摘要:

AbstractThis paper develops and implements a fully Bayesian approach to meta‐analysis, in which uncertainty about effects in distinct but comparable studies is represented by an exchangeable prior distribution. Specifically, hierarchical normal models are used, along with a parametrization that allows a unified approach to deal easily with both clinical trial and case‐control study data. Monte Carlo methods are used to obtain posterior distributions for parameters of interest, integrating out the unknown parameters of the exchangeable prior or ‘random effects’ distribution. The approach is illustrated with two examples, the first involving a data set on the effect of beta‐blockers after myocardial infarction, and the second based on a classic data set comprising 14 case‐control studies on the effects of smoking on lung cancer. In both examples, rather different conclusions from those previously published are obtained. In particular, it is claimed that widely used methods for meta‐analysis, which involve complete pooling of ‘O‐E’ values, lead to understatement of uncertainty in the estimation of overall or

ISSN:0277-6715    

DOI:10.1002/sim.4780110202

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

年代:1992

数据来源: WILEY

摘要:

AbstractIn this note we study, by simulation, small sample performance in terms of size of ten procedures for testing the homogeneity of odds ratios inK2 × 2 contingency tables. These ten statistics are derived for ‘largestratum’ settings. Our study concerns the behaviour of these statistics for ‘small‐stratum

ISSN:0277-6715    

DOI:10.1002/sim.4780110203

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

年代:1992

数据来源: WILEY

摘要:

AbstractWe discuss the implementation of a criterion due to Prentice for the statistical validation of intermediate endpoints for chronic disease. The criterion involves examining in a cohort or intervention study whether an exposure or intervention effect, adjusted for the intermediate endpoint, is reduced to zero. For example, to examine whether serum cholesterol level is an intermediate endpoint for coronary heart disease (CHD), we may investigate the effect of the cholesterol lowering drug cholestyramine on CHD incidence adjusted for serum cholesterol levels. We show that use of this criterion will usually demand some form of model selection. When the unadjusted exposure or treatment effect is less than four times its standard error, the analysis can usually lead only to a weak form of validation, a conclusion that the data are not inconsistent with the validation criterion. More significant unadjusted exposure effects offer the potential for stronger types of validation statement such as ‘the intermediate endpoint explains at least 50 per cent (or 75 per cent) of the exposure effect

ISSN:0277-6715    

DOI:10.1002/sim.4780110204

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

年代:1992

数据来源: WILEY

摘要:

AbstractSeveral methods are available for sample size calculation for clinical trials when survival curves are to be compared using the logrank statistic. We discuss advantages and disadvantages of some of these methods, and present simulation results under exponential, proportional hazards and non‐proportional hazard situation

ISSN:0277-6715    

DOI:10.1002/sim.4780110205

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

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper reviews several tests for censored paired data and uses Monte Carlo methods to evaluate their sizes and powers. Each of the tests maintains its size. The Akritas test and the paired Prentice–Wilcoxon test are somewhat more powerful than the Gehan statistic or the generalized signed rank test for most of the distributions studied. If the survival times follow an exponential distribution, then the Gehan and the generalized signed rank tests are more powerful against a location shift alternativ

ISSN:0277-6715    

DOI:10.1002/sim.4780110206

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe use of multiple reading procedures to improve the performance of a diagnostic test occurs often in practice. Evaluation of the utility of multiple reading procedures, however, usually ignores the effect of the intraclass correlation. This paper provides a quantitative assessment of this effect in the multiple reading procedure with a unanimity rule with respect to sensitivity, specificity, positive and negative predictive values. We have found that when the disease prevalence is rare or moderate (≤ 0·20), use of the multiple reading procedure with a unanimity rule is effective in increasing the positive predictive value of a single reading procedure for the situation in which the variation of responses among different subjects and the intraclass correaltion among repeated tests are small. This is, however, not true for the situation in which the disease is rare and the variation of responses among different subjects is large, even when the intraclass correlation is small or 0. Furthermore, when the disease is rare and the variation of responses among subjects is small, a small or moderate intraclass correlation can substantially decrease the positive predictive value that one calculates under the assumption that the intraclass correlation is equal to 0. In general, when the disease is rare or moderate (≤ 0.20), the intraclass correlation between repeated tests and the variation of responses among subjects have little effect on the negative predictive v

ISSN:0277-6715    

DOI:10.1002/sim.4780110207

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

年代:1992

数据来源: WILEY

摘要:

