A Predictive Study of Dirichlet Process Mixture Models for Curve Fitting

This paper examines the use of Dirichlet process mixtures for curve fitting. An important modelling aspect in this setting is the choice between constant and covariate‐dependent weights. By examining the problem of curve fitting from a predictive perspective, we show the advantages of using covariate‐dependent weights. These advantages are a result of the incorporation of covariate proximity in the latent partition. However, closer examination of the partition yields further complications, which arise from the vast number of total partitions. To overcome this, we propose to modify the probability law of the random partition to strictly enforce the notion of covariate proximity, while still maintaining certain properties of the Dirichlet process. This allows the distribution of the partition to depend on the covariate in a simple manner and greatly reduces the total number of possible partitions, resulting in improved curve fitting and faster computations. Numerical illustrations are presented.     

Age-related neurodegenerative changes and how they affect the gut

The enteric nervous system (ENS) is the division of the autonomic nervous system that regulates gastrointestinal (GI) function. Although large numbers of enteric neurons may be lost with age, the GI tract remains surprisingly functional. Exceptions to this generality include swallowing disorders and reduced colonic motility in the elderly. Evidence of age-related neurodegenerative changes in structure and function of the ENS is briefly reviewed in this Perspective.     

Marital transitions and mental health

Most research identifies marital disruption as a precursor for poor mental health but is generally unable to discount the potential selection effect of poor mental health leading to marital disruption. We use data from nine annual waves of the British Household Panel Survey to examine social selection and social causation as competing explanations. Mental health is measured using the general health questionnaire. We examine mental health at multiple time points prior to and after a marital transition through separation or divorce and compare this process to those who experience widowhood. All groups transitioning out of marriage have a higher prevalence of poor mental health afterwards but for those separated or divorced, poor mental health also precedes marital disruption, lending support to both social-causation and social-selection processes. The processes both preceding and after the transition to widowhood differ, with increased prevalence of disorder centering around the time surrounding the death itself     

Racial residential segregation in the sun belt

In recent years demographic researchers have devoted considerable attention to two topics: (1) migration to the sun belt and (2) racial and economic transformation of neighborhoods. This study addresses both, and develops a theoretical and analytical model to test the relationship of intra-urban and inter-urban migration patterns as they relate to race and social class. The study measures and analyzes patterns of racial and economic transition in neighborhoods for two Oklahoma SMSAs. Comparisons are made between differential degrees of residential segregation accounted for by in-migrants, utilizing U.S. Census tracts for 1970 and 1980. The model, once specified and evaluated, demonstrates that patterns and factors traditionally associated with residential segregation may have less relevance forsun belt cities in the coming decades.