a) A class of 360 students took a multiple-choice examination. Each examination item had four possible answers, of which only one was correct. On the first of the items, the following number of people...

a) A class of 360 students took a multiple-choice examination. Each examination item had four possible answers, of which only one was correct. On the first of the items, the following number of people in the class marked the correct answer: Item1 = 62; Item2 = 200; Item3 = 305. Calculate the item-difficulty index for each and comment on the facility of each item.

b) On the basis of the marks on the whole examination, the class was divided into four. The top and bottom 25% of the class were extracted. The number of each of these sub-samples endorsing each of the answer choices is presented for three items. The answer with the asterisk is the correct answer. Calculate the item discrimination index for the three items and comment on whether the items should be retained or not.