Semiparametric Bayesian classification with longitudinal markers

Summary.  We analyse data from a study involving 173 pregnant women. The data are observed values of the β human chorionic gonadotropin hormone measured during the first 80 days of gestational age, including from one up to six longitudinal responses for each woman. The main objective in this study is to predict normal versus abnormal pregnancy outcomes from data that are available at the early stages of pregnancy. We achieve the desired classification with a semiparametric hierarchical model. Specifically, we consider a Dirichlet process mixture prior for the distribution of the random effects in each group. The unknown random-effects distributions are allowed to vary across groups but are made dependent by using a design vector to select different features of a single underlying random probability measure. The resulting model is an extension of the dependent Dirichlet process model, with an additional probability model for group classification. The model is shown to perform better than an alternative model which is based on independent Dirichlet processes for the groups. Relevant posterior distributions are summarized by using Markov chain Monte Carlo methods.     

COVARIANCE MODELS FOR LATTICE DATA

Given observations on an m × n lattice, approximate maximum likelihood estimates are derived for a family of models including direct covariance, spatial moving average, conditional autoregressive and simultaneous autoregressive models. The approach involves expressing the (approximate) covariance matrix of the observed variables in terms of a linear combination of neighbour relationship matrices, raised to a power. The structure is such that the eigenvectors of the covariance matrix are independent of the parameters of interest. This result leads to a simple Fisher scoring type algorithm for estimating the parameters. The ideas are illustrated by fitting models to some remotely sensed data.     

Bayesian hierarchical regression models for detecting QTLs in plant experiments

Quantitative trait loci (QTL) mapping is a growing field in statistical genetics. In plants, QTL detection experiments often feature replicates or clones within a specific genetic line. In this work, a Bayesian hierarchical regression model is applied to simulated QTL data and to a dataset from the Arabidopsis thaliana plants for locating the QTL mapping associated with cotyledon opening. A conditional model search strategy based on Bayesian model averaging is utilized to reduce the computational burden.     

Relationship of Dyadic Closeness With Work‐Related Stress: A Daily Diary Study

We examined the association between work‐related stress of both spouses and daily fluctuations in their affective states and dyadic closeness. Daily diary data from 169 Israeli dual‐earner couples were analyzed using multilevel modeling. The findings indicate that work stress has no direct effect on dyadic closeness but rather is mediated by the spouses’ negative mood. Evidence was found for spillover of stress from work to mood at home, as well as negative crossover among couples with higher marital quality, resulting in greater distance on stressful days. Such increased distance may reflect either a deleterious effect of work stress on marital relationships or a protective mechanism used by couples in times of stress.     

Generalizability of Gottman and Colleagues' Affective Process Models of Couples' Relationship Outcomes

The generalizability of Gottman et al's. (1998) affective process models was examined using a community-based sample of 85 married or cohabiting couples with at-risk backgrounds. Predictive associations between affective processes assessed at about age 21 years and relationship status and satisfaction approximately 2.5 years later were examined. The major findings of Gottman et al. failed to replicate. In particular, men's rejection of their partners' influence, the lack of men's deescalation of partners' negative affect, and women's negative start up were not predictive of relationship status. Further, differences in affective processes were found when comparing discussion sessions of the men's versus the women's chosen topics. The findings suggested that the validity and utility of the affective process models need further investigation.     

形式规则还是心理模型--演绎推理过程中两种判断标准的比较研究

演绎推理是人类独有的高级认知活动.然而心理学家对于人们是如何进行推理的一直存在两种不同意见有人认为推理是依赖于形式规则进行的;而另一些人则认为推理是依赖于心理模型的语义过程.对这两种判断标准理论进行分析和研究,心理模型理论在如下三个方面优于形式规则理论一是心理模型理论比形式规则理论适用的范围更广;二是心理模型理论对无效判断更为关注;三是心理模型理论关注系统错误.     

