ISSN:0277-6715    

DOI:10.1002/sim.4780091202

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

年代:1990

数据来源: WILEY

摘要:

AbstractAnalyses of studies of the epidemiology and natural history of infection with the Human Immunodeficiency Virus and subsequent onset of AIDS are complicated by many statistical issues. Several such problems are associated with the nature of data collection which is often incomplete. Here we briefly survey some of the statistical methods that have been developed to meet the needs of analysis of AIDS data. In particular, we consider projection of the number of future cases, and estimation and identification of two key epi‐demiological unknowns, namely the properties of theincubation distributionand those of theinfectivityassociated with transmissio

ISSN:0277-6715    

DOI:10.1002/sim.4780091203

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn clinical trials of long‐term therapies, patients often terminate their treatments earlier than planned. When analysing time‐to‐failure data, one approach to account for early treatment termination censors failure at the time of termination of therapy. In general, however, this does not produce valid inferences about the distribution of time to failure that would have occurred had treatment not been terminated. In contrast, intent‐to‐treat analyses, which are based on time to failure regardless of whether and when treatment is terminated, always produce valid inferences about the unconditional distribution of time to failure. Early treatment termination does not distort the size (type I error rate) of intent‐to‐treat tests but can cause a loss in power. Modifications to ordinary logrank tests can be used to recover some of the lost power without affecting test size, and can be most useful when the proportion of at‐risk patients still taking their treatment changes substantially during periods when failures are observed. Extensions of the modified test to include strata are straightforward, although important design questions require f

ISSN:0277-6715    

DOI:10.1002/sim.4780091204

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

年代:1990

数据来源: WILEY

ISSN:0277-6715    

DOI:10.1002/sim.4780091205

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

年代:1990

数据来源: WILEY

ISSN:0277-6715    

DOI:10.1002/sim.4780091206

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

年代:1990

数据来源: WILEY

摘要:

AbstractPerforming planned or unplanned interim analyses on accumulating data in clinical trials is a frequent practice. In this paper, we propose a general one‐parameter family of type I error probability spending functions to construct customized group sequential boundaries with unequal increments in information time. This proposed family generalizes the spending functions of Lan and DeMets1and Kim and DeMets.2We give an example to illustrate the use of this famil

ISSN:0277-6715    

DOI:10.1002/sim.4780091207

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

年代:1990

数据来源: WILEY

摘要:

AbstractWhen it is required to establish a materially significant difference between two treatments, or, alternatively, to show that two treatments are equivalent, standard test statistics and sample size formulae based on a null hypothesis of no difference no longer apply. This paper reviews some of the test statistics and sample size formulae proposed for comparative binomial trials when the null hypothesis is of a specified non‐zero difference or non‐unity relative risk. Methods based on restricted maximum likelihood estimation are recommended and applied to studies of pertussis vacc

ISSN:0277-6715    

DOI:10.1002/sim.4780091208

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

年代:1990

数据来源: WILEY

摘要:

AbstractResults of a controlled experiment are often adjusted for covariates found by a preliminary test to differ significantly between the treatment and control groups. The resulting test's true significance level is lower than the nominal level. Greater power can be achieved by always adjusting for a covariate that is highly correlated with the response regardless of its distribution between groups.

ISSN:0277-6715    

DOI:10.1002/sim.4780091209

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe linear relationship between the measurements of two methods is estimated on the basis of a weighted errors‐in‐variables regression model that takes into account a proportional relationship between standard deviations of error distributions and true variable levels. Weights are estimated by an iterative procedure. As shown by simulations, the regression procedure yields practically unbiased slope estimates in realistic situations. Standard errors of slope and location difference estimates are derived by the jackknife principle. For illustration, the linear relationship is estimated between the measurements of two albumin methods with proportional err

ISSN:0277-6715    

DOI:10.1002/sim.4780091210

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

年代:1990

数据来源: WILEY

摘要:

AbstractWe investigate the allocation of samples over strata in case‐control studies with consideration of sampling costs. We consider two situations, typical of strata‐matched case‐control studies. Subject to a fixed total cost we derive optimum allocations that maximize the asymptotic efficiency of Cochran's test, that is, minimize the variance of the maximum likelihood estimator of the common odds ratio when the common odds ratio is one. Our results show that the standard design with equal numbers of cases and controls in each stratum is inefficient when costs per control differ greatly from stratum to stratum. We show that the optimum design suggested in this paper is robust for values of the odds ratio common in epidemiologic st

ISSN:0277-6715    

DOI:10.1002/sim.4780091211

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

年代:1990

数据来源: WILEY