Messages

1

Questions and Answers / Re: Differential Item Functioning

« on: November 08, 2013, 11:28:08 AM »

Hi Eveline,

thank you for your response, it helped me a lot!

I read about the Wald test (Lord 1980) – is it correct that the Wald test is applied to include the difficulty parameter as well as the discrimination parameter in testing for DIF? That would mean that the estimated model (item – dif.variable + item*dif.variable) is a 2PL model, right? In that way the model would be appropriate to detect non-uniform DIF of an item?!

Thanks and best wishes,
Katharina

2

Questions and Answers / Differential Item Functioning

« on: October 30, 2013, 03:53:25 PM »

Hi,


I am calculating DIF analyses with dichotomous items from TIMSS comparing two German versions of the test to identify a set of anchor items for further research.
The manual describes quite well how to formulate the model statement and how to interpret the output, but due to the fact that I am writing a statistics thesis I am furthermore interested in details about the applied mathematical models and test statistics.

Concretely, I would be glad to get some reference papers to

a)   the underlying assumptions and model specifications when computing “model item – dif.variable + item*dif.variable”
b)   the computed “Chi-square test of parameter equality” (e.g., ConQuest Manual, Figure 8-2)
c)   test specifications for the ESTIMATE values for the item*dif.variable term (ConQuest Manual, Figure 8-2, TERM 3)
[Of special interest would be a reference proving that “If zero is not element of [ESTIMATE – 2*ERROR; ESTIMATE + 2*ERROR] it is an indicator for the existence of DIF”.]


Thanks and best wishes,
Katharina