ISSN:0277-6715    

DOI:10.1002/sim.4780141602

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

年代:1995

数据来源: WILEY

摘要:

AbstractKaplan—Meier curves provide descriptors of survival information for different subgroups within a data set. Investigators frequently use these figures for descriptive comparison of the effect of a particular measure upon survival. When subjects enter a study at different ages and age is associated with survival, it is often desirable to adjust survival information for age differences in the subgroups. This report discusses several methods for age‐adjustment of survival curves, including direct age‐adjustment and proportional hazard modelling with age as a cova

ISSN:0277-6715    

DOI:10.1002/sim.4780141603

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn elderly Framingham men and women, systolic blood pressure and cigarette smoking status, as well as a subject's age and sex, strongly influenced the risk of developing cardiovascular disease during ten years of follow‐up. Multivariable proportional hazards models were used to assess the roles of several primary risk factors and to examine their secondary effects. The first three factors were noted in both sexes, separately and combined, but the risk function for blood pressure was steeper in men than in women (hazard ratio, HR, 1·53 per 20 mmHg, 95 per cent confidence interval, CI, 1·33 to 1·75 in men; HR = 1·19, 95 per cent CI 1·07 to 1·33 in women). Systolic pressure measured ten years earlier also contributed to CVD risk (HR = 1·16 per 20 mmHg, 95 per cent CI 1·04 to 1·30), even after accounting for current level. Smoking was associated with a 64 per cent elevation in risk, male sex with a 51 per cent increase, and each 5 years increment in age with a 22 per cent increase. Body mass index measured 10 years ago had a modest association, but current body mass index did not. Among diabetic subjects, total serum cholesterol had an asymmetrical U‐shaped risk function, the risk increasing to either side of sex‐specific median values; diabetesper se, however, was not significant in the final model. In non‐diabetic subjects, there was little change in CVD risk up to the median cholesterol values and a modest increase thereafter. None of the risk functions w

ISSN:0277-6715    

DOI:10.1002/sim.4780141604

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

年代:1995

数据来源: WILEY

摘要:

AbstractA health risk appraisal function is a mathematical model designed to estimate the risk or probability of a person's mortality or morbidity for various diseases based upon risk factors such as age, medical history and smoking behaviour. The Framingham Study has contributed substantially to the development and use of these for endpoints such as mortality and incidence of coronary heart disease and other cardiovascular diseases. This paper discusses a methodology for the development of health risk appraisal functions when the number of potential risk factors is large and illustrates it with sex specific functions for nursing home institutionalization. The methodology involves grouping variables substantively into sets, applying principal component factor analysis and variable clustering to obtain substantively meaningful composite scores, ranking these in order of substantive importance, and then entering these with a hierarchical ordering into a Cox proportional hazard regression.

ISSN:0277-6715    

DOI:10.1002/sim.4780141605

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe purpose of this paper is to develop and apply a meta‐analysis methodology, that does not require patient‐level data, for comparing treatments in terms of quality‐of‐life‐adjusted survival. As a motivating example, we considered adjuvant chemotherapy for breast cancer. This therapy has been shown to offer an improvement in recurrence‐free and overall survival, especially for youger women, but its acute toxic effects discourage some physicians from prescribing it. To determine whether the benefit of adjuvant chemotherapy treatment outweighs its costs in terms of toxic effects, we performed a meta‐analysis of quality‐adjusted survival based on data from 1229 patients, 49 years of age or younger, randomized in eight clinical trials that compared chemotherapy versus no adjuvant systemic therapy. We conducted the meta‐analysis by performing a quality‐adjusted survival analysis known as a Q‐TWiST analysis on each trial. A Q‐TWiST analysis allows one to make treatment comparisons that incorporate differences in quality of life associated with various health states. In this analysis, we define as health states the periods of time patients spend: (i) with subjective toxic effects of chemotherapy; (ii) without symptoms of recurrence and toxicity, and (iii) following disease recurrence. We assigned weights to each health state which reflect their relative value in terms of quality of life and allowed them to vary in a sensitivity analysis. We then combined the individual trial results in a meta‐analysis, using a multivariate regression model, in such a way that we could easily perform an overall sensitivity analysis. Individual patient‐level data are not required to perform this meta‐analysis methodology if the individual Q‐TWiST analysis resul

ISSN:0277-6715    

DOI:10.1002/sim.4780141606

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

年代:1995

数据来源: WILEY

摘要:

AbstractGraphical methods are often used to check goodness‐of‐fit of models to data. It is common to plot residuals against a reference distribution so that when the model fits the data, the configuration should be close to a straight line. Since the resemblance to a straight line is often unclear, it has been suggested to add simulated envelopes within which the configuration is expected to lie. The implementation of this method for survival data analysis is not straightforward. In this paper we point out the difficulties which arise in constructing envelopes on residual plots for randomly censored data. Methods are suggested to deal with the problems and evaluated; they are illustrated by simulated data and on a follow‐up study of my

ISSN:0277-6715    

DOI:10.1002/sim.4780141607

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn order to compare the birth incidences of particular congenital abnormalities in different populations, it is often necessary to allow for the effects of maternal age. Three age‐adjusted indices are defined, based on analogous indices from the literature on mortality studies, namely, the Standardized Mortality Ratio, the Comparative Mortality Figure and Kerridge's Inverse Method. In most practical situations the differences between them are likely to be trival. However, the first index is maximally efficient under multiplicative risk models and is easily adjusted for incomplete data. The second is the only one to provide valid comparisons under additive, as well as multiplicative, models. The third has the advantage that it does not require a knowledge of the maternal age distribution of all births in the population. The use of the three indices is illustrated with published data on Down's syndrom

ISSN:0277-6715    

DOI:10.1002/sim.4780141608

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn vitrofertilization has been advocated as a possible treatment for male factor infertility. Using data collected on 154 men, conventional semen analysis and the hamster ova penetration test are compared with respect to their power in predicting the success of assisted conception. As performing the hamster test is more expensive than the semen analysis, we also investigate a combined strategy. It performs better than the discrimination based solely on the semen parameters, but does not lead to an improvement over the overall discriminatory power obtained from the hamster test alone.

ISSN:0277-6715    

DOI:10.1002/sim.4780141609

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

年代:1995

数据来源: WILEY

摘要:

AbstractWhen studying lifetimes of amalgam fillings, one is faced with the fact that each patient may contribute multiple survival data. This creates a dependence problem, and some methods for solving it are presented here. Analysis for individual patients with simple approaches for combining data is discussed first. Then a parametric frailty model is applied to analyse variation within and between patients. The results are presented in the form of an empirical Bayes estimate for each patient.

ISSN:0277-6715    

DOI:10.1002/sim.4780141610

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn this paper we formalize the problem of testing the one‐sided equivalence in the sensitivities of two medical diagnostic tests under a matched‐pair study design. We derive conditional and unconditional sample size formulae which are decreasing functions of the probability of being diagnosed by both tests. We calculate upper boundary and midpoint sample sizes. Results of a Monte Carlo simulation study that compares the proposed sample size formulae with that of Lachenbruch suggest that our midpoint conditional sample size is the best choice to obtain the desired power for the type of equivalence studies discussed in the pa

ISSN:0277-6715    

DOI:10.1002/sim.4780141611

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

年代:1995

数据来源: WILEY