EDMS 623 IRT Estimation/Calibration
What we need to do the estimation/calibration?
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Examinees’ item response data (examinee by item matrix)
Computer Estimation Program (e.g., Parscale, Bilog_MG, Multilog, WinStep, etc)
Estimation Code (command file; syntax)
What we get from the estimation/calibration?
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Item parameter estimates (difficulty, discrimination, and guessing)
Person parameter estimates (latent ability scores)
Plots like ICC, Item Information, Item SE, Test Information, and Test SE.
In Parscale…
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Phase 0 reads data into the computer program;
Phase 1 computes the item statistics for Classical Test Theory;
Phase 2 estimates the IRT item parameters;
Phase 3 estimates the IRT person parameters.
Instructions for Homework
1. Download Examinees Item Response Data.txt at http://www.marces.org/EDMS623/ and
save to your computer. You may want to rename it as EDMS623.txt
2. Copy the 3PL code from next page and save it as 3PL.PSL command file. Note it should
be saved in the same location as the EDMS623.txt file.
3. Run this 3PL.PSL command file (e.g., Run All).
4. Copy and paste the following outputs into your homework:
 the estimated item parameters from Phase 2 output
 item characteristic curves (ICC) in a matrix
 the test characteristic curve (TCC)
 the histogram of estimated examinees’ ability
PARSCALE command file (.PSL) : sample codes for IRT calibrations
3PL
>COMMENTS
>FILE
DFNAME='EDMS623.txt', SAVE ;
>SAVE
PARM='EDMS623.PAR', SCORE='EDMS623.SCO' ;
>INPUT NIDCH=8, NTOTAL=33, NTEST=1, LENGTH=33;
(8A1,2X,33A1)
>TEST1 TNAME=SOCSCI, ITEM=(1(1)33), NBLOCK=33;
>BLOCKS BNAME=(MC01,MC02,MC03,MC04,MC05,MC06,MC07,MC08,MC09,MC10,MC11,MC12,
MC13,MC14,MC15,MC16,MC17,MC18,MC19,MC20,MC21,MC22,MC23,MC24,MC25,
MC26,MC27,MC28,MC29,MC30,MC31,MC32,MC33),
NITEMS=1, NCAT=2, ORIGINAL=(0,1), MODIFIED=(1,2),
REPEAT=33, GUESSING=(2,ESTIMATE) ;
>CALIB LOGISTIC, NQPTS=15, CYCLE=(50,1,1,1,1), NEWTON=2,
CRIT=0.01, SPRIOR, GPRIOR ;
>SCORE EAP, SMEAN=0.0, SSD=1.0, NAME=SOCSCI ;
2PL
>COMMENTS
>FILE
DFNAME='EDMS623.txt', SAVE ;
>SAVE
PARM='EDMS623.PAR', SCORE='EDMS623.SCO' ;
>INPUT NIDCH=8, NTOTAL=33, NTEST=1, LENGTH=33;
(8A1,2X,33A1)
>TEST1 TNAME=SOCSCI, ITEM=(1(1)33), NBLOCK=33;
>BLOCKS BNAME=(MC01,MC02,MC03,MC04,MC05,MC06,MC07,MC08,MC09,MC10,MC11,MC12,
MC13,MC14,MC15,MC16,MC17,MC18,MC19,MC20,MC21,MC22,MC23,MC24,MC25,
MC26,MC27,MC28,MC29,MC30,MC31,MC32,MC33),
NITEMS=1, NCAT=2, ORIGINAL=(0,1), MODIFIED=(1,2),
REPEAT=33, GUESSING=(2,FIX) ;
>CALIB LOGISTIC, NQPTS=15, CYCLE=(50,1,1,1,1), NEWTON=2,
CRIT=0.01, SPRIOR, GPRIOR ;
>SCORE EAP, SMEAN=0.0, SSD=1.0, NAME=SOCSCI ;
1PL
>COMMENTS
>FILE
DFNAME='EDMS623.txt', SAVE ;
>SAVE
PARM='EDMS623.PAR', SCORE='EDMS623.SCO' ;
>INPUT NIDCH=8, NTOTAL=33, NTEST=1, LENGTH=33;
(8A1,2X,33A1)
>TEST1 TNAME=SOCSCI, ITEM=(1(1)33), NBLOCK=33;
>BLOCKS BNAME=(MC01,MC02,MC03,MC04,MC05,MC06,MC07,MC08,MC09,MC10,MC11,MC12,
MC13,MC14,MC15,MC16,MC17,MC18,MC19,MC20,MC21,MC22,MC23,MC24,MC25,
MC26,MC27,MC28,MC29,MC30,MC31,MC32,MC33),
NITEMS=1, NCAT=2, ORIGINAL=(0,1), MODIFIED=(1,2),
REPEAT=33,GUESSING=(2,FIX);
>CALIB LOGISTIC, NQPTS=15, CYCLE=(50,1,1,1,1), NEWTON=2,
CRIT=0.01, SPRIOR, GPRIOR, CSLOPE ;
>SCORE EAP, SMEAN=0.0, SSD=1.0, NAME=SOCSCI ;