Assume that of 55 persons who take a test, 10 of the 15 people falling in the upper group on total test score and 5 of the 15 falling in the lower group on total test score pass a given item. What is the item difficulty index?
A) .17
B) .33
C) .50
D) 1.00

Question

Quizplus · Accepted Answer

The item difficulty index is calculated by taking the average of the proportion of people passing the item in the upper and lower groups. Here, 10/15 in the upper group and 5/15 in the lower group pass the item. The average is (10/15 + 5/15) / 2 = 0.50.

Assume That of 55 Persons Who Take a Test, 10