摘要:

AbstractTo study the spread of sexually transmitted diseases (STDs) using social/sexual mixing models, one must have quantitative information about sexual mixing. An unavoidable complication in gathering such information by survey is that members of the surveyed population will almost certainly have sexual contacts outside that population. The number of these outsiders may be substantial and, hence, important for the modelling process. In this paper, we develop a mark‐recapture model for estimating the size of the population at risk for contracting a STD due to direct sexual contact with a specified population targeted by a survey. This mark‐recapture methodology provides a reliable method of estimating the number of outsiders. Because not everyone in the targeted population may be sexually active, the size of the sexually active subset, used as the number marked in our tag‐recapture formulation, must be estimated, which introduces extra variability. We derive an estimator of the variance of the estimated total number at risk that accounts for this extra variability and an expression for the bias of that estimator. We extend the methodology to stratified surveys and illustrate its use with data collected from a population of university undergraduates to estimate sexual mixing parameters of a deterministic model of the spread of

ISSN:0277-6715    

DOI:10.1002/sim.4780111202

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe detection of unusual patterns in health data presents an important challenge to health workers interested in early identification of epidemics or important risk factors. A useful procedure for detection of aberrations is the ratio of a current report to some historic baseline. This work addresses the problem of finding the variance of such a ratio when the surveillance reports are correlated. Results show that, when estimating this variance or the variance of the sample mean from a series of observations with an estimated correlation structure, bootstrap and jackknife estimates may be overly optimistic. The delta method or a classical method may be more useful when such model dependence is inappropriate.

ISSN:0277-6715    

DOI:10.1002/sim.4780111203

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

年代:1992

数据来源: WILEY

摘要:

AbstractDoubly censored data arise in some cohort studies of the AIDS incubation period because the time of infection may be known only up to an interval defined by two successive screening tests for HIV antibody. A simple analytic approach is to impute the infection time by the mid‐point of the interval and then apply standard survival techniques for right censored data. The objective of this paper is to investigate the statistical properties of such a mid‐point imputation approach. We investigated the asymptotic bias of the Kaplan‐Meier estimate, coverage probabilities of associated confidence intervals, bias in hazard ratio, and the size of the logrank test. We show that the statistical properties of mid‐point imputation depend strongly on the underlying distributions of infection times and the incubation periods, and the width of the interval between screening tests. In the absence of treatment, the median incubation period of HIV infection is approximately 10 years, and we conclude that, for this situation, mid‐point imputation is a reasonable procedure for interval widths of 2 year

ISSN:0277-6715    

DOI:10.1002/sim.4780111204

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

年代:1992

数据来源: WILEY

摘要:

AbstractIncidence, prevalence and mortality are commonly used measures to assess the impact of disease on human populations. Prevalence, although regularly assessed for a number of different diseases, has only had recent use to measure the impact of cancer. The calculation of the prevalence of cancer presents several difficulties since there is no reporting mechanism established to measure the proportion of the community that has the disease. In the absence of such a mechanism, mortality data linked to incidence data from cancer registries have been used. The assumption is made that once diagnosed with cancer an individual remains a prevalent case until death. In this paper we present alternatives to this assumption and use them to produce estimates of cancer prevalence. We illustrate the effect of these assumptions on the calculated prevalence of cancer using data from the British Columbia Cancer Registry.

ISSN:0277-6715    

DOI:10.1002/sim.4780111205

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

年代:1992

数据来源: WILEY

摘要:

AbstractA method is described for estimating prevalence by group testing using generalized linear models. This provides a simple way of analysing such data using widely available software. Existing methodology to correct for overdispersion using quasi‐likelihoods is applied to the group testing model. The methods are illustrated by an estimation of salmonella contamination in eggs, and of yellow fever virus infection in a mosquito populatio

ISSN:0277-6715    

DOI:10.1002/sim.4780111206

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe case‐cohort study design is a useful modification of the case‐control design, which allows direct estimation of the risk ratio without the rare‐disease assumption. While several risk ratio estimation procedures have been proposed under large‐strata settings, only the Mantel‐Haenszel point estimator is available in sparse stratifications. This paper provides simple confidence limits methods, based on the large‐sample distribution of the Mantel‐Haenszel risk ratio, that apply to both large‐strata and sparse‐data situations. For the Tarone risk ratio, I give a new large‐strat

ISSN:0277-6715    

DOI:10.1002/sim.4780111207

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

年代:1992

数据来源: WILEY

摘要:

AbstractIn group randomized studies, the sample size calculations are complicated by within group (worksite, community, etc.) correlation. We compare by simulation the moment method and the more standard ANOVA method of estimating the intraclass correlation. We find the former is less biased for a small to moderate number of clusters but the difference disappears when the appropriate degree of freedom is used for the ANOVA estimator. We propose a simulation approach for sample size determination and illustrate it with an example.

ISSN:0277-6715    

DOI:10.1002/sim.4780111208

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe Cox proportional hazards model always treats the last observation in a time ordered data set as an inexact survival time. In certain situations this can lead to this observation always having a low case influence and consequently never being highlighted by a case influence analysis. Thus an influential value can become non‐influential by a miscalculation of survival time and this, in turn, can affect conclusions of an analysis based on statistical significance (P‐valu

ISSN:0277-6715    

DOI:10.1002/sim.4780111209

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

年代:1992

数据来源: WILEY

ISSN:0277-6715    

DOI:10.1002/sim.4780111210

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

年代:1992

数据来源: WILEY

ISSN:0277-6715    

DOI:10.1002/sim.4780111211

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

年代:1992

数据来源: WILEY