If SFILE=filename is specified, a file is output which contains the item and category information needed for anchoring structures. It has 4 heading lines (unless HLINES=N), and has the format:

 

1. The item sequence number (I6)

Only if there are multiple groupings in ISGROUPS= or SAITEM=Yes, otherwise this is omitted.

 

2. The category value (I3) (STRU) - the Rasch-Andrich threshold.

 

3. structure calibration (F7.2) (user-rescaled by USCALE=) (number of decimals by UDECIM=) (MEASURE)

If the category is an intermediate category with no observations, kept in the analysis by STKEEP=YES, then its structure calibration is shown as very large. The next higher calibration is shown as very low.

Use this for anchoring, together with IFILE=

 

If CSV=Y, these values are separated by commas. When CSV=T, the commas are replaced by tab characters.

 

SFILE=? opens a Browse window

 

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Anchoring with Unobserved Categories

 

When STKEEP=YES and there are intermediate null categories, i.e., with no observations, then the Rasch-Andrich threshold into the category is set 40 logits above the highest calibration. The Rasch-Andrich threshold out of the category, and into the next category, is set the same amount down. Thus:

 

 

This is an attempt to model unobserved categories for the next time, when they may be observed.

 

If categories will not be observed next time, then please specify STKEEP=NO, which automatically drops the category from the rating (or partial credit) scale.

 

If categories may be observed next time, then it is better to  include a dummy data record in your data file which includes an observation of the missing category, and reasonable values for all the other item responses that accord with that missing category. This one data record will have minimal impact on the rest of the analysis.