摘要:

AbstractA simulation model is used to investigate the potential for indigenous spread of human immunodeficiency virus (HIV) in the heterosexual population in Norway. The heterosexual population is grouped according to age, sex and whether paired or single. Estimates of various parameters of sexual behaviour are taken from a population‐based questionnaire study. The questionnaire was sent to a random sample of 10,000 individuals, with a response rate of 63 per cent. The main simulation result is that with no inflow of infection from other risk groups, the heterosexual epidemic will decline if the average transmission probability per intercourse is 1 per cent or less. This result is insensitive to changes in the initial conditions. It is sensitive to changes in sexual behaviour, and to the shape of the transmission probability distribution. A review of empirical partner study data indicates an average transmission probability about 0.1 per cent per intercourse when no transmission modulating cofactors are present. It is concluded that with present sexual behaviour, the indigenous spread of HIV is not likely to sustain an epidemic in the Norwegian heterosexual populatio

ISSN:0277-6715    

DOI:10.1002/sim.4780100702

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe discuss the problem of describing multiple group comparisons in survival analysis using the Cox model, and in matched case‐control studies. The standard method of comparing the risk in each group with a baseline group is unsatisfactory because the standard errors and confidence limits relate to correlated parameters, all dependent on precision within the baseline group. We describe the construction of standard errors for the parameters of all groups, without the need to select a baseline group. These standard errors can be regarded as relating to roughly independent parameters, so that groups can be compared efficiently without knowledge of the covariances. The method should assist in graphical presentation of relative risks, and in the combination of results from published studies. Two examples are presente

ISSN:0277-6715    

DOI:10.1002/sim.4780100703

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

年代:1991

数据来源: WILEY

摘要:

AbstractLiang gave an extension of the Mantel‐Haenszel estimating procedure for a common odds ratio to logistic regression models. It is applicable to case‐control studies with multiple exposure levels, which yieldK2 ×Jtables. This paper provides variance and covariance estimators, which are consistent in both sparse‐data and large‐strata, for Liang's estimating functions in theK2 ×Jtables case, and proposes an approximate confidence interval method for the common od

ISSN:0277-6715    

DOI:10.1002/sim.4780100704

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe examine the relationship of age to mortality in blacks and whites in two cohort studies, the 20‐year follow‐up of the Evans County, Georgia, Study population and the 25‐year follow‐up of the Charleston Heart Study population. We conducted analyses with two parametric forms of hazard models (Gompertz and Weibull) for total mortality experience and considered the fit of the two hazard models in each study both separately and with the data pooled. We evaluated the robustness of conclusions about differences in the age pattern of mortality for blacks and whites by comparing results from the two hazard models. Where the tests were non‐nested, we used an information‐based statistic (AIC) to compare the fit of the models to the data. Results were robust to the selection of the hazard function, that is both models provided evidence that mortality rates at younger ages were lower for whilte than black females but that mortality rates increased more rapidly with age for white females. The absolute differences and the differences in the rates of increase were in the same direction, but smaller, for males. Though both models represented the general features of mortality patterns, the information statistic suggested better performance of the Gompertz function. The Gompertz function was also less sensitive to the initial age of determination of mortali

ISSN:0277-6715    

DOI:10.1002/sim.4780100705

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn a randomized clinical trial of the effect of prednisone versus placebo on survival in patients with liver cirrhosis, follow‐up visits were scheduled after 3,6 and 12 months of treatment and thereafter once a year. At each follow‐up theprothrombin index, a measure of liver function, was recorded and scored as either low or normal. The interaction between treatment and prothrombin index was analysed using a three‐state illness‐death model with recovery. The continuous‐time Markov process model with constant or piecewise constant intensities suggested by Kay allows inference to proceed even though the status of the disease indicator, here the prothrombin index, is only known at the time of each visit and not between visits. We compare the analysis with the theoretically incorrect, but practically rather common approximation, where the status of the disease indicator is assumed to remain constant from one visit until just before the next. Under this approximation both standard parametric methods and non‐parametric approaches developed by Aalen and Johansen ar

ISSN:0277-6715    

DOI:10.1002/sim.4780100706

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

年代:1991

数据来源: WILEY

摘要:

AbstractAlthough the traditional unrestricted ('non‐parametric') estimators of directly standardized rates and rate differences remain unbiased in sparse data, they tend to suffer from instability (low precision). As a result, many authors have proposed more precise estimators based on parametric models for the rates. This paper provides a general approach for constructing estimators of standardized parameters using generalized linear models, and shows that, in some common special cases, these model‐based ('smoothed') estimators can have an exceptionally simple f

ISSN:0277-6715    

DOI:10.1002/sim.4780100707

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

年代:1991

数据来源: WILEY

摘要:

AbstractThis paper considers the analysis of serial data on the growth of tumours in laboratory rodents. I propose a model ‐ a generalization of the tumour growth model of Norton and Simon ‐ that leads to a rich family of growth and decay curves. The model assumes that unperturbed growth follows the generalized logistic form; it accommodates time‐varying treatment effects through an effective dose function. I fit two such models to data on a human prostate tumour growing in nude mice and compare the fitted curves and dose functions with a non‐parametric curve and dose function estimated from a cubic spline model. All three models account for both random animal effects and autocorrelation. Monte Carlo results suggest that (a) maximum likelihood estimates of growth parameters are biased, although not severely, and (b) standard errors are conservative in small samples but become increasingly accurate in larger

ISSN:0277-6715    

DOI:10.1002/sim.4780100708

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

年代:1991

数据来源: WILEY

摘要:

AbstractThree methods for detecting the progression of periodontal disease based on the change in attachment level on teeth are compared from a statistical point of view. Regardless of gradual or burst disease progression theories, the regression method is found to be the most efficient way to detect changes. The exact false alarm rate is computed when the decision is based on the maximum regression coefficient at all sites during several visits.

ISSN:0277-6715    

DOI:10.1002/sim.4780100709

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

年代:1991

数据来源: WILEY

摘要:

AbstractClinical trials of new drugs in the treatment of angina pectoris frequently make use of exercise tests to evaluate efficacy. The crossover design is often employed. The methods commonly used to analyse the various exercise times, for example, ‘time to pain’, are insensitive and potentially biased by the manner in which they deal with the censored nature of the data. Survival analysis can be adapted for use in crossover trials, both in a relatively simple way, and also through the full power of the Cox model. This is considerably more sensitive and not subject to the same bias. This methodology leads to the use of median survival times to illustrate treatment effects and this provides a practical interpretation of clinical relevance. The estimation of median survival times in crossover trials poses some special problems. The methodology is illustrated throughout by means of a specific two‐period example in which atenolol was compared with the combination of atenolol and nifedipine. The three‐period design is also briefly di

ISSN:0277-6715    

DOI:10.1002/sim.4780100710

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

年代:1991

数据来源: WILEY

摘要:

AbstractFor cross‐over designs, we show that one can recover information on direct and/or residual treatment effects from an inter‐block (patients as blocks) analysis as is done in an incomplete block design.1By combining the intra‐ and inter‐block estimates, we obtain the generalized least squares estimate. In analysing cross‐over trials, we recommended this approach provided the between‐patient variance component can be estimated

ISSN:0277-6715    

DOI:10.1002/sim.4780100711

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

年代:1991

数据来源: WILEY