摘要:

AbstractEpidemiologists have used the term ‘tracking’ to connote an individual's maintenance of relative rank of some longitudinally measured characteristic over a given time span. To assess the extent to which an attribute tracks we have first to summarize individual growth curves, and second to quantify the notion of maintenance of relative rank, both in the face of random error. A sequence of papers appearing in 1981 provided differing methodologies for appraising tracking. Here we take a different approach to tracking by using regression trees for longitudinal data. The above two concerns are simultaneously addressed in that the procedure identifies subgroups. defined in terms of covariates, within which the collection of growth curves is homogeneous. After reviewing the existing approaches to tracking we describe the tree‐structured methodology, and present an illustrative example pertaining to lung function growth in chi

ISSN:0277-6715    

DOI:10.1002/sim.4780122302

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

年代:1993

数据来源: WILEY

摘要:

AbstractMany studies collect longitudinal data but do not use them efficiently. We propose a technique for reducing a set of longitudinal data into four common summary statistics together with time. These statistics can be used in place of the raw data in further analyses, for example in a regression analysis. Instead of arbitrarily choosing the summary statistics, we derive them mathematically, thus justifying their use. This simplifies the subsequent analyses, and also improves the interpretation of the results. An example from the Framingham Heart Study illustrates the procedure.

ISSN:0277-6715    

DOI:10.1002/sim.4780122303

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

年代:1993

数据来源: WILEY

摘要:

AbstractA large data set of unsatisfactory smear rates from 629 different cervical smear takers is used to illustrate a Bayesian approach to the analysis of medical audit data with a binary outcome. It is shown that this gives more relevant results in terms of characterizing individual smear takers than frequentist methods, and that the full Bayesian analysis is preferable to an empirical Bayes approximation when the number of different smear takers is small and at least one individual smear taker has contributed only a few smears. Plots of Bayesian posterior distributions with 95 per cent confidence sets are suggested as a useful way of feeding back the results to individual clinicians.

ISSN:0277-6715    

DOI:10.1002/sim.4780122304

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

年代:1993

数据来源: WILEY

摘要:

AbstractChance‐corrected measures of agreement are prone to exhibit paradoxical and counter‐intuitive results when used as measures of reliability. It is demonstrated that these problems arise with Cohen's kappa as well as with Aickin's alpha. They are the consequence of an analogy to Simpson's paradox in mixed populations. It is further shown that chance‐corrected measures of agreement may yield misleading values for binary ratings. It is concluded that improvements in the design and the analysis of reliability studies are a pre‐requisite for valid and pertinent

ISSN:0277-6715    

DOI:10.1002/sim.4780122305

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

年代:1993

数据来源: WILEY

摘要:

AbstractSuppose that two graders classify all eyes in a sample of patients for the presence or absence of a specified abnormality. In the statistical analysis of the data, possible correlation between the observations in the right and left eyes should be taken into account. Recently, general methods have been developed to analyse grader agreement in rating paired body structures. In the present paper, an alternative procedure is proposed that utilizes existing formulae for the computation of )weighted( kappa and its standard error. In addition, the McNemar test is generalized to compare the probabilities of a positive judgement by the two graders.

ISSN:0277-6715    

DOI:10.1002/sim.4780122306

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn many clinical trials, data are monitored periodically by an external data monitoring committee )DMC(. Usually the frequency of these interim ‘looks’ at the data is prespecified. However, the progress of a clinical trial is unpredictable; often the schedule of looks must be modified. The Lan–DeMets procedure provides a spending function approach which does not require prespecification of the frequency or timing of interim looks. The procedure was developed based on the principle of a continuous Brownian motion process. In this paper we employ more elementary concepts to describe a procedure which is based upon the continuous monitoring of emerging data. The approach is flexible in that it applies to both continuous data monitoring and occasional interim monitoring. Examples are given from real clinical t

ISSN:0277-6715    

DOI:10.1002/sim.4780122307

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe type I error and power characteristics of the modifiedttest were compared with those of the generalizedttest. Results suggested that, in contrast to the generalizedttest, the modifiedttest can be seriously non‐robust to departures from population normality, with such departures often producing anti‐conservative results. Neither test held an absolute power advantage over the other when responses were from normal distributions, but the modifiedttest was generally more powerful for these conditions. In comparison with the pooled samplesttest, both tests were usually much more efficient when treatment caused increases both in mean response and between‐subject variance, and suffered only small disadvantages when between‐subject variance was unchanged by treatment. Given these results and other considerations, recommendations for use of these recently devised tests ar

ISSN:0277-6715    

DOI:10.1002/sim.4780122308

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

年代:1993

数据来源: WILEY

ISSN:0277-6715    

DOI:10.1002/sim.4780122309

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

年代:1993

数据来源: WILEY

ISSN:0277-6715    

DOI:10.1002/sim.4780122310

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

年代:1993

数据来源: WILEY

ISSN:0277-6715    

DOI:10.1002/sim.4780122311

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

年代:1993

数据来源: WILEY