DIF and delete !item

[jarrn]

Greetings,

I am trying to calculate differential item functioning with my data (find datafile attached).

Using the following ConQuest commands everything works out right.

Code: [Select]

title Haupterhebung EM-1D (Nur HRGYBA-Studierende);
set constraints=cases, warnings=no;
datafile Haupterhebung-HRGYBA-01.dat;
format id 1-3 stgang 8 responses 9-144;
codes 0, 1;
/* delete !item(4,5,9,10,14,15,23,24,28,29,33,34,38,39,43,44,48,49,50-136); */
model item -stgang + stgang*item;
estimate;

Unfortunately I only want to include some few Items (the other ones belong to different subscales of my test).
As soon as these items get deleted with the commented out line, Conquest throws hundreds of errors at me saying

Code: [Select]

No data for stgang X, item Y estimation cannot proceed. Data is needed for a constraint.with X and Y looping through all possible stgang-deleted-Item-combinations.
This happens even if I only delete one or two items in the dataset.

Any Help? Am I missing something important?

As soon as I comment out the delete statement everythin works like a charm.

Thanks in advance,

David

[Eveline Gebhardt]

Dear David

For DIF estimation, you will need to exclude the deleted items from the format statement.

Eveline