摘要:

AbstractThis paper reviews methods for mapping geographical variation in disease incidence and mortality. Recent results in Bayesian hierarchical modelling of relative risk are discussed. Two approaches to relative risk estimation, along with the related computational procedures, are described and compared. The first is an empirical Bayes approach that uses a technique of penalized log‐likelihood maximization; the second approach is fully Bayesian, and uses an innovative stochastic simulation technique called the Gibbs sampler. We chose to map geographical variation in breast cancer and Hodgkin's disease mortality as observed in all the health care districts of Sardinia, to illustrate relevant problems, methods and technique

ISSN:0277-6715    

DOI:10.1002/sim.4780110802

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

年代:1992

数据来源: WILEY

摘要:

AbstractKnowledge of the characteristics of survey non‐respondents is important to determine generalizability to the population of interest. In a recent random‐digit dialling survey of health behaviours only 73 per cent of the households contacted provided any information about household composition, and only 74 per cent of those actually completed the extended interview, for an overall response rate of 54 per cent. To identify possible biases we grouped all attempted phone numbers by their prefix, and looked for the association between the response rate for that prefix and other summary variables known about the prefix. A simulation study showed that the method can identify non‐response biases if certain assumptions are correct. The analysis suggested that our survey data under‐represent older people and those with a college education. We found no significant biases in health behaviours, possibly because the basic assumptions did not hold. This method may assist in identification of non‐response bias in othe

ISSN:0277-6715    

DOI:10.1002/sim.4780110803

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

年代:1992

数据来源: WILEY

摘要:

AbstractDetermination of the equation that relates an ordered dependent variable to ordered independent variables is sought. One solution, non‐parametric discriminant analysis (NPD), involves obtaining the best monotonic step function by means of a computer search procedure. Although one can use alternative selection criteria in obtaining the equation, the illustrative examples use absolute distance. This paper compares the prediction procedures obtained from NPD with those from linear discriminant analysis, linear regression (with and without transformed variables), and logistic regression. We show that NPD is analogous to regression tree analysis with incorporation of ordered variables and monotonicity. We use various prediction functions to predict the example data, the data using the leave‐one‐out technique, and a verification set. Consistently, non‐parametric discriminant analysis performs as good as or better than the tested alter

ISSN:0277-6715    

DOI:10.1002/sim.4780110804

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

年代:1992

数据来源: WILEY

摘要:

AbstractVarious techniques are available for the analysis of repeated measures data, and the appropriate choice depends on distributional assumptions and study design features. A correct analysis must account for potential dependence between repeated observations on the same subject. Liang and Zeger proposed a more unified approach to the analysis of repeated measures data based on the application of generalized estimating equations. We examine the application of these methods to several types of data in which one estimates the mean response directly for each combination of discrete covariates, and uses an identity link. Computations for fitting this type of model are exceptionally simple. Numerical examples suggest that the proposed approach yields estimation and hypothesis testing results consistent with more specialized methods.

ISSN:0277-6715    

DOI:10.1002/sim.4780110805

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

年代:1992

数据来源: WILEY

摘要:

AbstractUltrasonographic measurement of intima‐media thicknesses in the carotid artery has emerged as an important non‐invasive means of assessing atherosclerosis, and has served to define primary outcome measures related to progression of arterial lesions in several large clinical trials and epidemiologic studies. It is characteristic that measurements often cannot be obtained from all sites during repeated examinations. This leads to incomplete multivariate serial data, for which the set and number of visualized sites may vary across time. We have contrasted several conditional and unconditional maximum likelihood analytical approaches, and have evaluated these with a simulation experiment based on characteristics of ultrasound measurements collected during the course of the Asymptomatic Carotid Artery Plaque Study. We examined analyses based on unweighted and generalized least squares regression in which we estimated cross‐sectional summary statistics using raw means, unconditional maximum likelihood estimates and full maximum likelihood estimates. Since the genesis of missing data is not fully clear, and since the approaches we examined are based, to some degree, on the assumption that data are missing at random, we also examined the relative impact of deviations from such an assumption on each of the approaches considered. We found that maximum likelihood based approaches increased the expected efficiency of the analysis of serial ultrasound data over ignoring missing data by up to 21 per

