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A reference relative time-scale as an alternative to chronological age for cohorts with long follow-up

BACKGROUND: Epidemiologists have debated the appropriate time-scale for cohort survival studies; chronological age or time-on-study being two such time-scales. Importantly, assessment of risk factors may depend on the choice of time-scale. Recently, chronological or attained age has gained support b...

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Autor principal: Hurley, Margaret Anne
Formato: Online Artículo Texto
Lenguaje:English
Publicado: BioMed Central 2015
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4684933/
https://www.ncbi.nlm.nih.gov/pubmed/26691876
http://dx.doi.org/10.1186/s12982-015-0043-6
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author Hurley, Margaret Anne
author_facet Hurley, Margaret Anne
author_sort Hurley, Margaret Anne
collection PubMed
description BACKGROUND: Epidemiologists have debated the appropriate time-scale for cohort survival studies; chronological age or time-on-study being two such time-scales. Importantly, assessment of risk factors may depend on the choice of time-scale. Recently, chronological or attained age has gained support but a case can be made for a ‘reference relative time-scale’ as an alternative which circumvents difficulties that arise with this and other scales. The reference relative time of an individual participant is the integral of a reference population hazard function between time of entry and time of exit of the individual. The objective here is to describe the reference relative time-scale, illustrate its use, make comparison with attained age by simulation and explain its relationship to modern and traditional epidemiologic methods. RESULTS: A comparison was made between two models; a stratified Cox model with age as the time-scale versus an un-stratified Cox model using the reference relative time-scale. The illustrative comparison used a UK cohort of cotton workers, with differing ages at entry to the study, with accrual over a time period and with long follow-up. Additionally, exponential and Weibull models were fitted since the reference relative time-scale analysis need not be restricted to the Cox model. A simulation study showed that analysis using the reference relative time-scale and analysis using chronological age had very similar power to detect a significant risk factor and both were equally unbiased. Further, the analysis using the reference relative time-scale supported fully-parametric survival modelling and allowed percentile predictions and mortality curves to be constructed. CONCLUSIONS: The reference relative time-scale was a viable alternative to chronological age, led to simplification of the modelling process and possessed the defined features of a good time-scale as defined in reliability theory. The reference relative time-scale has several interpretations and provides a unifying concept that links contemporary approaches in survival and reliability analysis to the traditional epidemiologic methods of Poisson regression and standardised mortality ratios. The community of practitioners has not previously made this connection.
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spelling pubmed-46849332015-12-21 A reference relative time-scale as an alternative to chronological age for cohorts with long follow-up Hurley, Margaret Anne Emerg Themes Epidemiol Methodology BACKGROUND: Epidemiologists have debated the appropriate time-scale for cohort survival studies; chronological age or time-on-study being two such time-scales. Importantly, assessment of risk factors may depend on the choice of time-scale. Recently, chronological or attained age has gained support but a case can be made for a ‘reference relative time-scale’ as an alternative which circumvents difficulties that arise with this and other scales. The reference relative time of an individual participant is the integral of a reference population hazard function between time of entry and time of exit of the individual. The objective here is to describe the reference relative time-scale, illustrate its use, make comparison with attained age by simulation and explain its relationship to modern and traditional epidemiologic methods. RESULTS: A comparison was made between two models; a stratified Cox model with age as the time-scale versus an un-stratified Cox model using the reference relative time-scale. The illustrative comparison used a UK cohort of cotton workers, with differing ages at entry to the study, with accrual over a time period and with long follow-up. Additionally, exponential and Weibull models were fitted since the reference relative time-scale analysis need not be restricted to the Cox model. A simulation study showed that analysis using the reference relative time-scale and analysis using chronological age had very similar power to detect a significant risk factor and both were equally unbiased. Further, the analysis using the reference relative time-scale supported fully-parametric survival modelling and allowed percentile predictions and mortality curves to be constructed. CONCLUSIONS: The reference relative time-scale was a viable alternative to chronological age, led to simplification of the modelling process and possessed the defined features of a good time-scale as defined in reliability theory. The reference relative time-scale has several interpretations and provides a unifying concept that links contemporary approaches in survival and reliability analysis to the traditional epidemiologic methods of Poisson regression and standardised mortality ratios. The community of practitioners has not previously made this connection. BioMed Central 2015-12-18 /pmc/articles/PMC4684933/ /pubmed/26691876 http://dx.doi.org/10.1186/s12982-015-0043-6 Text en © Hurley. 2015 Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
spellingShingle Methodology
Hurley, Margaret Anne
A reference relative time-scale as an alternative to chronological age for cohorts with long follow-up
title A reference relative time-scale as an alternative to chronological age for cohorts with long follow-up
title_full A reference relative time-scale as an alternative to chronological age for cohorts with long follow-up
title_fullStr A reference relative time-scale as an alternative to chronological age for cohorts with long follow-up
title_full_unstemmed A reference relative time-scale as an alternative to chronological age for cohorts with long follow-up
title_short A reference relative time-scale as an alternative to chronological age for cohorts with long follow-up
title_sort reference relative time-scale as an alternative to chronological age for cohorts with long follow-up
topic Methodology
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4684933/
https://www.ncbi.nlm.nih.gov/pubmed/26691876
http://dx.doi.org/10.1186/s12982-015-0043-6
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