Hi Eveline, hi guys,
I know that the topic is a bit older, but I read it a few days ago and I'm a bit unsure now.
Based on the DIF tutorial by Adams & Wu (2010) and many others (e.g. Le, 2009), I have so far assumed that DIF is the absolute difference between the two estimated difficulties of the two groups. So it should be (abs.) sum of the both group-specific values given in term 3 for item i (deviation from the average difficulty of the item i), shouldn't it?
Thus, EST/SE would only be the significance of the deviation of one group from the average difficulty of the items, while the significance of DIF in relation to the item-specific Wald-Test could be determined by Chi square = [Est(1)/SE(1)]^2 + [Est(2)/SE(2)]^2 = 2 (Est/SE)^2, df=2-1. Where EST corresponds to values in term 3, 1=Group 1 and 2=Group 2, or?
Thanks
Alex