulations, based on a single measure of gait speed,1–3 but repeated measures of gait speed may be more informative. Although an extended Cox model can accommodate a time- varying covariate, the Cox framework has certain limitations in context of endogenous or continuous time-varying covariates or time-varying covariates measured with error. The joint modeling framework uses a smooth, continuous model of the time-varying co- variate that may more accurately represent its true, underlying longitudinal trajectory. The objective of this thesis is to estimate the association between longitudinal trajectories of gait speed and survival time and to compare estimates of association from separate models (i.e., mixed-effects models and Cox models) and joint models.