Optimizing a Number of Overlapping Items for Eqauting Estimated Item Parameters

Many organizations that created the exam cannot estimate the amount of difficulty of item (questions). This is because if they want to estimate item base on Item Response Theory, they used an exam that finished by only one group of examinee for the standard of the difficulty of the exam; however, they cannot use only one group of examinee for estimated all exam because it leads to creating some errors e.g. fatigue, exhaustion. The approach which mitigate this problem is separate all items into several sets of items, and overlapping items in every set. According to using one group of examinee estimate item in one or more set. After that, using Linear Equating to adjust the difficulty of items in every sets into the same standard.