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4. Write Subscales to Separate Files
All IRT models discussed in this tutorial are unidimensional. The SPSS data file
contains two personality scales, which are relatively uncorrelated, so the files should
be calibrated seperately.
To write the files in the ASCII format required by BILOG or MULTILOG, use the following
syntax.
SPSS Syntax:
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*Select calibration data.
GET
FILE='C:\IRTtutorial\raw_reversed.SAV'.
EXECUTE .
FILTER OFF.
USE ALL.
SELECT IF(split =1).
EXECUTE .
*Writeout calibration files with no spaces between entrees.
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 .
*Writeout validation files with no spaces between entrees.
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.
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If you ran the syntax above, SPSS would have created the files below.
You may download these files for comparison.
*The data was split into agr1 and con1 for polytomous models and agr2 and con2 for dichotomous models.
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