摘要:

AbstractWe compare two statistical methods for combining event rates from several studies. Both methods treat each study as a separate stratum. The Peto‐modified Mantel—Haenszel (Peto) method estimates a combined odds ratio assuming homogeneity across strata and provides a test for heterogeneity. The DerSimonian and Laird modified Cochran method (D&L) produces a weighted average of rate differences, where the weights allow for among‐study variability. We analyse 22 meta‐analyses from ten reports by both methods. The pooled estimates are divided by their standard errors to produce a Z‐statistic. At‐test comparingZ‐statistics from all 22 studies suggests that the D&L method tends to be more conservative [d(Peto—D&L) = 0.29,t= 2.53,p= 0.02]. For a subset of 14 non‐heterogeneous studies, the difference is smaller and non‐significant (d= 0.09,t= 0.72,p= 0.49). The results from the methods correlate well (r= 0.66 for all 22 studies,r= 0.95 for 14 non‐heterogeneous studies). Thus, the presence of heterogeneity influences our conclusion. We discuss the statistical and scientific implicati

ISSN:0277-6715    

DOI:10.1002/sim.4780080202

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

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper provides power formulae for historically controlled studies with survival time endpoints, and considers two designs. The first design involves no further follow‐up of control group subjects; the second design involves collection of additional information on control group subjects who had not failed at the time of design of the prospective portion of the study. The power functions differ from those for concurrently controlled studies, since, under the first design, the control group data are constant for purposes of power calculations, while under the second design, some of the control group data are constant while the remainder are random. I contrast the required duration of these studies with the required duration for comparable concurrently controlled studies under a wide range of condition

ISSN:0277-6715    

DOI:10.1002/sim.4780080203

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

年代:1989

数据来源: WILEY

摘要:

AbstractFactorial designs in clinical trials allow for the study of several medical treatments simultaneously. This paper distinguishes among different types of settings in which factorial designs are useful. For the experiment that involves investigation of several new or untested therapies, we introduce a model that incorporates rates of non‐compliance to therapy as well as various degrees of subadditivity of treatment effects. We compare the operating characteristics of the factorial under this model with those of competing designs and show that a modest negative interaction can considerably diminish the power to detect treatment effects in the factorial even in cases that have little power to detect this interaction. We urge, therefore, that designers of clinical trials with factorial layouts posit realistic estimates of interactions among treatments in order to assure adequate power to detect beneficial effects of treatmen

ISSN:0277-6715    

DOI:10.1002/sim.4780080204

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

年代:1989

数据来源: WILEY

摘要:

AbstractA major objective of studying populations exposed to low levels of radiation is provision of direct assessment of the adequacy of estimates of health risks obtained by extrapolation of data on populations exposed at high levels. Meeting this objective requires the use of statistical methods that fully utilize available exposure measurements, and that consider the extensive body of prior knowledge regarding radiation‐induced health effects. This paper describes various methods of analysis and illustrates the methods with data on workers at the Hanford Site. Special problems are discussed, with attention to comparability of estimates and confidence limits with those obtained from extrapolatio

ISSN:0277-6715    

DOI:10.1002/sim.4780080205

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

年代:1989

数据来源: WILEY

摘要:

AbstractWe applied a two‐stage random effects model to pulmonary function data from 31 sarcoidosis patients to illustrate its usefulness in analysing unbalanced longitudinal data. For the first stage, repeated measurements of percentage of predicted forced vital capacity (FVC%) from an individual were modelled as a function of time since initial clinical assessment. At the second stage, parameters of this function were modelled as a function of certain patient characteristics. We used three methods for estimating the model parameters: maximum likelihood; empirical Bayes; and a two‐step least‐squares procedure. Similar results were obtained from each, but we recommend the empirical Bayes, since it provides unbiased estimates of variance components. Results indicated that deterioration in FVC% is associated with a higher initial FVC% value and large numbers of both total cells and eosinophils in bronchoalveolar lavage at the initial assessment. Improvement is associated with higher values of pulmonary Gallium uptake at initial assessment and race. Blacks are more likely to improve than w

ISSN:0277-6715    

DOI:10.1002/sim.4780080206

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

年代:1989

数据来源: WILEY

摘要:

AbstractMeasures of chronic degenerative disease diffusion, such as incidence and prevalence rates, are a basic need for epidemiologists and others working in many fields of human sciences. Equations relating death probabilities to incidence and survival probabilities for chronic degenerative diseases are derived from a cohort point of view. A maximum likelihood approach is adopted for the estimation of incidence as a function of time related covariates. When time series of mortality data are available, the model can be used to describe and analyse levels and dynamics of morbidity. A trial application to lung and breast cancer is given for the province of Varese, Italy, where incidence data are available from the Lombardy Cancer Register.

ISSN:0277-6715    

DOI:10.1002/sim.4780080207

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

年代:1989

数据来源: WILEY

摘要:

AbstractWe carried out a simulation study to compare the performance of three algorithms (complete cases, ALLVALUE, and expectation maximization, EM) in estimating regression parameters and missing values for situations that have varying amounts of missing data, distributions (normal, mixture of normals and lognormal), patterns of incomplete data (random, related and censored), and degrees of correlational structure among the dependent and independent variables. We found that the EM and complete cases algorithms performed equally well regardless of the correlational structure, when the percentage of incomplete data was only 5 per cent. When this percentage increased to 25 per cent, the EM algorithm was generally best for estimation, but the complete cases algorithm was safe and conservative. This finding may be attributed to the study design, which required that the slopes be the same in the population of all cases, and in the population of complete cases. In addition, the one‐step imputing method (ALLVALUE) was competitive only for situations with weak correlational structure and/or little missing data. In that situation the bias caused with use of all available information was less than that caused with use of only complete cases. On the other hand, for imputation, the EM algorithm performed optimally, even in situations of censored or log‐normally distributed d

ISSN:0277-6715    

DOI:10.1002/sim.4780080208

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

年代:1989

数据来源: WILEY

摘要:

AbstractWe have derived the variance of an expected utility for a probability tree in medical decision analysis based on a Taylor series approximation of the expected utility as a function of the probability and utility values used in the decision tree. The resulting variance estimate is an algebraic expression of the variances associated with the probability and utility estimates used. We also derive expressions for the case where the input parameter estimates are not independent. We discuss the choice of input parameters and their variance estimates and give an example that compares two protocols for the treatment of chlamydial infection.

ISSN:0277-6715    

DOI:10.1002/sim.4780080209

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

年代:1989

数据来源: WILEY

ISSN:0277-6715    

DOI:10.1002/sim.4780080210

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

年代:1989

数据来源: WILEY

ISSN:0277-6715    

DOI:10.1002/sim.4780080211

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

年代:1989

数据来源: WILEY