AbstractThomaset al.1presented the application of empirical‐Bayes methods to the problem of multiple inference in epidemiologic studies. One limitation of their approach, which they noted, was the need to assume exchangeable log relative‐risk parameters, and independent relative‐risk estimates. Numerical integration was also required. Here I generalize their approach to allow for non‐exchangeable parameters and non‐independent estimates. The resulting method is Bayesian in so far as some feature of the prior distribution are specified from prior information, but is empirical Bayes in so far as some explicit parameters in the prior distribution are estimated from the data. Estimation is based on approximations to the posterior distribution; this allows one to implement the approach with standard software packages for matrix algebra. The method is illustrated in an occupational mortality study of 84 exposure‐cancer a

ISSN:0277-6715    

DOI:10.1002/sim.4780110208

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

年代:1992

数据来源: WILEY

摘要:

AbstractThis paper presents a study of the stochastic behaviour of the entry of a 5‐dimensional, 2400 state, system into new states. Each state consists of five measurements on variables that are sensitive measures of the degree of activated unconscious communication. The data come from six psychotherapy consultation sessions. The study sought to investigate the manner in which patient and therapist progress into new configurations (new states) of the five variables, and the way tension accumulates to the point of overcoming the inertia in the patient/therapist system. We show that the time series that consists of the time intervals between successive new states is a generalized Poisson process. That is, the process is inherently governed by a Poisson parameter that is a continuous piecewise linear function of time. It increases rapidly in the opening moments of an interview and decreases slowly thereafter. This non‐linear, non‐stationary Markov model fits the data well according to the Kolmogorov–Smirnoff criterion. We discuss the model's implications for the nature of psychotherapy and its parti

ISSN:0277-6715    

DOI:10.1002/sim.4780110209

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

年代:1992

数据来源: WILEY

摘要:

AbstractIn many medical studies, longitudinal data are collected on each of a sample of patients. The objectives of such studies often are: to estimate and test bivariate or multivariate relationships within each of several groups of patients from these repeated measures data; to compare these relationships among groups; and to test for the effects of baseline covariates on the relationships. This paper illustrates the use of statistical methods for growth curve analysis recently proposed by Vonesh and Carter for achieving these goals by relating a measure of preschool cognitive development to age in four race by sex groups of low‐birth‐weight infants. Significant declines in Bayley's Mental Development Index (MDI) with increasing age were found in all groups. Birth‐weight did not significantly influence the rate of decline but did influence the overall level of performance. Even so, in the group most comparable to Bayley's normative population, predicted MDI was near the norm even for extremely low‐birth‐weight infants (that is, 1000 grams). Although there is some risk of mental deficit associated with prematurity, eventual developmental delays in low‐birth‐weight infants frequently are acquired with age. The rate of decline in MDI was significantly associated with race and mother's education. Assumptions required for the valid application of these methods are discussed and tested in the setting of this applied problem. The assumptions appeared valid in this application. We conclude with a brief discussion of available alternatives when the assumptions are violated and point to areas for fu

ISSN:0277-6715    

DOI:10.1002/sim.4780110210

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

年代:1992

数据来源: WILEY

摘要:

AbstractScreening for a disorder may be carried out by assessing the risk that an individual is affected given the values of variables whose distributions alter when the disorder is present. An optimal screening policy is obtained by identifying those individuals whose risk is greater than some cut‐off value. This paper summarizes the way in which risk is derived from the likelihood ratio of being affected by the disorder, and compares three different methods of estimating the likelihood ratio, namely direct estimation, logistic regression and distribution modelling. For continuous variables that have a multivariate normal distribution, screening by risk is equivalent to the use of quadratic discrimination. The paper shows how estimates of the risk and associated detection and false positive rates can be derived for a screening policy which uses specified risk cut‐offs. Screening by risk has the counter‐intuitive property that as the separation in the distribution of screening variables between affected and unaffected individuals increases, the detection and false positive rates may both increase. The approach is explored using data on antenatal screening for Down's syndrome. The method of choice is model‐based; the model is described and tested for goodness of fit. Complications arising from outliers and non‐normality must be overcome before an appropriate assessment of risk can be made. The concept of shrinkage is used to estimate the detection and false positive rates that may be expected in a new

ISSN:0277-6715    

DOI:10.1002/sim.4780110211

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

年代:1992

数据来源: WILEY