Suchergebnisse

The standard latent class model is a finite mixture of indirectly observed multinomial distributions, each of which is assumed to exhibit statistical independence. Latent class analysis has been applied in a wide variety of research contexts, including studies of mobility, educational attainment, agreement, and diagnostic accuracy, and as measurement error models in social research. One of the attractive features of the latent class model in these settings is that the parameters defining the individual multinomials are readily interpretable marginal probabilities, conditional on the unobserved latent variable(s), that are often of substantive interest. There are, however, settings where the local-independence axiom is not supported, and hence it is useful to consider some form of local dependence. In this paper we consider a family of models defined in terms of finite mixtures of multinomial models where the multinomials are parameterized in terms of a set of models for the univariate marginal distributions and for marginal associations. Local dependence is introduced through the models for marginal associations, and the standard latent class model obtains as a special case. Three examples are analyzed with the models to illustrate their utility in analyzing complex cross-classifications.

An approximate relationship between the odds ratio and the tetrachoric correlation for 2×2 contingency tables is presented. The approximation is simple in form and demonstrates a close linkage between these two important measures of association. This relationship can be used to reconcile (at least in part) the two ostensibly different ways to study association or partial association. The approximation is related to Yule's Q and can also be motivated by recent results on association models. The approximation is used to relate the parameters of the common factor model and the 2-class latent structure model applied to dichotomous items.

Log-linear models are useful for analyzing cross-classifications of counts arising in sociology, but it has been argued that in some cases, an alternative approach for formulating models—one based on simultaneously modeling univariate marginal logits and marginal associations—can lead to models that are more directly relevant for addressing the kinds of questions arising in those cases. In this article, the authors explore some of the similarities and differences between the log-linear models approach to modeling categorical data and a marginal modeling appraoch. It has been noted in past literature that the model of statistical independence is conveniently represented within both approaches to specifying models for cross-classifications of counts. The authors examine further the extent to which the two families of models overlap, as well as some important differences. The authors do not present a complete characterization of the conditions describing the intersection of the two families of models but cover many of the models for bivariate contingency tables and for three-way contingency tables that are routinely used in sociological research.

Die additive Fertigung von Kunststoffbauteilen mit dem selektiven Lasersintern (SLS) hat sich für diverse Anwendungen etabliert und bietet durch die großen geometrischen Freiheiten vielfältige Anwendungsmöglichkeiten. Weitere Anwendungen wären zu erschließen, wenn diskrete Bauteile vollständig integriert werden könnten, sodass hybride Bauteile entstehen. Daher wurde am Fraunhofer IPA untersucht, ob und wie der SLS-Prozess unterbrochen und Komponenten vollständig umdruckt werden können.
 
The additive manufacturing of plastic components by means of selective laser sintering (SLS) is established for various applications , offers a broad range of possible applications due to the wide geometrical freedom. Further applications could be tapped into with discrete components being fully integrated, resulting in hybrid components. This is why Fraunhofer IPA investigated if and how the SLS process can be interrupted and components be completely reprinted.

This study examines the association between scope of Quality Improvement (QI) implementation in hospitals and hospital performance on patient safety indicators. Secondary data sources included a 1997 survey of hospital QI practices, Medicare Inpatient Database, American Hospital Association's Annual Survey of Hospitals, the Bureau of Health Professions'Area Resource File, and two proprietary data sets. Using a sample of 1,784 community hospitals, the study employed two-stage instrumental variables estimation in which predicted values of four QI scope variables and control variables were used to estimate four patient safety indicators. Involvement by multiple hospital units in the QI effort is associated with worse values on all four patient safety indicators. Percentages of hospital staff and of senior managers participating in QI teams exhibited no statistically significant association with any patient safety indicator. Percentage of physicians participating in QI teams is associated with better values on two patient safety indicators.

We examined the utility of a newly developed perceived air pollution (PAP) scale and of a modeled air pollution (MAP) scale derived from it for predicting previously observed birth outcomes of pregnant women enrolled following September 11, 2001. Women reported their home and work locations in the four weeks after September 11, 2001 and the PAP at each site on a four‐point scale designed for this purpose. Locations were geocoded and their distance from the World Trade Center (WTC) site determined. PAP values were used to develop a model of air pollution for a 20‐mile radius from the WTC site. MAP values were assigned to each geocoded location. We examined the relationship of PAP and MAP values to maternal characteristics and to distance of home and work sites from the WTC site. Both PAP and MAP values were highly correlated with distance from the WTC. Maternal characteristics that were associated with PAP values reported for home or work sites (race, demoralization, material hardship, first trimester on September 11) were not associated with modeled MAP values. Relationships of several birth outcomes to proximity to the WTC, which we previously reported using this data set, were also seen when MAP values were used as the measure of exposure, instead of proximity. MAP developed from reports of PAP may be useful to identify high‐risk areas and predict health outcomes when there are multiple sources of pollution and a "distance from source" analysis is impossible.