ISSN:0277-6715    

DOI:10.1002/sim.4780060802

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.4780060803

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

年代:1987

数据来源: WILEY

摘要:

AbstractEarly detection of cancer by screening advances the date of diagnosis, but may or may not affect survival. To assess the survival benefit associated with early detection, one must estimate the distribution of time survived post lead‐time, that is, after the unknown date when clinical diagnosis would have occurred in the absence of screening. One can then compare the adjusted survival of screen‐detected cancer cases to other groups of cases not diagnosed by screening. This paper describes a model for the survival of screen‐detected cases, with a hazard function that depends on an individual's lead time, the duration of preclinical disease, and the time since diagnosis. The model is fitted to the ten year survival data from the 132 screen‐detected cases of breast cancer in the well‐known HIP (Health Insurance Plan of Greater New York) study. Comparison with the survival of several groups of cancer cases not detected by screening (interval cases arising clinically in persons previously screened, cases among persons who refuse screening, and cases among randomized controls not offered screening) yields various estimates of benefit. Use of the interval cases for comparison gives an estimate of about 21 breast cancer deaths prevented among 20, 166 women screened in the HIP study; use of the data from the randomized controls gives an estimate of about 25 prevented deaths. The former estimate derives from the screened group of women only, and so the same method of evaluation may also be applied to community screening programmes and other situations that do not entail rand

ISSN:0277-6715    

DOI:10.1002/sim.4780060804

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

年代:1987

数据来源: WILEY

摘要:

AbstractThe patterns of standardized mortality ratios (SMRs) with duration of follow‐up and duration of service which are characteristic of the healthy worker effect in occupational cohort studies have been simulated using models of selection and survivor effects. The models support current theories about the population dynamics which underlie the selection effect but highlight inadequacies in our understanding of the survivor effect. Several possible models were tested and methods of generating appropriate data are discussed. It is important that the healthy worker effect should be better understood as it can present so large a problem in the interpretation of occupational risk estimate

ISSN:0277-6715    

DOI:10.1002/sim.4780060805

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

年代:1987

数据来源: WILEY

摘要:

AbstractAn account is given of the analysis of data from 2 × 2 cross‐over trials which include baseline measurements. We show that most of the previously proposed methods can be incorporated into a general framework of least‐squares estimation with a simple linear model. A simple analysis based on ordinary least‐squares estimators is described which can be used with either two‐samplet‐tests and confidence intervals or with the corresponding non‐parametric procedures. It is shown how the use of generalized least‐squares estimators is equivalent to the use of covariance adjustment. These methods require no assumptions about the covariance structure of the measurements from each subject. The results of assessing the covariance structure present in examples of data from a number of trials are summarized. These results suggest that previously proposed simple covariance structures are unlikely to be appropri

ISSN:0277-6715    

DOI:10.1002/sim.4780060806

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

年代:1987

数据来源: WILEY

摘要:

AbstractStopping rules for a placebo controlled clinical trial of anticoagulants after acute myocardial infarction were evaluated by means of computer simulation for the case of five interim analyses. The trial will be terminated and the null hypothesis of no treatment effect rejected when the one‐sidedP‐value (logrank test) is lower than 0.005, 0.005, 0.005, 0.014, and 0.023 at the respective interim analyses, and 0.032 at final evaluation. This implies a total size α = 0.05 and a power close to that of fixed sample size testing. The trial will also be terminated, without rejecting the null hypothesis, when the one‐sidedP‐value exceeds 0.95, 0.88, 0.81, 0.74, and 0.67 at the respective interim analyses. This modification hardly affects size a

ISSN:0277-6715    

DOI:10.1002/sim.4780060807

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

年代:1987

数据来源: WILEY

摘要:

AbstractIn survival analysis, as in other branches of applied statistics, confirmatory analysis is often requested before an initial finding can be cleared of suspicion of being due just to mass significance. This paper points out that the special temporal structure of the classical clinical trial with staggered entry allows re‐use of the initial survivors by left‐truncating their remaining survival times. This procedure can often save a considerable amount of calendar time. The procedure is illustrated by data from the Danish Breast Cancer Cooperative Gr

ISSN:0277-6715    

DOI:10.1002/sim.4780060808

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

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper outlines some of the difficulties encountered when using independent Bayes as a statistical decision aid for acute abdominal pain. Methods of reducing the resultant problems are suggested. Restriction of the number of facets in the system reduces violation of the simplifying assumption of symptom independence without adversely affecting efficiency. Introduction of a realistic utility structure is investigated as is the potential transportability of the decision aid. Generalizations of the results are discussed and potential uses of medical decision aids are considered.

ISSN:0277-6715    

DOI:10.1002/sim.4780060809

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

年代:1987

数据来源: WILEY

摘要:

AbstractIn the study of monozygotic twins relative to disease and risk factors, particular interest focuses on the subset who are discordant for some suspected risk factor (for example, smoking), since such twins constitute a natural case‐control pair. In such studies, questionnaires designed to identify the status of all twin pairs are sometimes error prone and can yield misleading estimates of the concordance‐discordance ratios. Greater efforts to verify the characteristics ofapparentlydiscordant pairs than to verify those ofapparentlyconcordant pairs can result in the ‘unequal ascertainment’ fallacy.Using the results of a questionnaire with known error rates and the ‘apparent’ frequencies yielded, we present unbiased, maximum likelihood estimates of the ‘true’ proportions of concordant and discordant pairs. We also present approximate covariances among

ISSN:0277-6715    

DOI:10.1002/sim.4780060810

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.4780060801

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

年代:1987

数据来源: WILEY