[Rasch] DIF Question

Eric Wong mcwong at cuhk.edu.hk
Fri Mar 16 20:50:04 EST 2007


Dear all,

I used WINSTEP to run DIF on 12 (ordinal) unidimensionality items


DIF class specification is: DIF=@SMOKE

 

+--------------------------------------------------------------------------------------------------------------------------------------------+

| PERSON   DIF   DIF   PERSON   DIF   DIF      DIF    JOINT                MantelHanzl ITEM                                                  |

| CLASS  MEASURE S.E.  CLASS  MEASURE S.E.  CONTRAST  S.E.   t  d.f. Prob. Prob.  Size Number  Name                                     

|--------------------------------------------------------------------------------------------------------------------------------------------|

| 1         .30   .16  2         .77   .09      -.47   .18 -2.56 376 .0108 .1653  -.24      3 Had angina that affected life                  |

| 2         .77   .09  1         .30   .16       .47   .18  2.56 376 .0108 .1653   .24      3 Had angina that affected life                  |


The Mantel-Haenszel DIF has probability .1653 and size .24 logits, and 
The Winsteps-Rasch equivalent is DIF Contrast = .47 logits, probability = .0108.

Any idea why the p-values and the DIF sizes disagree?  What conclusion could I make?

Many thanks!

Eric
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