摘要:

AbstractA great need persists for diagnostic criteria for both brain death in young children and irreversible loss of consciousness at all ages. This article examines the inferences derived from a hypothetical confirmatory study in which all of theNpatients who fulfilled the criterion did in fact experience brain death (irreversibility). A Bayesian methodology proves that, forNin the range of a large clinical study, estimations of prior probabilities are, for all practical purposes, irrelevant to the calculation of the posterior probabilities. The risk of a false positive diagnosis for the next patient who meets the criterion is approximately 1/(N+ 2). The chance of at least one false positive diagnosis among the next (N+ 1) patients who meet the criterion is around 50 per cent. Thus, achievement of the requisite moral certainty of a declaration of death (irreversibility) necessitates an impossibly largeNfor the study. This does not mean that one cannot diagnose death, but rather that the validity of the diagnostic criteria must be self‐evident ona priorigrounds, and that confirmatory studies are necessarily either inadequate or superfluou

ISSN:0277-6715    

DOI:10.1002/sim.4780060503

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

年代:1987

数据来源: WILEY

摘要:

AbstractA new method of analysing binary data from a three‐treatment, three‐period cross‐over trial is described. This method is based on a log‐linear model and mirrors the analysis of continuous data. It is an extension of the method we introduced recently for the analysis of binary data from a two‐treatment, two‐period crossover trial. We illustrate our method using data from a trial which compared two analgesics and a placebo for the relief of primary d

ISSN:0277-6715    

DOI:10.1002/sim.4780060504

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe Mantel–Haenszel test provides a straightforward method to combine results from several clinical trials when only summary information, such as the proportion of deaths, is available for each trial. More efficient tests, such as the stratified logrank test, should be used if the survival and censoring times are known for all individuals, but in practice, the cost and effort of obtaining this information may be prohibitive. The purpose of this paper is to derive a general expression for the asymptotic relative efficiency (ARE) of the Mantel–Haenszel test with respect to the stratified logrank test, and to compute the ARE in situations which are likely to be of practical interest. The results show that under realistic assumptions about the survival distribution, losses to follow‐up and duration of accrual, the ARE frequently exceeds 80 per cent. An example is given to show the usefulness of the approach when combining proportions of deaths from several cancer clinical t

ISSN:0277-6715    

DOI:10.1002/sim.4780060505

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

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper presents a simple method of calculating sample sizes for unequal‐sample‐size designs with use of published tables applicable to equal‐sample‐size designs. The method applies to both the logrank test and thet‐test. For the power of logrank test, this paper compares the proposed method with existing methods and with the Monte Carlo s

ISSN:0277-6715    

DOI:10.1002/sim.4780060506

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

年代:1987

数据来源: WILEY

摘要:

AbstractFor analysis of data from a titration study, this paper adopts the idea of a life table analysis and utilizes a logistic linear dose–response model. The procedure uses iterated reweighted least‐squares to provide parameter estimates. Computation of the asymptotic covariance of the life‐table estimates of the response rates involves Greenwood's formula and a conditioning argument. A special case consists of examination of the covariance structure when no dropouts took place. Data from a titration study that investigated the efficacy of an anti‐hypertensive compound illustrate the pr

ISSN:0277-6715    

DOI:10.1002/sim.4780060507

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

年代:1987

数据来源: WILEY

摘要:

AbstractWe propose ak‐ratio method for multiple comparisons among disjoint groups in survival analysis, specifically among relative risk estimates from a proportional hazards regression analysis. The new method relates the magnitude of critical values to an overall measure of group heterogeneity. That is, large critical values result from small values of a chi‐square statistic for testing between‐groups homogeneity. Conversely, large values of the overall statistic lead to small critical values for individual comparisons, even if there are many groups. The adaptivity of thek‐ratio method contrasts sharply with the conservatism of competing

ISSN:0277-6715    

DOI:10.1002/sim.4780060508

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

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper discusses and compares several estimators of mean rate of change in unbalanced longitudinal data based on a model with randomly distributed regression coefficients across individuals. The estimators are unweighted and weighted means of these coefficients. The paper also evaluates commonly used variance estimates corresponding to the estimators. Results show that in situations of very slight imbalance, the choice of method is not critical. When imbalance is substantial, however, one should weight the regression coefficients by their estimated precision. An example using data from a nutritional study on premature neonates illustrates some issues encountered in the analysis of longitudinal clinical data sets.

ISSN:0277-6715    

DOI:10.1002/sim.4780060509

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe validity of information obtained from women about the medical aspects of their childbearing experiences has been assessed by comparing the responses of 223 mothers on a postal questionnaire with information extracted from their medical records. When discrepancies between the two sources were found, it was not assumed that the hospital records were correct. Instead, attempts were made to ascertain why the data might be inconsistent by re‐checking the records and by contacting the mothers again. There appeared to be five main reasons for discrepancies: mothers' limited knowledge or understanding of certain procedures; problems of interpretation and definition; occasionally inaccurate or missing information in the medical records; underreporting of sensitive information by mothers and, finally, questions which were misunderstood or misinterpreted by the mothers. For most items, however, good agreement between the mothers and hospitals was obtained, and the results indicate that valid information over a range of events can be obtained using postal surveys of mother

ISSN:0277-6715    

DOI:10.1002/sim.4780060510

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

年代:1987

数据来源: WILEY

摘要:

AbstractBy choice or necessity, human geneticists and genetic epidemiologists often design studies that involve non‐random sampling of clusters of individuals, and yet address hypotheses appropriate to the population as a whole. Failure to adjust for the non‐randomness of data often leads to biased parameter estimates and misspecification of predictive models that cause familial resemblance of traits. We develop an approach to adjust for common forms of non‐randomness in the context of estimating familial correlation with minimal distributional assumptions and discuss its implications in connection with adjustments for concomitant vari

ISSN:0277-6715    

DOI:10.1002/sim.4780060511

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

年代:1987

数据来源: WILEY

ISSN:0277-6715    

DOI:10.1002/sim.4780060502

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

年代:1987

数据来源: WILEY