Dear Michael,
I do not actually know whether a Stata routine is available for random
selecting matched controls (MCs).
I have tried to replicate your research track in Comp1.dta (please see Stata
commands below, concerning your ID 1 patient). I suppose you have to set up
a separate data set (Comp2.dta) for controls (i.e., tx==0) and invoke the
next steps of the procedure each time you need to select two random MCs.
I do hope that some Stata guru on the list can provide you with a more
efficient trick to work around this hurdle.
--------------- begin example----------------------------
save "C:\Comp1.dta"
save "C:\Comp2.dta"
use "C:\Comp2.dta", clear
drop if tx==1
(2 observations deleted)
drop if _t<=.4
(1 observation deleted)
sample 2 if _t>=.4, count
--------------- end example----------------------------
Kind Regards and I reciprocate All the Best for the current Season's
Holidays,
Carlo
-----Messaggio originale-----
Da: [email protected]
[mailto:[email protected]] Per conto di Michael McCulloch
Inviato: luned� 24 dicembre 2007 20.12
A: Statalist
Oggetto: st: selecting random matched controls: survival
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
[email protected]
www.pinestreetfoundation.org
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