Suppose that 15 of the 20 examinees who score above criterion level on a criterion-referenced test get an item right, but only 3 or the 30 scoring below criterion level get the item right. What is the item?s D index?
A) .40
B) .48
C) .60
D) .65

Question

Quizplus · Accepted Answer

The D index is calculated as (a - c) / (a + b + c + d), where a is the number of examinees who score above criterion level and get the item right, b is the number of examinees who score above criterion level and get the item wrong, c is the number of examinees who score below criterion level and get the item right, and d is the number of examinees who score below criterion level and get the item wrong. In this case, a = 15, b = 5, c = 3, and d = 27. Therefore, the D index is (15 - 3) / (15 + 5 + 3 + 27) = .65.

Suppose That 15 of the 20 Examinees Who Score Above