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Re: st: Survival analysis - specifying age as time

From   Ronán Conroy <>
Subject   Re: st: Survival analysis - specifying age as time
Date   Mon, 11 Apr 2005 16:22:45 +0100

Hugh Davies wrote:


My apologies for a rather simple question.....
It's not - this is a very interesting topic in survival analysis!

I am evaluating the effectiveness of an intervention on the incidence of occupational noise-induced hearing loss.

I am conducting a survival analysis, in which I wish to examine time-to-hearing-loss in my experimental vs. control groups. My hypothesis is that time-to-hearing loss will be longer in the experimental group.

Because age is major risk factor for hearing loss, I wish to use age as my “time” variable.
It comes down to whether age is a risk factor or a measure or exposure to risk. Ed Korn wrote a very good paper on this topic

Korn EL, Graubard BI, Midthune D. Time-to-event analysis of longitudinal follow-up of a survey: choice of the time-scale. American Journal of Epidemiology 1997;145(1):72-80.

In many situations it is wasteful to regard time elapsed before the person comes under observation as a risk factor - age - and time elapsed afterwards as analysis time.

Being able to use age as analysis time means that you can construct a lifetime hazard function spanning the age range of your data, not limited by your follow-up (assuming no age-period-cohort problems). I did this in the SCORE risk function for cardiovascular disease, which underlies the European Task Force recommendations. The result was 10-year risk estimates, despite the fact that almost half of the datasets in the analysis had less than 10 years of follow up. The rationale is discussed further in the paper

Conroy RM, Pyörälä K, Fitzgerald A, et al. Estimation of ten-year risk of fatal cardiovascular disease in Europe: the SCORE project. Eur Heart J 2003;24:987-1003.


Ronan M Conroy ( Senior Lecturer in Biostatistics Royal College of Surgeons Dublin 2, Ireland +353 1 402 2431 (fax 2764) -------------------- Just say no to drug reps

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