Using Full Cohort Information to Improve the Estimation Efficiency of Marginal Hazard Model for Multivariate Failure Times in Case-Cohort Studies
Hongtao Zhang,
Haibo Zhou,
David Couper,
Jianwen Cai
Issue:
Volume 9, Issue 6, December 2021
Pages:
192-210
Received:
8 June 2021
Accepted:
2 December 2021
Published:
24 December 2021
Abstract: The case-cohort design is widely used in large cohort studies when it is prohibitively costly to measure some exposures for all subjects in the full cohort, especially in studies where the disease rate is low. To investigate the effect of a risk factor on different diseases, multiple case-cohort studies using the same subcohort are usually conducted. To compare the effect of a risk factor on different types of diseases, times to different disease events need to be modeled simultaneously. Existing case-cohort estimators for multiple disease outcomes utilize only the relevant covariate information in cases and subcohort controls, though many covariates are measured for everyone in the full cohort. Intuitively, making full use of the relevant covariate information can improve efficiency. To this end, we consider a class of doubly-weighted estimators for both regular and generalized case-cohort studies with multiple disease outcomes. The asymptotic properties of the proposed estimators are derived and our simulation studies show that a gain in efficiency can be achieved with a properly chosen weight function. We apply the proposed method to re-analyze a data set from Atherosclerosis Risk in Communities (ARIC) study to showcase the gain in efficiency. Concluding remarks and future researches are also discussed.
Abstract: The case-cohort design is widely used in large cohort studies when it is prohibitively costly to measure some exposures for all subjects in the full cohort, especially in studies where the disease rate is low. To investigate the effect of a risk factor on different diseases, multiple case-cohort studies using the same subcohort are usually conducte...
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Natural Gas Pipeline Transportation as the Thermodynamic Process
Vladimir Alekber Suleymanov
Issue:
Volume 9, Issue 6, December 2021
Pages:
211-215
Received:
22 November 2021
Accepted:
28 December 2021
Published:
30 October 2021
Abstract: A verification of commonly used approval in pipeline hydraulics is carried out that the work of friction forces performed at the movement of real gas on the gas pipeline completely turns into thermal energy. It is obvious that measurements of the actual temperature of the transported gas cannot confirm this hypothesis due to the inaccuracy of measurements of parameters affecting thermal processes in a real gas pipeline. The solution of the initial system of differential equations describing the 1-D process of stationary pipeline transportation of natural gas is considered as a serial set of values of thermobaric and rate flow parameters - pressure, temperature, velocity – of elementary volume of gas as it moves through the gas pipeline, that is, the Lagrangian approach is used in the study of the pipeline natural gas transport process. By means of integral definition of entropy by Clausius it is shown that the mentioned statement about the conversion of the work of the friction forces entirely into the thermal energy of the gas flow finds its confirmation with an accuracy acceptable for engineering applications in relation to the one-dimensional formulation of the problem of determining temperature of a gas along the length of pipeline.
Abstract: A verification of commonly used approval in pipeline hydraulics is carried out that the work of friction forces performed at the movement of real gas on the gas pipeline completely turns into thermal energy. It is obvious that measurements of the actual temperature of the transported gas cannot confirm this hypothesis due to the inaccuracy of measu...
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