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st: SV: Case-control matching_seek for help
From
"Jesper Lindhardsen" <[email protected]>
To
<[email protected]>
Subject
st: SV: Case-control matching_seek for help
Date
Tue, 5 Apr 2011 08:49:50 +0200
Hi Wu,
I think I would look into some of the programs written for this purpose AND are also documented; for example
-CEM-
-vmatch-
(use -findit- to install)
Also, if matching are to be exact(ie sex birthyear ect), you could use a "merging" strategy instead.
However, the problem with insufficient controls means that ypu would either accept it or use controls more than once - I am not sure how to do this, but you could make a 'fake' stset and then use the stata command -sttocc-
HTH,
Jesper
-----Oprindelig meddelelse-----
Fra: [email protected] [mailto:[email protected]] På vegne af Wu Yi
Sendt: 4. april 2011 15:15
Til: [email protected]
Emne: st: Case-control matching_seek for help
Hi,
I am a research assistant in the Department of Public Health, National University of Singapore. I want to do a case-control matching.
I found the following program by Stefan Kuhle using Google search.
However, the program does not work if there are not enough matching controls. It just goes to a dead loop and never exits.
Any suggestions to solve the problem? Many thanks in advance.
Best regards,
Wu Yi
*---------------------------------------------------------------------------
* Case-control matching
*---------------------------------------------------------------------------
(C) Stefan Kuhle, University of Alberta, 2007
E-mail: myfirstname.mylastname at ualberta.ca
/*
----------------------------------------------------------------------------
This syntax will perform a 1:2 case-control matching on one matching
variable.
If you want to do a 1:1 or 1:3 etc matching, please change
the while-loop condition below as indicated.
If you want to match on two
or more variables, then please uncomment the statement
'& matchvar2[`i'] == matchvar2[`rndobs']'
in the while-loop. To match on three or more variables, append more of above
statements (using matchvar3, matchvar4, etc) to the if..then condition.
----------------------------------------------------------------------------
You will need the following variables in your dataset:
**matchvar**
Variable on which cases and controls are matched. For obvious reasons,
this variable should be binary or categorical.
**case**
Binary variable that specifies if the observation is a case (=1) or a
potential control (=0).
**id**
Unique observation ID
----------------------------------------------------------------------------
*/
gsort - case id
gen match = _n if case == 1
replace match = 99999 if match == .
quietly count if case == 1
local casecount r(N)
local matched `casecount'
local total _N
local i 1
set seed 65979
quietly while `i' <= `casecount' {
local assigned 0
while `assigned' < 2 { /* If you want to do a 1:1 match, change this number to 1 (or to 3 for a 1:3 match etc) */
local rndobs = `matched' + int(uniform() * (`total' - `matched')) + 1
/* Un-comment inserted statement below to match on two variables */
/* Add more statements to match on three or more variables */
if matchvar[`i'] == matchvar[`rndobs'] /* & matchvar2[`i'] == matchvar2[`rndobs'] */ & match[`rndobs'] == 99999 {
replace match = `i' in `rndobs'
local matched = `matched' + 1
gsort - case match id
local assigned = `assigned' + 1
}
}
local i = `i' + 1
}
drop if match == 99999 /* This will drop all unmatched observations */
tab case matchvar /* There should now be exactly twice as many controls as cases */
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/