摘要:

AbstractIn this paper, we examine three approaches for comparing several treatments with a control with use of binary response data. The first approach relies on asymptotic theory applied to the Freeman—Tukey transformation of the observed proportions. The second finds an acceptance region based on the binomial distributions estimated under the joint null hypotheses. The third approach applies Dunnett's procedure to the binary data. We evaluated the actual overall type I error rates of the Freeman—Tukey test and Dunnett's procedure using both simulation and binomial calculations while we assessed those of the binomial approach using simulation. Based on their capability to preserve the desirable overall type I error rate, we provide recommendations regarding the choices among the three approaches for various occasions. In addition, we provide comments on the power of these three procedu

ISSN:0277-6715    

DOI:10.1002/sim.4780142302

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

年代:1995

数据来源: WILEY

摘要:

AbstractI present an analysis of data from a clinical trial of new chemotherapies for colorectal cancer. I model participating clinical sites via random effects, to allow for heterogeneous patient responses across centres. Patient response is measured by both progression and survival times. The data suggest that patient responses are homogeneous before, but heterogeneous after, disease progression. For one new therapy, an increase in efficacy relative to standard therapy is detected before, but not after, progression.

ISSN:0277-6715    

DOI:10.1002/sim.4780142303

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

年代:1995

数据来源: WILEY

摘要:

AbstractBrookmeyer and Crowley derived a non‐parametric confidence interval for the median survival time of a homogeneous population by inverting a generalization of the sign test for censored data. The 1 – α confidence interval for the median is essentially the set of all valuestsuch that the Kaplan—Meier estimate of the survival curve at timetdoes not differ significantly from one‐half at the two‐sided α level. Su and Wei extended this approach to the two‐sample problem and derived a confidence interval for the difference in median survival times based on the Kaplan‐Meier estimates of the individual survival curves and a ‘minimum dispersion’ test statistic. Here, I incorporate covariates into the analysis by assuming a proportional hazards model for the covariate effects, while leaving the two underlying survival curves virtually unconstrained. I generate a simultaneous confidence region for the two median survival times, adjusted to any selected value,z, of the covariate vector using a test‐based approach analogous to Brookmeyer and Crowley's for the one‐sample case. This region is, in turn, used to derive a confidence interval for the difference in median survival times between the two treatment groups at the selected value ofz. Employment of a procedure suggested by Aitchison sets the level of the simultaneous region to a value that should yield, at least approximately, the desired confidence coefficient for the difference in medians. Simulation studies indicate that the method provides reasonably accurate

ISSN:0277-6715    

DOI:10.1002/sim.4780142304

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

年代:1995

数据来源: WILEY

摘要:

AbstractThis paper establishes the asymptotic properties of the non‐parametric maximum likelihood estimator of the survival function based on data censored both from the left and the right. We show that the sample mean based on the survival estimator converges to a normal distribution, and we derive non‐parametric tests for the differences in survival functions. The methods are applied to a study of dementia associated with Parkinson's dise

ISSN:0277-6715    

DOI:10.1002/sim.4780142305

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

年代:1995

数据来源: WILEY

摘要:

AbstractEvaluative composite measurement scales (CMS) are increasingly used in medicine to measure complex constructs in the absence of a reference criterion or ‘gold standard’. However, the level of measurement provided by these instruments has usually been given little attention. This paper explores the influence of the characteristics of the item set and weighting on the level of measurment of an evaluative CMS. The approach is illustrated with an application to the scoring system of the Nottingham Health Profile. Simulations are provided to indicate when the composite score of item responses, on an ordinal or pass—fail scale, could be considered to achieve the properties of an interval

ISSN:0277-6715    

DOI:10.1002/sim.4780142306

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

年代:1995

数据来源: WILEY

摘要:

AbstractWe consider the design of both cohort and case‐control studies in which an initial (‘stage 1’) sample of complete data on an error‐free disease indicator(D), a correct (‘gold‐standard’) dichotomous exposure measurement(X)and an error‐prone exposure measurement(Z)are available. We calculate the amount of additional information on the odds ratio relatingDtoXthat one can obtain from a second (‘stage 2’) sample of measurements only onDandZ. If one allows for differential measurement error inZ, there is often little advantage in having more than four times as much data in stage 2 data as in stage 1. With the assumption that a non‐differential measurement error model is reasonable, larger amounts of stage 2 data can be useful. Simulations indicate that stage 1 samples of modest size (50 cases in case‐control studies and 50 failures in cohort studies) yield sufficiently reliable estimates of needed parameters to assist in determining an appropriate size for the stage 2 sample. These ideas apply in settings either where the amount of stage 1 data is limited and fixed by external constraints or where one has gathered stage 1 data in advance to avoid collecting s

ISSN:0277-6715    

DOI:10.1002/sim.4780142307

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

年代:1995

数据来源: WILEY

摘要:

AbstractDiabetes mellitus is a common condition which has several serious complications associated with it. In this paper a mixture model, based on one previously used to predict the onset of AIDS, is used to predict the onset of one of these complications, diabetic retinopathy, the major cause of adult blindness in the U.K. This model differs from the previous AIDS model by introducing covariates into the model and using a wider choice of mixture distributions. The fit and distributional assumptions of the model are then discussed for this example. The model is fitted to the data by maximum likelihood. It is important that the training set contains balanced numbers of individuals with and without retinopathy.

ISSN:0277-6715    

DOI:10.1002/sim.4780142308

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe shape of the plaque pH‐profile after consumption of a food item determines the food's potential caries risk. This and related facts have caused an increased interest in measurements of plaque pH‐profiles during the last decade. A standard design for these measurements is to take equally spaced observations over a certain period of time. The theory of optimal experimental design gives methods for positioning the measurements of a pH‐profile in an optimized way. The objective is to minimize the effort given a desired precision of the estimated profile characteristics or to maximize the precision given the number of measurements. We show that a reduction in the number of measurements up to 50 per cent or a respective improvement in precision of the estimates as compared to standardly applied designs is possible. This implies less inconvenience for the subjects and better compliance with the needs of investigation. Our study is intended to demonstrate the applicability of the theory of optimal experimental design which has the potential to improve the efficiency of medical res

ISSN:0277-6715    

DOI:10.1002/sim.4780142309

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

年代:1995

数据来源: WILEY

ISSN:0277-6715    

DOI:10.1002/sim.4780142310

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

年代:1995

数据来源: WILEY

ISSN:0277-6715    

DOI:10.1002/sim.4780142311

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

年代:1995

数据来源: WILEY