/* Core code written by Raynald Levesque and */
/* Adapted for use with propensity matching by John Painter (Feb 2004)*/
/* Program developed and tested with SPSS 11.5 */
/* Procedure will find best match for each treatment case from the control cases, */
/* control case is then removed and not reconsidered for subsequent matches */
/* Order of cases is random */
/* This code is self contained in that a data file named 'population' is created for illustrative
/* purposes only.
/* For any analysis the number of Treatment cases must be specified manually */
/* and the 'Regression Modelsle' add-on module must be available  */

/* Change file path here and only here */

DEFINE !pathd() 'c:\temp\' !ENDDEFINE.

* This arrangement gives a good set of data .
* Generate sample data for illustration purposes.
SET SEED=01251701.
NEW FILE.
INPUT PROGRAM. 
LOOP id=1 TO 300.                                  /* generates 300 records              */
+ COMPUTE sex=1 + (UNIFORM(1)>.5).                 /* generates 27 treatment cases       */
+ COMPUTE age=TRUNC(50+UNIFORM(10)). 
+ COMPUTE treatm=UNIFORM(1)>.90.                   /* 1=treatment, 0=potential control   */
+ COMPUTE abc=UNIFORM(1)>.5.
+ COMPUTE def=UNIFORM(1)>.4.
+ COMPUTE hij=UNIFORM(1)>.3.
+ END CASE.
END LOOP.
END FILE.

END INPUT PROGRAM.
******************** .
* Perform logistical regression to compute propensity score (n treatment cases = 27 for original example).
******************* .
LOGISTIC REGRESSION VAR=treatm
  /METHOD=ENTER sex age abc def hij
  /CONTRAST (sex)=Indicator
  /SAVE PRED
  /CRITERIA PIN(.05) POUT(.10) ITERATE(20) CUT(.5) .
RENAME VARIABLES (PRE_1=propen) .


*********************.
* Note number of Treatment cases and place number after MACRO CALL near end ofthis program .
********************* .
FREQUENCIES
  VARIABLES=treatm
  /ORDER=  ANALYSIS .


SAVE OUTFILE=!pathd + "population.sav" .


********************* .
** End Preparation .
********************* .
GET FILE= !pathd + "population.sav".
COMPUTE x = RV.UNIFORM(1,1000000) .
SORT CASES BY treatm(D) propen x.
COMPUTE idx=$CASENUM.
SAVE OUTFILE=!pathd + "mydata.sav".

* Erase the previous temporary result file, if any.
ERASE FILE=!pathd + "results.sav".
COMPUTE key=1.
SELECT IF (1=0).
* Create an empty data file to receive results.
SAVE OUTFILE=!pathd + "results.sav".
exec.

********************************************.
* Define a macro which will do the job.
********************************************.

SET MPRINT=no.
*////////////////////////////////.
DEFINE !match (nbtreat=!TOKENS(1))
!DO !cnt=1 !TO !nbtreat

GET FILE=!pathd + "mydata.sav".
SELECT IF idx=!cnt OR treatm=0.
* Select one treatment case and all control .
DO IF $CASENUM=1.
COMPUTE #target=propen.
ELSE.
COMPUTE delta=propen-#target.
END IF.
EXECUTE.
SELECT IF ~MISSING(delta).
IF (delta<0) delta=-delta.

SORT CASES BY delta.
SELECT IF $CASENUM=1.
COMPUTE key=!cnt .
SAVE OUTFILE=!pathd + "used.sav".
ADD FILES FILE=* 
	/FILE=!pathd + "results.sav".
SAVE OUTFILE=!pathd + "results.sav".

************************************************ Match back to original and drop case  from original .
GET FILE= !pathd + "mydata.sav".
SORT CASES BY idx .
MATCH FILES 
 /FILE=*
 /IN=mydata
 /FILE=!pathd + "used.sav"
 /IN=used
 /BY idx .
SELECT IF (used = 0).
SAVE OUTFILE=!pathd + "mydata.sav"
 / DROP = used mydata key delta.
EXECUTE.
!DOEND
!ENDDEFINE.
*////////////////////////////////.

SET MPRINT=yes.

**************************.
* MACRO CALL (first insert the number of cases after nbtreat below) .
**************************.
!match nbtreat=27.

* Sort results file to allow matching.

GET FILE=!pathd + "results.sav".
SORT CASES BY key.
SAVE OUTFILE=!pathd + "results.sav".

******************.
* Match each treatment cases with the most similar non treatment case.
* To include additional variables from original file list them on the RENAME subcommand below .
******************.

GET FILE=!pathd + "mydata.sav".
MATCH FILES /FILE=*
 /FILE=!pathd + "results.sav"
 /RENAME (idx = d0) (id=id2) (propen=propen2)
  (treatm=treatm2) (key=idx)
 /BY idx
 /DROP= d0.
FORMATS delta propen propen2  (F10.8).
SAVE OUTFILE=!pathd + "mydata and results.sav".
EXECUTE.

* That's it!.