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Re: st: left-truncation of entry in survival analysis
On 22 Márta 2006, at 12:46, Sue Chinn wrote:
One powerful argument for using age as the time variable in survival
analysis has to do with the hazard function itself. In modelling risk
factors or prognostic factors, the shape of the hazard function is
often treated as a high-dimensional nuisance parameter (I love that
expression and use it as often as I can). However, in risk estimation
the hazard function represents the absolute risk, without which the
hazard ratios cannot be interpreted in real-life terms.
So, am I missing something, or are advocates of the first model
deluding themselves? Can left truncation be ignored with age as the
Using age as the time variable allows the construction of hazard
functions spanning the age range from the youngest entry to the
oldest exit. It allowed us, in the SCORE project, to make
cardiovascular risk charts showing ten-year risk from datasets many
of which contained at most 8 years of follow up.
Since the publication of Ed Korn's paper, there have been a number of
papers looking to see if the modelling of risk factor effects is
affected by the choice of time metric and the short answer seems to
be 'not so you would notice'. I haven't been keeping up with the
literature on this, but I don't know of a case where someone got very
different results - does anyone else?
Korn's proposal appeals to my sense of elegance, as well as being a
gift to those of us who have to deal with absolute risks.
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