ISSN:0277-6715    

DOI:10.1002/sim.4780110806

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

年代:1992

数据来源: WILEY

摘要:

AbstractD'Agostino and Heeren (DH) discussed the multiple comparison issues that arise in evaluating both sensitivity and efficacy in over‐the‐counter drug trials. We propose a general definition of sensitivity that includes DH's definition as a special case. We also propose a test for sensitivity that coincides with the MIN test of Laska and Meisner at one extreme but has the advantage of identifying specific drugs satisfying the sensitivity criterion when some fail to do so. We suggest that the test of Dunnett as well as an extension of it may be useful for the efficacy comparis

ISSN:0277-6715    

DOI:10.1002/sim.4780110807

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

年代:1992

数据来源: WILEY

摘要:

AbstractMany pharmaceutical companies are now exploring combination drug therapies as an alternative to monotherapy. Consequently, it is of interest to investigate the simultaneous dose response relationship of two active drugs to select the lowest effective combination. In this paper, we propose a method for designing clinical trials for drug combinations that seems to offer several advantages over the 4 × 3 or even larger factorial studies that have been used to date. In addition, our proposed method provides a convenient formula for calculating the required sample size

ISSN:0277-6715    

DOI:10.1002/sim.4780110808

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe collection of safety data is an important part of clinical trials. These safety data are often described and reported in great detail with expenditure of substantial effort and energy. Because of the wide variety of data that require scrutiny from the safety perspective, however, statistical comparisons of the safety profiles of different treatments often lack focus and structure and result in situations where the comparisons for each individual item lack power and thus are inconclusive. In this paper, we propose to organize the safety data into a more manageable form by consolidating them into a number ofKclasses characterized by body systems and determined in conjunction with the underlying disease as well as the treatments involved. Within each class, we propose assignment to each patient of an overall intensity grade based on all relevant information. The consolidation of the safety data as proposed provides an informative summary for the safety profile of each treatment. The analysis of such organized data concentrates on comparison of the mean intensity grades for different treatments within theKclasses simultaneously with use of scores that reflect the acceptability of the various intensity levels to an individual. Furthermore, we demonstrate that the proposed multivariate comparison has much higher power than the univariate one to detect differences in certain cases. We provide examples to illustrate the proposed procedure.

ISSN:0277-6715    

DOI:10.1002/sim.4780110809

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

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper compares the sample size formulae given by Schoenfeld, Freedman, Hsieh and Shuster for unbalanced designs. Freedman's formula predicts the highest power for the logrank test when the sample size ratio of the two groups equals the reciprocal of the hazard ratio. The other three formulae predict highest powers when sample sizes in the two groups are equal. Results of Monte Carlo simulations performed for the power of the logrank test with various sample size ratios show that the power curve of the logrank test is almost flat between a sample size ratio of one and a sample size ratio close to the reciprocal of the hazard ratio. An equal sample‐size allocation may not maximize the power of the logrank test. Monte Carlo simulations also show that, under an exponential model, when the sample size ratio is toward the reciprocal of the hazard ratio, Freedman's formula predicts more accurate powers. Schoenfeld's formula, however, seems best for predicting powers with equal sample siz

ISSN:0277-6715    

DOI:10.1002/sim.4780110810

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

年代:1992

数据来源: WILEY

摘要:

AbstractI suggest for memorization an equation for calculating approximate sample size requirements intended only for a specific set of values (80 per cent power for a two‐tailed alpha = 0.05 test) which seems to occur often in biopharmaceutical research. After presenting the formula in terms of variance estimates2and effect sized, I derive a few alternative forms and then discuss the accuracy of the approximation and other properties as well as examples of its us

ISSN:0277-6715    

DOI:10.1002/sim.4780110811

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

年代:1992

数据来源: WILEY