ISSN:0277-6715    

DOI:10.1002/sim.4780120312

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractSurvival analysis methods are valuable for detecting intervention effects because detailed information from patient records and sensitive outcome measures are used. The burn unit at a large university hospital replaced routine bathing with total body bathing using chlorhexidine gluconate for antimicrobial effect. A Cox proportional hazards model was used to analyse time from admission until either infection withStaphylococcus aureusor discharge for 155 patients, controlling for burn severity and two time‐dependent covariates: days until first wound excision and days until first administration of prophylactic antibiotics. The risk of infection was 55 per cent higher in the historical control group, although not statistically significant. There was also some indication that early wound excision may be important as an infection‐control measure for burn patie

ISSN:0277-6715    

DOI:10.1002/sim.4780120313

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAIDS incidence trends vary greatly among geographic areas in the United States. We define clusters of areas within which AIDS incidence trends are similar, as areas within a cluster may have similar human immunodeficiency virus epidemic patterns and thus may lead to similar prevention/intervention strategies. Methods of exploratory data analysis are used to define such clusters from reported quarterly AIDS incidence to December 1990 (adjusted for estimated reporting delays) in homosexual and bisexual men not using intravenous drugs in 39 metropolitan statistical areas (MSAs) in the United States. After smoothing AIDS incidence in each MSA, we define groups from cluster analysis based on a measure of similarity between pairs of MSAs. A log‐linear model gives estimates of the scale factors and the common trend for the MSAs in each group. Alternative metrics and simulated data suggest that the clustering is fairly robust to variations in AIDS incidence data. The resulting clusters separate MSAs with different trends, for example, MSAs in which AIDS incidence shows signs of reaching a plateau are separated from MSAs in which incidence continues to increase rapidl

ISSN:0277-6715    

DOI:10.1002/sim.4780120314

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractCurrently, there is considerable interest in studies that use the community as the experimental unit. Health promotion programmes are one example. Because such activities are expensive, the number of experimental units (communities) is usually very small. Investigators often match communities on demographic variables in order to improve the power of their studies. Matching is known to improve power in certain circumstances. However, we show here that if the number of communities is small, the matched design will probably have less power than the unmatched design. This is due primarily to the loss of degrees of freedom in the matched design, which outweighs the benefits of matching on any but the strongest correlates of changes in behaviour. In the community intervention situation, even small differences in sample size between the matched and unmatched analyses can have expensive consequences.

ISSN:0277-6715    

DOI:10.1002/sim.4780120315

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractDecisions regarding the design and analysis of a phase III study to reduce the incidence of colorectal polyps must take into account two complicating factors: the possibility that polyps are missed during screening exams, and variable lengths of follow‐up. In this paper we investigate the effects due to misclassification on the power of statistical tests to detect a change in polyp recurrence rates. We also use Monte Carlo studies to examine the relative efficiency of different methods of adjusting for variable times of follow

ISSN:0277-6715    

DOI:10.1002/sim.4780120316

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWe examined selected issues in data analysis in the Collaborative Review of Sterilization (CREST). CREST is a multicentre, prospective, observational study of women undergoing tubal sterilization. We analysed menstrual function after sterilization in over 5000 women who were enrolled in the period 1978–1983 and followed for 5 years with yearly follow‐up interviews. To take into account the dependency among repeated responses from the same individuals, we used the generalized estimating equations (GEE) approach to longitudinal data analysis. Marginal modelling resulted in a statistically significant increase in the odds of menstrual dysfunction at 5 years after tubal sterilization. Transitional modelling produced rates of menstrual dysfunction given a woman's menstrual function at baseline, after adjusting for other baseline characteristics such as method of contraception before sterilization. To examine the direction of the bias that could result from non‐random missing data, we refitted our models using imputed values. The models with imputed values showed the same trends as the original m

