摘要:

AbstractWe compare parameter estimates from the proportional hazards model, the cumulative logistic model and a new modified logistic model (referred to as the person‐time logistic model), with the use of simulated data sets and with the following quantities varied: disease incidence, risk factor strength, length of follow‐up, the proportion censored, non‐proportional hazards, and sample size. Parameter estimates from the person‐time logistic regression model closely approximated those from the Cox model when the survival time distribution was close to exponential, but could differ substantially in other situations. We found parameter estimates from the cumulative logistic model similar to those from the Cox and person‐time logistic models when the disease was rare, the risk factor moderate, and censoring rates similar across the covariates. We also compare the models with analysis of a real data set that involves the relationship of age, race, sex, blood pressure, and smoking to subsequent mortality. In this example, the length of follow‐up among survivors varied from 5 to 14 years and the Cox and person‐time logistic approaches gave nearly identical results. The cumulative logistic results had somewhat largerp‐values but were substantively similar for all but one coefficient (the age‐race interaction). The latter difference reflects differential censoring rates by

ISSN:0277-6715    

DOI:10.1002/sim.4780080502

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

年代:1989

数据来源: WILEY

摘要:

AbstractWe present examples of the usage of regression trees for censored response via two real world datasets, one a rheumatoid arthritis survival study and the other a hip replacement study, and draw comparisons with the results of Cox proportional hazards modelling. The two methods pursue different goals. Motivation of the tree techniques is the desire to extract meaningful prognostic groups while the proportional hazards model enables assessment of the impact of risk factors. The methods are thus complementary. For the arthritis study the two techniques corroborate one another, although the flavour of the conclusions derived differ. For the hip replacement study, however, the regression tree approach reveals structure that would not emerge from a routine proportional hazards analysis. We also discuss the treatment of data analytic issues such as the handling of missing values and influence in the presence of non‐uniform censorin

ISSN:0277-6715    

DOI:10.1002/sim.4780080503

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

年代:1989

数据来源: WILEY

摘要:

AbstractWe describe the use of cubic splines in regression models to represent the relationship between the response variable and a vector of covariates. This simple method can help prevent the problems that result from inappropriate linearity assumptions. We compare restricted cubic spline regression to non‐parametric procedures for characterizing the relationship between age and survival in the Stanford Heart Transplant data. We also provide an illustrative example in cancer therapeutic

ISSN:0277-6715    

DOI:10.1002/sim.4780080504

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

年代:1989

数据来源: WILEY

摘要:

AbstractGroup sequential testing procedures have seen wide use in Phase II clinical trials. The sample proportion p̂ of responders is the commonly used estimator for the binomial response probabilityp.It can be shown that p̂ is the maximum likelihood estimator (MLE) ofp.It is well known that MLE can be in general (Whitehead1) and p̂ in particular (Dupont2) biased estimators, if their computation follows a group sequential procedure. In this paper we numerically investigate the bias of p̂. We find that the magnitude of the bias of p̂ is less than 0.025 in all cases we investigated. We apply the idea in Whitehead1to propose a bias‐adjusted estimator that reduces the bias substantially and reduces the mean square error as well in a certain range ofp.We also evaluate the uniformly minimum variance unbiased (UMVU) estimator. If one does not mind a bias of 0.025, one may find the sample proportion a suitable estimator forpbecause of its simplicity and easy explanation. If one is concerned with bias, the bias‐adjusted estimator may be a goo

ISSN:0277-6715    

DOI:10.1002/sim.4780080505

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

年代:1989

数据来源: WILEY

摘要:

AbstractWe propose a family of log‐linear models for ordinal data that contain parameters reflecting change patterns to compare treatments relative to change from baseline. Under the most general model, rates of change can depend not only upon the direction of change, but also upon the level of the baseline classification. We describe methods for selection of a parsimonious model and for tests of hypotheses concerning treatment differences. Interpretation of treatment differences in the follow‐up response profiles, within baseline strata, employs the concept of stochastic ordering. Data from two clinical trials illustrate the proposed proced

ISSN:0277-6715    

DOI:10.1002/sim.4780080506

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

年代:1989

数据来源: WILEY

摘要:

AbstractClinical trials commonly employ the titration design for certain drugs such as antihypertensives. In a Phase III trial the design has purposes distinct from those of a Phase I or II trial, as well as from those of a trial with a parallel design. In this paper we compare the titration design with the usual parallel design in their respective purposes for Phase III trials, explore the relevant questions addressed, and examine typical data from such trials. We also discuss work which focuses primarily on the Phase I or II titration trials. We formulate the problem in the framework of a one‐way contingency table augmented with incomplete data and obtain the maximum likelihood estimates of the parameters and their estimated variances/covariances via the EM algorithm. An example of a Phase III study of an antihypertensive agent illustrates the proposed procedur

ISSN:0277-6715    

DOI:10.1002/sim.4780080507

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe design of a clinical trial to establish the equivalence of two treatments differs from that of an efficacy trial. The conventional null hypothesis of equivalent treatment efficacy is replaced by a null hypothesis of inequivalence which must be tested by appropriate statistics. In addition, the maximum allowable value of the true difference between the efficacy of two equivalent treatments must be specified. In oncology, such a trial is necessary when a standard treatment is replaced by a new less toxic one of equivalent efficacy. The statistical formulation is one‐sided. A trial comparing two pre‐operative treatments in childhood nephroblastoma is presented here and analysed according to this methodol

ISSN:0277-6715    

DOI:10.1002/sim.4780080508

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

年代:1989

数据来源: WILEY

摘要:

AbstractWe develop two estimators of a common odds ratio Ψ for designs in which the investigator randomly assigns each of two clusters to interventions within strata. The estimators rely on an empirical adjustment for clustering to provide improved estimators of Ψ relative to the standard Woolf and Mantel—Haenszel estimators, respectively. The results of a simulation study show that the suggested adjustment improves the accuracy of both of these well‐known estimators under conditions likely to arise in practice. We find the clustered Woolf estimator as particularly effective in terms of mean squared error reduction. We also discuss interval estim

ISSN:0277-6715    

DOI:10.1002/sim.4780080509

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

年代:1989

数据来源: WILEY

摘要:

AbstractEvaluation of univariate quantitative diagnostic tests by strictly proper scoring rules is considered as an alternative to the traditional error rate measures. In principle, the posterior probability of disease as a function of the test value is estimated from training observations, and subsequently the score is assessed on a set of test samples. The same subjects may serve as training and test samples when the bootstrap procedure is applied for estimation of standard errors and correction of bias. The method is demonstrated using serum bile acids and bilirubin in patients with liver disease. The power for comparison of scores from two tests is compared with that from error rate measures for some typical situations.

ISSN:0277-6715    

DOI:10.1002/sim.4780080510

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

年代:1989

数据来源: WILEY

摘要:

AbstractWe examine Goodman and Kruskal's λ using Efron's approach to regression and analysis of variance (ANOVA) for zero‐one outcome data. For a binary response cross‐classified by a single nominal predictor, we present a computationally simple ANOVA table in which λ is analogous to Pearson'sR‐square. We characterize the relationship between λ and the commonly used apparent error rate in logistic regression, and show that λ is based implicitly on a prediction rule for a saturated model with classification level 0.5. This relationship suggests that we can correct the apparent error rate for chance by defining a natural generalization of λ that we call PRE, the proportional reduction in error. We illustrate the use of λ and PRE in an analysis of prognostic factors for one‐year survival in children with the acquired immunodeficiency sy

ISSN:0277-6715    

DOI:10.1002/sim.4780080511

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

年代:1989

数据来源: WILEY