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st: stset interval truncation and gaps in duration format


From   "Hugh Robinson" <hugh.robinson@umontana.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: stset interval truncation and gaps in duration format
Date   Mon, 7 Apr 2008 19:29:21 -0600

Hello,

I am using Stata for the first time, trying to analyze cougar survival
data.

I'm not sure if I am using stset properly with regards to animals with
gaps in their telemetry record (I used snapspan to convert radiotelemtry
data into a duration format encounter record).  In a single "event"
column I have coded capture==1, location/observation==2, and
mortality==3.  Animals were added in a staggered entry design over the
duration of the study from Jan 1 1998 to Jan 1 2007.  I've tried the
stset command below.

 stset date1, id(lion_id) failure(event==3) enter(event==1) exit(time
d(01Jan2007)) origin (time d(01Jan1998))

I would like Animals that were not located for more than 90 days to be
treated as "gaps" and coded their reentry as a second capture
(event==1).  My problem is Stata finds the earliest "enter" event and
calculates t0 from there (example below).  

Can someone tell me how to allow gaps with this kind of duration format?

Thanks
HR

lion_id loc_method event date 	date1 	date0 	_st	_d 	_t
_t0
F71	Capture	1	25/2/2003	25-Feb-03	.
0			
F71	VHF Aerial	2	17/3/2003	17-Mar-03
25-Feb-03	1	0	1901	1881
.	.	.	.	.	.	.	.	.
.	.	.
.	.	.	.	.	.	.	.	.
.	.	.
F71	VHF Aerial	2	7/4/2003	7-Apr-03	4-Apr-03
1	0	1922	1919
F71	VHF Aerial	2	10/4/2003	10-Apr-03	7-Apr-03
1	0	1925	1922
F71	VHF Aerial	2	16/4/2003	16-Apr-03
10-Apr-03	1	0	1931	1925
F71	Reencounter	1	6/2/2006	6-Feb-06
16-Apr-03	1	0	2958	1931
F71	VHF Aerial	2	13/2/2006	13-Feb-06	6-Feb-06
1	0	2965	2958
F71	VHF Aerial	2	19/2/2006	19-Feb-06
13-Feb-06	1	0	2971	2965


Hugh S Robinson Ph.D.
Postdoctoral Researcher
Wildlife Biology Program
College of Forestry and Conservation
University of Montana
Missoula, MT 59802
(406) 243-4128


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