Analysis of growth curve data by using cubic smoothing splines

Longitudinal data frequently arises in various fields of applied sciences where individuals are measured according to some ordered variable, e.g. time. A common approach used to model such data is based on the mixed models for repeated measures. This model provides an eminently flexible approach to modeling of a wide range of mean and covariance structures. However, such models are forced into a rigidly defined class of mathematical formulas which may not be well supported by the data within the whole sequence of observations. A possible non-parametric alternative is a cubic smoothing spline, which is highly flexible and has useful smoothing properties. It can be shown that under normality assumption, the solution of the penalized log-likelihood equation is the cubic smoothing spline, and this solution can be further expressed as a solution of the linear mixed model. It is shown here how cubic smoothing splines can be easily used in the analysis of complete and balanced data. Analysis can be greatly simplified by using the unweighted estimator studied in the paper. It is shown that if the covariance structure of random errors belong to certain class of matrices, the unweighted estimator is the solution to the penalized log-likelihood function. This result is new in smoothing spline context and it is not only confined to growth curve settings. The connection to mixed models is used in developing a rough testing of group profiles. Numerical examples are presented to illustrate the techniques proposed.     

Diesel Engine Exhaust and Lung Cancer Mortality: Time‐Related Factors in Exposure and Risk

To develop a quantitative exposure‐response relationship between concentrations and durations of inhaled diesel engine exhaust (DEE) and increases in lung cancer risks, we examined the role of temporal factors in modifying the estimated effects of exposure to DEE on lung cancer mortality and characterized risk by mine type in the Diesel Exhaust in Miners Study (DEMS) cohort, which followed 12,315 workers through December 1997. We analyzed the data using parametric functions based on concepts of multistage carcinogenesis to directly estimate the hazard functions associated with estimated exposure to a surrogate marker of DEE, respirable elemental carbon (REC). The REC‐associated risk of lung cancer mortality in DEMS is driven by increased risk in only one of four mine types (limestone), with statistically significant heterogeneity by mine type and no significant exposure‐response relationship after removal of the limestone mine workers. Temporal factors, such as duration of exposure, play an important role in determining the risk of lung cancer mortality following exposure to REC, and the relative risk declines after exposure to REC stops. There is evidence of effect modification of risk by attained age. The modifying impact of temporal factors and effect modification by age should be addressed in any quantitative risk assessment (QRA) of DEE. Until there is a better understanding of why the risk appears to be confined to a single mine type, data from DEMS cannot reliably be used for QRA.     

The mobility problem in Britain: new findings from the analysis of birth cohort data

Social mobility is now a matter of greater political concern in Britain than at any time previously. However, the data available for the determination of mobility trends are less adequate today than two or three decades ago. It is widely believed in political and in media circles that social mobility is in decline. But the evidence so far available from sociological research, focused on intergenerational class mobility, is not supportive of this view. We present results based on a newly‐constructed dataset covering four birth cohorts that provides improved data for the study of trends in class mobility and that also allows analyses to move from the twentieth into the twenty‐first century. These results confirm that there has been no decline in mobility, whether considered in absolute or relative terms. In the case of women, there is in fact evidence of mobility increasing. However, the better quality and extended range of our data enable us to identify other ‘mobility problems’ than the supposed decline. Among the members of successive cohorts, the experience of absolute upward mobility is becoming less common and that of absolute downward mobility more common; and class‐linked inequalities in relative chances of mobility and immobility appear wider than previously thought.     

Widowhood and Well‐being in Europe: The Role of National and Regional Context

Researchers have documented that widows have lower levels of subjective well‐being than married individuals, but we still know little about how the regional and national contexts affect the impact of widowhood on well‐being. Building on social capital theory and using data from 5 rounds of the European Social Survey (N= 119,292 people, 206 regions, 23 countries), the authors tested how marital status composition at the national and regional levels affects the well‐being of widows. Widows fare worse in countries with high proportions of married people and in regions and countries with high proportions of widowed persons. The proportion of married individuals at the regional level does not affect their well‐being. These results are in line with the greedy marriage hypothesis, but varying effects at regional and national levels suggest that the standard explanation for this phenomenon, lack of individual social support, is not valid. This study demonstrates the importance of multiple contextual embeddedness.