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Re: st: Interval censored survival and stpm or intcens
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Sharon--
As you haven't responded, we don't know what error -stpm- issued. You
may not have defined the "leftvar" properly. Or, with only interval
data and a small number of intervals, -stpm- may not have enough
information to fit its flexible spline models. In that case, you
must use -intcens-, which fits parametric models. I suggest that you
fit all of the parametric models. If -intcens- supports
postestimation commands, you can compare the models with the Schwartz
BIC statistic (-estat ic-). Otherwise, compute BIC by hand.
Another option is Stephen Jenkin's program -pgmhaz8- for grouped
proportional hazards data, available from SSC.
Steven
Following is code which will convert your data to a form that -
intcens- can use.
/*************************CODE FOLLOWS ***************/
clear
drop _all
set more off
capture log close
log using sharon01, replace text
input id month status
1 0 0
1 6 0
1 12 1
2 0 0
2 6 0
2 12 0
2 18 1
3 0 0
3 6 0
3 12 0
end
/* First identify people with event */
egen event=max(status), by(id)
list
tempfile temp0
save `temp0'
/* Intervals for people with events */
/* Start of interval */
keep if status==0 & event==1
bysort id (month): keep if _n==_N
rename month t0
tempfile temp1
save `temp1'
list id status event t0 t1
/* End of interval */
use `temp0',clear
keep if status==1
bysort id (month): keep if _n==1
rename month t1
merge id using `temp1'
tab _merge
drop _merge
tempfile temp3
save `temp3'
list
/* Censored observations- no events */
use `temp0'
keep if event==0
egen t0=min(month), by(id)
bysort id: keep if _n==1
gen t1=.
drop month
/* Final data */
append using `temp3'
sort id
list id t0 t1
On Sep 7, 2007, at 12:42 AM, Sharon Minnick wrote:
Hello,
I have been attempting to analyze my interval censored survival
data with either stpm or intcens ado's (From SSC). Both programs
have been used in published papers (stpm: Royston and Parmar 2002;
intcens: Griffin et al 2006). However, unless I am missing
something, they don't seem able to handle multiple records per
subject. In my study, subjects are bled and their serology
checked at 6 month intervals. I want to be able to use the
intervals when they were negative (and at risk) as well as the
interval ending in seroconversion (or censoring) and I don't want
to make only one interval per subject where some intervals will
then be 2 or 3 years long. Does anyone have experience using either
of these ado's in such a situation?
My data is in the span format with multiple records per subject.
For each subject, _t0 is the first date of the span and _t is the
second date of the span. There are no gaps, so _t for the first
span is equal to _t0 for the second span.
In the intcens ado, the interval is specified as t0 and t1, there
is no subject identifier. Intcens does not use stset parameters so
I would lose some of the structure of my data.
For stpm, I have tried to define the left variable to specify that
the observations are interval-censored by using _t0 as the left
variable (which is < _t so according to the help file, when _d is
0, this will specify late entry at _t0 and right censoring at _t
and when d is 1, this will specify interval censoring with an event
in [_t0, _t]. I always receive the error message "
If anyone has used these ado files with interval censored data with
multiple records per subject, I would appreciate a note as to
whether or not it worked (and how to set it up).
Thanks!
Sharon Minnick
University of California at Davis
*
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Steven Samuels
[email protected]
18 Cantine's Island
Saugerties, NY 12477
Phone: 845-246-0774
EFax: 208-498-7441
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/