Diagnostics For Mixture Regression Models: Applications To Public Health
Funder
National Health and Medical Research Council
Funding Amount
$128,250.00
Summary
In many public health studies, finite mixture regression models are often used to analyse data arising from heterogeneous populations. It is important to assess the stability of parameter estimates and the validity of statistical inferences when the underlying assumptions appear to be violated, but appropriate diagnostics are lacking in the literature. This research aims to develop effective diagnostic methods for assessing the adequacy of mixture regression models and the sensitivity of accompa ....In many public health studies, finite mixture regression models are often used to analyse data arising from heterogeneous populations. It is important to assess the stability of parameter estimates and the validity of statistical inferences when the underlying assumptions appear to be violated, but appropriate diagnostics are lacking in the literature. This research aims to develop effective diagnostic methods for assessing the adequacy of mixture regression models and the sensitivity of accompanying test statistics. The methodology developed will enable health care professionals to focus on substantive issues and to draw accurate and valid conclusions inferred from correlated and over-dispersed outcomes. In the presence of anomalous observations, the influence diagnostics can provide insights into the source of heterogeneity and the apparent over-dispersion, while accommodating the inherent correlation due to the longitudinal study design or nested data structure. Significance of the research lies in its scientific novelty and the breadth of its practical applications. The benefits to public health will accrue both nationally and internationally. For the empirical studies that motivated and are linked to this research, evaluation of health outcomes has significant implications in the prevention and control of recurrent urinary tract infections, hospital strategic planning, and post-stroke care and rehabilitation management. Moreover, appropriate assessment of a physical activity intervention for older adults is pertinent to falls prevention and reduction of musculoskeletal disorders among sedentary seniors.Read moreRead less
Hierarchical Finite Mixture Modelling Of Health Outcomes: A Risk-adjusted Random Effects Approach
Funder
National Health and Medical Research Council
Funding Amount
$117,000.00
Summary
In medical and health studies, finite mixture regression models have been used to analyze data arising from heterogeneous populations. Traditionally, the application of mixture models is mainly concerned with finite normal mixtures. Recent computational advances and methodological developments have enhanced the extension of the method to non-normal finite mixtures, such as the modelling of discrete responses in finite mixture of generalized linear models and overlapping phases of failure time da ....In medical and health studies, finite mixture regression models have been used to analyze data arising from heterogeneous populations. Traditionally, the application of mixture models is mainly concerned with finite normal mixtures. Recent computational advances and methodological developments have enhanced the extension of the method to non-normal finite mixtures, such as the modelling of discrete responses in finite mixture of generalized linear models and overlapping phases of failure time data in the context of survival analysis. However, due to the hierarchical study design or the data collection procedure, the inherent correlation structure and-or clustering effects present may contribute to extra variations and violation of the independence assumption, resulting in spurious associations and misleading inferences based on the finite mixture model. This project aims to present a unified approach to accommodate both heterogeneity and dependency of observations, by incorporating random effects into finite mixture regression models. The new methodology will provide an integrated framework to analyze heterogeneous and correlated health outcomes. Three empirical studies are considered, namely, evaluation of an occupational injury reduction intervention, length of hospital stay modeling, and analysis of survival times of patients after cardiac surgery. The long term benefits to bioscience are accurate and valid conclusions inferred from medical and health studies, as well as the correct identification of high-risk subgroups. For the three application areas of this project, the improved analyses will specifically enable the evaluation of a participatory ergonomics intervention, the assessment of hospital efficiency and factors influencing length of hospitalization, and the determination of effectiveness of treatments prescribed pre- and post- operation, respectively.Read moreRead less
Analysis Of HIV Virologic Response-rebound Data: Prognostic Indicators Of Post-HAART Viral Control
Funder
National Health and Medical Research Council
Funding Amount
$144,000.00
Summary
The introduction of potent anti-retroviral therapy into standard clinical management of HIV infected individuals has been associated with high rates of reduction in plasma viral loads over short periods of time. However, there remains considerable variation in the degree of longer-term viral control as a result of viral resistance, toxicity, timing of treatment initiation and choice of drug regimen. In particular, the most appropriate time to initiate treatment remains clouded, with the need to ....The introduction of potent anti-retroviral therapy into standard clinical management of HIV infected individuals has been associated with high rates of reduction in plasma viral loads over short periods of time. However, there remains considerable variation in the degree of longer-term viral control as a result of viral resistance, toxicity, timing of treatment initiation and choice of drug regimen. In particular, the most appropriate time to initiate treatment remains clouded, with the need to initiate treatment sufficiently early in order to avoid irreversible damage balanced by the problems of potential viral resistance or toxicity if started too soon. Determination of factors which will assist practitioners to optimise the timing of treatment initiation remains a high priority. Our aim in this project is to develop and study the use of novel statistical mixed-effects models designed to analyse factors associated with visit-time viral load data following commencement of therapy, taking account of the entire follow-up profiles of responses over time. The project involves both theoretical and empirical analyses of the estimation and inferential properties of the mixed-model method in conjunction with comprehensive analyses of prognostic factors associated with post-treatment virologic control in patients from the Western Australian HIV Cohort Study. These include demographic, virologic, immunologic, adherence and host genetic factors. The statistical methods developed will have wide applicability and add significantly to the suite of procedures available for the analysis of longitudinal response data.Read moreRead less
Statistical Methods To Assist The Control Of Communicable Diseases, And Their Application
Funder
National Health and Medical Research Council
Funding Amount
$211,527.00
Summary
A range of programs, such as vaccination schedules and intervention in outbreaks, is in place to reduce our burden of illness from infectious diseases. This project aims to develop new methods, based on models and associated statistical analyses, to help ensure that our control programs are based on the best available evidence. There are five specific themes: 1. Developed methods for predicting major outbreaks of diseases and appy them to Australian data on measles, pertussis and Ross River viru ....A range of programs, such as vaccination schedules and intervention in outbreaks, is in place to reduce our burden of illness from infectious diseases. This project aims to develop new methods, based on models and associated statistical analyses, to help ensure that our control programs are based on the best available evidence. There are five specific themes: 1. Developed methods for predicting major outbreaks of diseases and appy them to Australian data on measles, pertussis and Ross River virus. The new methods will enable timely intervention to reduce the population risk from these diseases, and to guide the proposed elimination of measles from Australia. 2. The current concept of vaccine efficacy, which is central to the epidemiological assessment of vaccines, performs poorly when the vaccine provides only partial protection, when immunity wanes over time and when infected vaccinees have a lower infectivity. A concept of vaccine efficacy will be developed that overcomes these weaknesses. This concept will find widespread use in epidemiology. 3. Data available from 80 outbreak investigations of transmissible diseases will be analysed to assess the relative effectiveness of various intervention steps. 4. A comprehensive model, and associated computer software, will be developed as a tool for assessing the relative merits of different vaccination schedules. It will be applied to address Australian policy issues for vaccination against pertussis, chickenpox and rubella. 5. The method of backprojection for estimating trends in HIV infection and predicting AIDS incidence will be enhanced to incorporate newly available data in which HIV and AIDS diagnoses are linked. This will enable a precise assessment of infection incidence among heterosexuals and other exposure categories with relatively few cases, to ensure that HIV does not spread more widely.Read moreRead less