Re: st: Interval censored survival and stpm or intcens-correction

[Steven Samuels <sjhsamuels@earthlink.net>]

---

The original code was correct, the correction was not....
Although Sharon mentioned that examinations took place at six month  
intervals, I suggest she use the actual days on study as her time  
variable, not "month", as illustrated here.

-Steve

Here it is again.

Following is code which will convert -stset- multiple record 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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