摘要:

AbstractWe present a method to determine the number of subjects,k, and number of repeated measurements,n, that minimize the overall cost of conducting a reliability study, while providing acceptable power for tests of hypotheses concerning the reliability coefficientp.Tables showing optimal choices ofkandnunder various cost constraints also appear. We discuss design considerations for reliability studies in light of the results.

ISSN:0277-6715    

DOI:10.1002/sim.4780060602

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

年代:1987

数据来源: WILEY

摘要:

AbstractStandard multiple comparison techniques do not adequately address the situation in which one must demonstrate a combination therapy's superiority to both of its components. This paper proposes several alternative tests to deal with this situation, and evaluates the tests with a Monte Carlo sampling experiment that compares the actual with the nominal significance levels of the tests. Data from a clinical trial that compares the efficacy of a combination analgesic/muscle relaxant to its components and placebo in the treatment of low back pain and spasm illustrate the tests.

ISSN:0277-6715    

DOI:10.1002/sim.4780060603

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

年代:1987

数据来源: WILEY

摘要:

AbstractWe have applied the technique of Monte Carlo simulation to the determination of sample size for a partially completed clinical trial of chemotherapy for breast cancer. Simulations based on results observed after the entry of 243 patients in 2 years indicated a power greater than that predicted by the calculations made before the protocol was activated, and allowed a recommendation for an eventual trial closure earlier than would have been permitted by traditional methods. Both estimative and predictive approaches to the simulation of expected survival times for censored patients are presented. The use of simulation is recommended as an aid in reassessing the exact nature of the underlying survival distributions (as these affect the sample size calculations) and in optimizing stopping rules relating to patient accrual to a clinical trial in progress.

ISSN:0277-6715    

DOI:10.1002/sim.4780060604

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

年代:1987

数据来源: WILEY

摘要:

AbstractWe examine various methods to estimate the effective sample size for construction of confidence intervals for survival probabilities. We compare the effective sample sizes of Cutler and Ederer1and Petoet al.,2as well as a modified Cutler‐Ederer effective sample size. We investigate the use of these effective sample sizes in the common situation of many censored observations that intervene between the time point of interest and the last death before this time. We note that there is noa priorireason to treat upper and lower confidence intervals in a symmetric fashion since censored survival data are by nature asymmetric. We recommend the use of the Cutler‐Ederer effective sample size in construction of upper confidence intervals and the Peto effective sample size in construction of lower confidence intervals. Two examples with real data demonstrate the differences between confidence intervals formed with different effective sample sizes. This study also illustrates the need for caution in the application of simulation studies to real probl

ISSN:0277-6715    

DOI:10.1002/sim.4780060605

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

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper examines the problem of hypothesis testing for comparison of time‐dependent recurrent events between categorical exposure groups. We compare three methods (a summary chi‐square test based on a generalization of the simple Poisson distribution, a chi‐square test based on a generalization of the compound Poisson distribution, and a test on risk scores based on individual observed to expected ratios), when the dependent variable may be autocorrelated within an individual, and disease risk may be heterogeneous among subjects. We present a simulation study and an application to a cohort of sickle cell anaemia patients. With autocorrelation or heterogeneous risk present, the simple chi‐square test is inappropriate, while the other two methods perform well. An attraction of the risk score method is its relative ease of appl

ISSN:0277-6715    

DOI:10.1002/sim.4780060606

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

年代:1987

数据来源: WILEY

摘要:

AbstractA number of variance formulae for the attributable fraction have been presented, but none is consistent in sparse data, such as found in individually matched case‐control studies. This paper employs Mantel–Haenszel estimation to derive variance estimators for attributable fractions that are dually consistent, that is, consistent in both sparse data and large strata. The method may also be applied using conditional maximum likelihood. Extensions of these estimators to situations involving effect modification and preventive exposures are also derived. Examples of applications to individually matched case‐control studies are

ISSN:0277-6715    

DOI:10.1002/sim.4780060607

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

年代:1987

数据来源: WILEY

摘要:

AbstractJapanese researchers have reported that recent mortality rates from diabetes mellitus, ischemic heart disease, peptic ulcer, cirrhosis of the liver and suicide for middle‐aged Japanese men have increased by comparison with those for other age groups. There has been some controversy over the etiology of this unusual trend, and in particular whether it is due primarily to recent undesirable socio‐economic factors (period effects) or to factors specific to these cohorts born in the early Showa Era, around 1925 to 1940 (cohort effects). A possible source of this controversy lies in the methods which have been used to describe the trends; these are mostly descriptive and graphical.To elucidate which factors are responsible for these trends, we analysed the mortality data quantitatively applying an age‐period‐cohort model modified so that period effects remain constant within certain age groups but may vary from one age group to the next. Although the identifiability problem still occurs in the modified model, estimable curvature components of time effects may be used to examine these unusual trends. In fact, the peculiarity of the cohort born in the early Showa Era was clearly detected by the curvature components of cohort effects for these major diseases. These findings are consistent with the ‘cohort hypothesis’ for the recent peculiar trend in Japanese mal

ISSN:0277-6715    

DOI:10.1002/sim.4780060608

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.4780060609

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.4780060601

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

年代:1987

数据来源: WILEY