* Get raw data file (SPSS format already).
GET
  FILE='C:\IRTtutorial\raw.SAV'.
EXECUTE .


*Reverese score.
recode
c1 a1 c5 a5 c7 a7 c10 a10
(1=5) (2=4) (4=2) (5=1).
Execute.

SAVE OUTFILE='C:\IRTtutorial\raw_reversed.SAV'.
Execute.

*Dichotomize items.
    * Get reversed scored file.

GET
  FILE='C:\IRTtutorial\raw_reversed.SAV'.
EXECUTE .
  
    * Dichotomize.
recode
c1 c2 c3 c4 c5 c6 c7 c8 c9 c10 a1 a2 a3 a4 a5 a6 a7 a8 a9 a10 
(1=0) (2=0) (3=0) (4=1) (5=1).
Execute.
  
SAVE OUTFILE='C:\IRTtutorial\raw_dichot.SAV'.
Execute.

 * Write subscales to separate files, calibration and validation samples separately.
 
* Polytomous file.

GET
  FILE='C:\IRTtutorial\raw_reversed.SAV'.
EXECUTE .
 
 *Create split variable.

COMPUTE SNO = $CASENUM.
Execute.

*mark all odd numbers as 1.

IF (MOD(sno,2)) split = 1 .
EXECUTE .

*mark all even numbers as 2.
RECODE
  split  (SYSMIS=2)  .
EXECUTE .

SAVE OUTFILE='C:\IRTtutorial\raw_reversed.SAV'.
Execute.

  *Select calibration data.

GET
  FILE='C:\IRTtutorial\raw_reversed.SAV'.
EXECUTE .

FILTER OFF.
USE ALL.
SELECT IF(split =1).
EXECUTE .

WRITE OUTFILE = 'C:\IRTtutorial\con1_cal.dat'
/ id c1 c2 c3 c4 c5 c6 c7 c8 c9 c10.
Execute.

WRITE OUTFILE = 'C:\IRTtutorial\agr1_cal.dat'
/ id a1 a2 a3 a4 a5 a6 a7 a8 a9 a10.
Execute.


  *Select validation data.

GET
  FILE='C:\IRTtutorial\raw_reversed.SAV'.
EXECUTE .

FILTER OFF.
USE ALL.
SELECT IF(split =2).
EXECUTE .

WRITE OUTFILE = 'C:\IRTtutorial\con1_val.dat'
/ id c1 c2 c3 c4 c5 c6 c7 c8 c9 c10.
Execute.

WRITE OUTFILE = 'C:\IRTtutorial\agr1_val.dat'
/ id a1 a2 a3 a4 a5 a6 a7 a8 a9 a10.
Execute.

* Polytomous file.

GET
  FILE='C:\IRTtutorial\raw_dichot.SAV'.
EXECUTE .
 
 *Create split variable.

COMPUTE SNO = $CASENUM.
Execute.

*mark all odd numbers as 1.

IF (MOD(sno,2)) split = 1 .
EXECUTE .

*mark all even numbers as 2.
RECODE
  split  (SYSMIS=2)  .
EXECUTE .

SAVE OUTFILE='C:\IRTtutorial\raw_dichot.SAV'.
Execute.

  *Select calibration data.

GET
  FILE='C:\IRTtutorial\raw_dichot.SAV'.
EXECUTE .

FILTER OFF.
USE ALL.
SELECT IF(split =1).
EXECUTE .

WRITE OUTFILE = 'C:\IRTtutorial\con2_cal.dat'
/ id c1 c2 c3 c4 c5 c6 c7 c8 c9 c10.
Execute.

WRITE OUTFILE = 'C:\IRTtutorial\agr2_cal.dat'
/ id a1 a2 a3 a4 a5 a6 a7 a8 a9 a10.
Execute.


  *Select validation data.

GET
  FILE='C:\IRTtutorial\raw_dichot.SAV'.
EXECUTE .

FILTER OFF.
USE ALL.
SELECT IF(split =2).
EXECUTE .

WRITE OUTFILE = 'C:\IRTtutorial\con2_val.dat'
/ id c1 c2 c3 c4 c5 c6 c7 c8 c9 c10.
Execute.

WRITE OUTFILE = 'C:\IRTtutorial\agr2_val.dat'
/ id a1 a2 a3 a4 a5 a6 a7 a8 a9 a10.
Execute.