Browsing by Subject "Longitudinal"
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Item Comparing crossing hazard rate functions by joint modeling survival and longitudinal data(2013-06) Park, Ka YoungComparison of two hazard rate functions is important for evaluating treatment effect in studies concerning times to some important events. In practice, it is quite common that the two hazard rate functions cross each other at one or more unknown time points, representing temporal changes of the treatment effect. In certain applications, besides survival data, we also have related longitudinal data available regarding some time-dependent covariates. In such cases, a joint model that accommodates both types of data can allow us to infer the association between the survival and longitudinal data and to better assess the treatment effect. In our research, we propose a modeling approach for comparing two crossing hazard rate functions by joint modeling survival and longitudinal data. Maximum likelihood estimation is used in estimating the parameters of the proposed joint model using the EM algorithm. Asymptotic properties of the maximum likelihood estimators are studied. To illustrate the virtues of the proposed method, we compare the performance of the proposed method with several existing methods in a simulation study. Our proposed method is also demonstrated using a real dataset obtained from a HIV clinical trial. Furthermore, when jointly modeling the survival and longitudinal data in such cases, model selection and model diagnostics are especially important to provide reliable statistical analysis of the data. Therefore, we discuss several criteria for assessing model fit that have been used for model selection, and apply them to a joint modeling approach for comparing two crossing hazard rate functions when both survival and longitudinal data are available. Also, we propose both formal and informal methods for model assessment of the joint modeling approach. Our proposed methods are validated by a simulation study, and they are demonstrated by a real-data example concerning early breast cancer treatments.Item Sensory Features in Autism Spectrum Disorder: A Systematic Review of Measurement Quality and Empirical Investigation of Sensory Responsivity in Children at High and Low Familial Risk for Autism(2021-12) Gunderson, JaclynAutism spectrum disorder (ASD) is a complex neurodevelopmental disorder with heterogenous presentation and varying outcomes for children impacted by the condition. The etiology and bio-mechanisms of autism are not well understood. For decades research has focused on the social, communication, and cognitive symptoms associated with ASD. However, sensory symptoms were added to the diagnostic criteria for ASD in 2013 and continue to gain research attention. Historically, sensory symptoms were thought to emerge as secondary consequences of social-cognitive deficits. However, recent empirical work suggests that sensory symptoms manifest early in development and may contribute to the heterogeneity of ASD. For this dissertation, I systematically reviewed the literature to appraise the quality of proxy report sensory measurement tools used to assess sensory features in ASD. Furthermore, in a sample of children with a high and low familial likelihood for developing ASD, I characterized sensory responsivity in social and non-social contexts early in life and investigated the development of sensory responsivity throughout childhood with considerations for variables that may relate to developmental changes and their association with later adaptive behavior. Results from the current studies indicate that proxy report sensory questionnaires attempt to quantify sensory features in ASD via vastly different dimensions with little attention given to either construct or structural validity. Moreover, results show that sensory responsivity behaviors emerged across social and non-social contextual domains early in life and relate to restricted and repetitive behavior and adaptive behavior later in toddlerhood. Compared to children without ASD, children with ASD tend to demonstrate more early sensory responsivity behaviors that increase in a curvilinear relation to chronological age with specific trajectory differences across responsivity behavior patterns (hyperresponsivity, hyporesponsivity, sensory seeking). Additionally, heightened hyporesponsivity in the first year of life predicts lower adaptive behavior later in childhood. Specifically, results suggest that sensory features emerge prior to the consolidation of broad ASD symptoms and relate to adaptive outcomes. However, construct dimensions including the un-agreed upon multidimensionality of sensory features has important implications for future understanding and clinical practice.