Biomedical subjects

Ørnulf Borgan

Publications and source records attributed to Ørnulf Borgan.

3 recordsLinked to original sources

PubMed2006

Dynamic path analysis-a new approach to analyzing time-dependent covariates.

In this article we introduce a general approach to dynamic path analysis. This is an extension of classical path analysis to the situation where variables may be time-dependent and where the outcome of main interest is a stochastic process. In particular we will focus on the survival and event history analysis setting where the main outcome is a counting process. Our approach will be especially fruitful for analyzing event history data with internal time-dependent covariates, where an ordinary regression analysis may fail. The approach enables us to describe how the effect of a fixed covariate partly is working directly and partly indirectly through internal time-dependent covariates. For the sequence of times of event, we define a sequence of path analysis models. At each time of an event, ordinary linear regression is used to estimate the relation between the covariates, while the additive hazard model is used for the regression of the counting process on the covariates. The methodology is illustrated using data from a randomized trial on survival for patients with liver cirrhosis.

Aged↗

PubMed2005

Lung transplantation in patients with chronic obstructive pulmonary disease in a national cohort is without obvious survival benefit.

BACKGROUND: The objective in lung transplantation is to prolong life, but the survival effect in patients with chronic obstructive pulmonary disease (COPD) or alpha1-anti-trypsin deficiency emphysema is still unresolved. This study assesses the impact of diagnosis, single-lung transplantation (SLT) vs bilateral lung transplantation (BLT) and timing of transplantation on survival in a national cohort. METHODS: In 219 consecutive patients accepted onto the lung transplantation waiting list in Norway, 1990 to 2003, we assessed predictors of death: (1) on the waiting list; (2) 90 days after transplantation. For each period we used Cox regression, including age, gender, diagnosis, baseline pulmonary function tests, cardiac catheterization data, exercise capacity and transplant type, as potential predictors. Survival benefit was assessed graphically by combining adjusted survival curves after transplantation with the curve for those waiting, modeling transplantation after 6, 12 or 24 months. RESULTS: Mean patient age was 49 years (SD 10), with 55% women. High forced expiratory volume in 1 second (FEV(1)) percentage predicted death on the waiting list. Diagnoses other than COPD/emphysema and receiving SLT were associated with death 90 days after transplantation. In COPD/emphysema, there was no clear survival benefit from BLT or SLT. For patients in the "Other" group, the data suggest a survival benefit from BLT. CONCLUSIONS: In COPD/emphysema, there was no obvious survival benefit from lung transplantation, which questions prolongation of life as the primary motivation for the procedure.

Adult↗

PubMed2002

Estimation of covariate-dependent Markov transition probabilities from nested case-control data.

Multi-state models are used to describe situations where individuals may move among a finite number of states defined by specific conditions of health, including death. The transition intensities of the models are described by proportional hazards models, and it is reviewed how estimation of the regression parameters and the baseline transition intensities may be performed when only nested case-control data are available for all or some of the transitions. The regression parameter estimates and the estimates of baseline transition intensities are combined to give estimates of the integrated transition intensities for specified covariate histories, and from these estimates covariate-dependent Markov transition probabilities are derived.

Analysis of Variance↗