Biomedical subjects

O Borgan

Publications and source records attributed to O Borgan.

9 recordsLinked to original sources

PubMed2000

Exposure stratified case-cohort designs.

A variant of the case-cohort design is proposed for the situation in which a correlate of the exposure (or prognostic factor) of interest is available for all cohort members, and exposure information is to be collected for a case-cohort sample. The cohort is stratified according to the correlate, and the subcohort is selected by stratified random sampling. A number of possible methods for the analysis of such exposure stratified case-cohort samples are presented, some of their statistical properties developed, and approximate relative efficiency and optimal allocation to the strata discussed. The methods are compared to each other, and to randomly sampled case-cohort studies, in a limited computer simulation study. We found that all of the proposed analysis methods performed well and were more efficient than a randomly sampled case-cohort study.

Biometry↗

PubMed1999

Aalen's linear model for sampled risk set data: a large sample study.

Borgan and Langholz (1997) describe a method for estimating the parameter functions in Aalen's linear hazard regression model from sampled risk set data. Using a counting process formulation and the martingale central limit theorem, we provide a study of the asymptotic distributional properties of the estimator. The results are applied to study the efficiencies of the nested case-control and counter-matched designs relative to a full cohort analysis.

Case-Control Studies↗

PubMed1997

Estimation of excess risk from case-control data using Aalen's linear regression model.

We introduce methods for statistical inference in Aalen's non-parametric linear regression model of disease incidence (Aalen, 1989, Statistics in Medicine 8, 907-925) from nested case-control data. These methods provide the basis for estimation of excess risk as a linear function of dose and absolute risk for a given exposure history. The methods are illustrated by estimating excess and absolute risks associated with radon exposure and smoking from nested case-control samples from the Colorado Plateau uranium miners cohort.

Adult↗

PubMed1997

Estimation of absolute risk from nested case-control data.

Benichou and Gail (1995, Biometrics 51, 182-194) describe methods for estimating the absolute risk of developing disease given a set of covariate values over a specified time interval from a case-control study within a cohort. The methods are most suitable for unmatched case-control studies, and are restricted to categorical covariates. Expanding on methods for estimating relative mortality from nested case-control studies presented in Borgan and Langholz (1993, Biometrics 49, 593-602), we present methods for estimating absolute risk from individually matched nested case-control data. These methods accommodate continuous and time-dependent covariate histories, the sampling of cases, and various control sampling designs.

Adult↗

PubMed1996

A method for checking regression models in survival analysis based on the risk score.

We propose to perform model check for the Cox and Aalen regression models using martingale residual processes grouped after the risk score. Asymptotic distributions of the grouped martingale residual processes are deduced, so both formal and graphical model check can be performed. The method is validated by stochastic simulation. A data example with patients with primary biliary cirrhosis of the liver is discussed.

Humans↗

PubMed1993

Nonparametric estimation of relative mortality from nested case-control studies.

Andersen et al. (1985, Biometrics 41, 921-932) gave an estimator of the cumulative relative mortality comparing rates of death in an epidemiologic cohort to an external population as a function of time when covariate information is available on all cohort members. We present an analogous estimator when covariate information is known only on a nested case-control sample. Counting process techniques are used to show that this estimator is almost unbiased and an estimator of its variance is derived. Estimators of the relative mortality function, using kernel smoothing methods, and the average relative mortality over grouped time intervals are also presented. The methods are illustrated by comparing rates of lung cancer mortality in a cohort of Montana smelter workers to that in the United States population.

Case-Control Studies↗

PubMed1984

Efficiencies of experimental designs for an illness-death model.

Disease development is described by the progressive Markov illness-death model with one disease. The efficiencies of four experimental designs are discussed: the simple survival experiment, serial sacrifice, periodic diagnosis and complete observation. The discussion is based on the 'semiparametric' assumption of piecewise-constant intensities. Simple survival experiments are shown to have very low efficiency, serial sacrifice experiments to be moderately efficient, and periodic diagnosis to be almost as efficient as complete observation. An application to the analysis of the development of leukaemia in laboratory mice is given.

Animals↗

PubMed1983

Decreasing leukemia risk in old AKR mice.

Leukemia incidence and survivorship were studied in 480 untreated adult female AKR mice using repeated blood testing on live animals and autopsy for diagnosis. The data were statistically analysed within the framework of a Markov illness-death model. The leukemia risk was close to zero below an age of four-five months, increased sharply to a maximum at eight-nine months, and then declined markedly. Old AKR mice therefore should be useful for studies of age dependent alterations that reduce the risk of leukemia development. The observed age-dependence of the leukemia risk is at variance with the simplest version of the multistep hypothesis. Allowing for individual tendencies for leukemia development, good correlation between expected and observed values can be obtained.

Age Factors↗

PubMed1982

Nickel allergy and hand dermatitis in a stratified sample of the Danish female population: an epidemiological study including a statistic appendix.

The occurrence of nickel allergy and hand eczema has been investigated in a stratified sample (2 500) of the Danish female population by an interview technique. The incidence density (allergy intensity) has been estimated by standard maximum likelihood methods. The age-specific prevalence rates have been calculated by life table techniques. The incidence density has doubled in all age groups from 1948 to 1973. The highest prevalence rate of nickel allergy was found in the 45-year-olds (0.189 +/- 0.023). The possible interaction between nickel allergy and hand eczema was analysed by a Markov chain model. Compared with non-nickel-sensitive women, a woman who has become nickel sensitized ran an increased risk of developing hand eczema. And those who had first developed hand eczema ran an increased risk of subsequently developing nickel allergy. In future efforts to reduce direct skin contact with nickel, the close relation between nickel allergy and hand eczema should be the main argument. Statistical methods based on the incidence density will be useful in the evaluation of these efforts.

Adolescent↗