st: selecting random matched controls: survival

[Michael McCulloch <mm@pinest.org>]

Dear Statalist members,

I would like to ask help in a routine for selecting random matched 
controls in a survival dataset.

I have patients (tx=1) and controls (tx=0), and have _stset_.
Time from diagnosis to death = _t.
In the patients, I also know the time between diagnosis and treatment 
(leadtime).

I wish to randomly select two controls per patient, from among all 
controls who have survived at least as long as the leadtime for that 
patient. For example, subject ID==1 has eligible controls:
	ID==12 | ID==13 | ID==14
Therefore, I'd like to randomly select two controls from among those 
three eligible controls.

ID	tx	_t	leadtime
1	1	1.0	0.4
2	1	1.2	0.3
11	0	0.1
12	0	0.9
13	0	1.1
14	0	0.5

May I ask how this can be done in a do-file or small program?

Happy Holidays to all,

--

Michael McCulloch
Pine Street Foundation
124 Pine St., San Anselmo, CA 94960-2674
Tel:	(415) 407-1357
Fax:	(415) 485-1065
mcculloch@pinestreetfoundation.org
www.pinestreetfoundation.org
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