ISSN:0277-6715    

DOI:10.1002/sim.4780101019

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

年代:1991

数据来源: WILEY

摘要:

AbstractDuring an investigation concerned with the relationship between air pollution and respiratory diseases in children, the ‘Schweizerhalle’ accident occurred when unknown amounts of pollutants were discharged into the environment. In that investigation, two series of medical data were collected during one year: (a) The daily relative number of preschool children, exhibiting diseases of the respiratory tract, who either came to the outpatients' clinic of the Children's Hospital or were reported by paediatricians in Basle; (b) The daily number of respiratory symptoms per child, observed in a group of randomly selected preschool children. The purpose of the present time series analysis is the assessment of possible change in these series after the environmental accident. The nature of the change is studied by complementary approaches. First, a forecast arising from models identified in the preaccident period is compared with the actual data. Thereafter, intervention models which adequately and parsimoniously represent the change are identified. Finally, an identification of a change‐point is perf

ISSN:0277-6715    

DOI:10.1002/sim.4780101002

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

年代:1991

数据来源: WILEY

摘要:

AbstractEpidemiological surveillance can be used to initiate preventive measures andSalmonellainfection is a prime example of application. It is important that any unusual increase of reported cases should be detected as rapidly as possible. Reliable forecasts based on a suitable model of the temporal structure of a pathological indicator are necessary for the elaboration of an alert threshold. We first discuss the specific problems associated with the identification and the estimation of the temporal structure of indicators of infectious diseases when they present both epidemic peaks and an underlying stationary structure. Then we consider how an alert threshold can be defined. Our application concerns infections caused byS. bovismorbificansin France for which an alert threshold is constructed and tested both retrospectively and prospectively.

ISSN:0277-6715    

DOI:10.1002/sim.4780101003

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

年代:1991

数据来源: WILEY

摘要:

AbstractGeneralized relative risk functions were used to model radiation dose‐response information from a large matched case‐control study of leukaemia occurring after treatment for cervical cancer. Models suggested by radiobiological theory were investigated and compared to standard analyses of categorical dose‐response to the linear model. Local radiation doses to each of fourteen bone marrow compartements for each patient were incorporated into the models, and the corresponding risks were summed. Conditional maximum likelihood methods were used to estimate risk parameters. Unique features of the analysis include modelling both induction and reduction of risk as a function of radiation dose absorbed by different parts of the body within individuals. Detailed statistical aspects of these analyses are presented and disc

ISSN:0277-6715    

DOI:10.1002/sim.4780101004

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe method of back‐projection has been used to estimate the unobserved past incidence of infection with the human immunodeficiency virus (HIV) and to obtain projections of future AIDS incidence. Here a new approach to back‐projection, which avoids parametric assumptions about the form of the HIV infection intensity, is described. This approach gives the data greater opportunity to determine the shape of the estimated intensity function. The method is based on a modification of an EM algorithm for maximum likelihood estimation that incorporates smoothing of the estimated parameters. It is easy to implement on a computer because the computations are based on explicit formulae. The method is illustrated with applications to AIDS data from Australia, U.S.A. and Japanese haemophili

ISSN:0277-6715    

DOI:10.1002/sim.4780101005

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn the pharmaceutical industry, an assay method is considered validated if the accuracy and precision for an assay meet some acceptable limits. This paper discusses the assessment of assay precision in terms of the estimation of total variability of an assay from a one‐way random effects model which is often considered in assay validation. We propose a general class of estimators that includes the analysis of variance estimator and the maximum likelihood estimator. We derive the optimal estimator, in terms of smallest mean squared error, within this class and consider an approximate version of this optimal estimator. We report on a Monte Carlo simulation to study its finite sample performance. We also present two examples to illustrate the use of the proposed methodolog

ISSN:0277-6715    

DOI:10.1002/sim.4780101006

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn testing the independence of the row and column variables in a two‐way contingency table, the standard Pearson and likelihood ratio chi‐square statistics often have low power, especially as the dimensions of the table increase. In this paper, one degree of freedom tests of independence based on likelihood ratio and score statistics from an association model for tables with nominal row and column classifications are described. The score statistic is especially easy to use, since it can be expressed in closed form, is simple to compute, and has size and power properties which are only slightly inferior to those of the more complicated likelihood ratio statis

ISSN:0277-6715    

DOI:10.1002/sim.4780101007

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe validity of statistical conclusions in medical research depends on proper analysis and interpretation of collected data. One potential area of invalidity is the inappropriatepost hocanalysis of statistically significant interactions in the analysis of variance of factorial designs. This paper examines the statistical explanations included in 83 studies published in three leading medical journals where the findings indicated significant interaction effects. Only 24 per cent of the reported statistically significant interactions had an accompanying correct interpretation. The most common form of misinterpretation involved a comparison of individual cell means within a row or column of one factor used in the design. This interpretation did not conform to the factorial ANOVA model with interaction. This misinterpretation occurs when the correct omnibus test of a hypothesis is followed by an incorrectpost hocanalysis and/or an inaccurate assessment of the original statistical result.

ISSN:0277-6715    

DOI:10.1002/sim.4780101008

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn a previous paper we defined the efficacy of a vaccine as 1 ‐ β1/β1, where β0is the instantaneous probability of transmission of infection to an unvaccinated person exposed to a single infectious person, and β1is similarly defined for a vaccinated person. We showed that under the conditions of an outbreak of an acute, directly transmitted infectious disease in a homogeneous and randomly mixing population, an estimate of this measure of vaccine efficacy is 1 ‐ [ln(1 ‐A1)/ln(1 ‐A0)], whereA0andA1are the observed final attack rates among unvaccinated and vaccinated persons, respectively. In the present work we present an approximation for the standard error of this estimator, accounting for both the sampling and process variation. We extend the results of our previous paper to a stratified population, where the strata correspond to different levels of susceptibility and may have different vaccination coverages. We also consider populations that consist of small units (for example, households) where individuals mix primarily in these units. In this case, definition of vaccine efficacy is in terms of the within‐unit transmission probabilities and is estimable by using transmission models for infectious diseases. We apply the estimation methods described above to data from influenza and measles outbreaks. We also examine, via a stochastic simulation study, the robustness of the vaccine efficacy estimators under various population structures and mi

ISSN:0277-6715    

DOI:10.1002/sim.4780101009

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

年代:1991

数据来源: WILEY

摘要:

AbstractIn the Physicians' Health Study, a randomized, placebo‐controlled, double‐blind trial of aspirin in the reduction of cardiovascular mortality and beta‐carotene in decreasing cancer incidence, 33,223 subjects were eligible and willing to enter the trial. Instead of randomizing this group immediately, all participants received identical calendar packs that contained active aspirin and beta‐carotene placebo. Following an 18‐week run‐in, only 22,071 subjects who remained eligible and willing and had taken at least 2/3 of their pills were randomized. We estimated the effect of the run‐in as follows: pill taking compliance increased 20‐41 per cent; sample size decreased 34 per cent; duration of follow‐up decreased 7 per cent which resulted in a 7 per cent decrease in the expected event rate for the placebo group. To estimate these changes, we made assumptions about compliance and outcome risk for those excluded by the run‐in. Our conclusion, however, about the net effect of the run‐in on the power of the study remains constant across variations in a number of those assumptions. The power with the run‐in, with 22,071 good compliers was typically higher, and never more than negligibly lower, than the power without the run‐in, with 33,223 good and poor compliers. In addition, savings from enrolling 11,152 fewer subjects in the trial resulted f

ISSN:0277-6715    

DOI:10.1002/sim.4780101010

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

年代:1991

数据来源: WILEY