In WINSTEPS manual for interpreting infit and outfit mean square stats. you have written that:
>2.0 Distorts or degrades the measurement system.
1.5 - 2.0 Unproductive for construction of measurement, but not degrading.
0.5 - 1.5 Productive for measurement.
<0.5 Less productive for measurement, but not degrading. May produce misleadingly good reliabilities and separations.
However, this is very different from what is practiced. Many researchers say, .70 to 1.3 for binary items and .60 to 1.4 for Likert items. And they remove items on the basis of these criteria.
Your guidelines are different. You say that values above 2 should be deleted.
Can you please explain?