Re: st: AGE at event occurrence as the time variable in mortality analysis rather than time between entry into follow up an event occurrence

[Steven Samuels <sjhsamuels@earthlink.net>]

1. Svend and Maarten's advice for setting age as the time variable is  
still good.

2. You could add time from entry as a time-dependent covariate.  
However I suggest that  you enter it in the form Z = age at entry. If  
Y is current age, then Y - Z is time from entry: the three are  
collinear.  Age at entry is also equivalent to year of birth.   
Expressed in that way, it might capture some interesting effects of  
birth during wartime.

3. The risk sets of long-term survivors may be different genetically  
from the earlier risk sets--hardier, for example.  This is the  
problem of heterogeneity.  I suggest you employ one of the  frailty  
options in -stcox-.

-Steve



On Sep 7, 2008, at 1:17 PM, uri goldbourt wrote:


> Thanks.
>
> I may have provided an incomplete explanation of the issue.
> I have now 42 year mortality follow up of a cohort of men who had been
> tenured civil servants and municipal employees in 1962.
> In earlier analyses I always worked with time between entry (all  
> entered in
> 1963 and early 1964, spread over 14 month) and date of event. Even  
> 23 yr
> mortality we analyzed in this manner.
>
> With this new follow up, where 8471 of the original 10059 men have  
> died, I
> thought it more sensible to replace time till event (from entry) by  
> age (or
> time since birth' as you say) as the time variable. But the  
> original sample
> is not after "weeding out the high risk men" because they were aged  
> 40-65 at
> entry. I suppose this seems to justify handling the stset situation  
> ignoring
> left censoring. I ask, technically, whether I define the time variable
> separately or include it anywhere in the stset statement?
>
> Left censoring does, however, certainly plays a central role when I  
> limit
> analysis to survivors by 2000 (when everyone had either died or  
> reached age
> 80), because only for them we have information on dementia (mostly  
> Alzheimer
> disease) assessed on 2000 and we want to know how. for them.  
> parameters
> assessed long before, at mid-life [clinical, biochemical,  
> anthropometric,
> social] were related to the age at death between 2000 and 2006.
>
> UG
> ------------------------------------
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Maarten  
> buis
> Sent: Sunday, September 07, 2008 9:49 AM
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: AGE at event occurrence as the time variable in  
> mortality
> analysis rather than time between entry into follow up an event  
> occurrence
>
> --- uri goldbourt <goldbu1@post.tau.ac.il> wrote:
>
> > In an epidemiological study where we follow up very old individuals
> > the importance of time till event (say, mortality) pales in
> > comparison to the actual age of the individual when the endpoint
> > event occurred. <snip> What is the accurate way to stset the data so
> > that age at event(assuming of course it is included for each event)
> > become the time variable?
> Setting time is the easy part of your analysis: The age is nothing
> other than the time elapsed since birth. In your case the problem is
> left censoring: People could have experienced the event before  
> entering
> the study. As a consequence you have ended up with a selected sample
> where the weaklings have already been weeded out. I have never done a
> study where I had to deal with left censoring, so I don't remember if
> Stata can do anything about that and my books are at the office.
>
> -- Maarten
>
>
>
> -----------------------------------------
> Maarten L. Buis
> Department of Social Research Methodology
> Vrije Universiteit Amsterdam
> Boelelaan 1081
> 1081 HV Amsterdam
> The Netherlands
>
> visiting address:
> Buitenveldertselaan 3 (Metropolitan), room Z434
>
> +31 20 5986715
>
> http://home.fsw.vu.nl/m.buis/
> -----------------------------------------
>
>
>
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
>
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/