ISSN:0277-6715    

DOI:10.1002/sim.4780120317

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractConversational and refusal assertion skills of 768 seventh grade youth were assessed through ratings of global (for example, effectiveness) and non‐verbal (for example, eye contact) behaviour performed in two role‐play scenarios. The ratings were completed after each scenario by the subjects themselves, as well as by classmate and trained adult observers. Use of the Hays and Hayashi multitrait scaling method to interpret these data revealed two results. First, the items used to measure role‐play behaviour did not achieve sufficient internal consistency to create global and non‐verbal composites. Second, inter‐rater agreement and discriminant validity were obtained only for ratings of the global effectiveness of each of the two social skills. Next, a series of multiple regression analyses indicated that an index of the global effectiveness of refusal assertion skill, but not of conversational skill, was predictive of intention to use tobacco. Those who were relatively unskilful at refusing offers were more likely to intend to use tobacco. Analyses exploring relations of trained observer ratings of the effectiveness of both role‐play types, trained observer ratings of the other global and non‐verbal items, and subjects' intention to use tobacco indicated that only a hesitant voice pattern was both negatively predictive of effective refusal assertion and positively predictive of intention to use tobacco in the future. In other words, those who are hesitant when they refuse a tobacco offer are the ones most likely to report an intention to use tobacco in the future. The consistency of this last finding in the tobacco use prevention literature

ISSN:0277-6715    

DOI:10.1002/sim.4780120318

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractSince birth‐weight‐specific infant mortality rates are widely considered to be measures of the effects of perinatal medical care, birth‐weight‐adjusted and birth‐weight‐specific infant mortality rates have often been used in comparisons across hospitals and geographic areas. Wilcox and Russell1have provided a model which leads to the conclusion that birth weight adjustment is biased against populations with heavier birth weights and that birth‐weight‐specific infant mortality rates can yield misleading results. Nevertheless, evaluators and health planners still need a summary measure of the infant mortality rate in which some sort of birth weight adjustment is used to generate an (appropriately) weighted mean of birth‐weight‐specific relative risks. We used the 1983–85 national linked files of live births and infant deaths to investigate two new methods that extend the Wilcox—Russell approach, ‘mean adjustment’ and ‘Z‐adjustment’, to compare birth‐weight‐specific infant mortality rates among the white populations of the states. Colorado was used as the reference population in logistic regression analyses. Statistical interactions between state and birth weight on the conventional kilogram scale, the mean‐adjusted scale, and the Z scale were examined. There were substantial interactions with birth weight on all three scales. In addition, when Colorado was used as the reference population, mean adjustment shifted the odds ratios downward to implausibly low values, especially at lower weights. The Z‐adjustment method incorporating the Wilcox—Russell approach appears to be a useful alternative to birth weight adjustment. However, because birth‐weight‐specific mortality rates do not differ uniformly across all birth weig

ISSN:0277-6715    

DOI:10.1002/sim.4780120319

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe identification of counties burdened by exceptionally high rates of mortality is a fundamental step in the development of state‐based intervention and prevention strategies. However, the estimation of rates from small geographic areas presents special problems, especially for rare events. This paper compares the use of crude and age‐standardized rates to the use of Poisson regression models and empirical Bayes models for analysing county‐level mortality rates. The results demonstrate both practical and heuristic advantages of the empirical Bayes models. Age‐standardized rates adjust for differences in age structure among counties but are vulnerable to extreme variability in county age‐specific rates. In our example — an analysis of diabetes mortality rates — Poisson regression did not improve the variability of estimated county‐level rates. Adjusted empirical Bayes estimates dramatically shrink the observed rates while preserving some separation of the counties with extreme rates. Also, empirical Bayes estimates of rates for counties with no observed deaths are shrunk close to

ISSN:0277-6715    

DOI:10.1002/sim.4780120320

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractLongitudinally based height velocity centiles for U.S. children, appropriate for paediatric clinical use, were derived for growth from ages 7 to 18 years. A series of gender‐ and race‐specific figures present the median velocity curves for children by year of maturation. Smooth 3rd to 97th centile curves, for blacks and whites together, are provided for children who are early, average, and late maturers. The data were taken from 6532 black and white children participating in the Six Cities Study from 1974 to 1

ISSN:0277-6715    

DOI:10.1002/sim.4780120321

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY