[Hint: D = (Up - LP)/U, and p = (Up + LP)/(U + L). Consequently, since the value of Up can never be greater than U, when D = 1.00, Up = U and LP = 0.)
When the number of examinees in the upper and lower groups are equal and the item discrimination index (D) equals 1.00, the item difficulty index (p) must be equal to
A) .00.
B) .50.
C) .75.
D) 1.00.

Question

Quizplus · Accepted Answer

Given D = 1.00, Up = U and LP = 0, and the formula for p = (Up + LP)/(U + L), substituting the values gives p = (U + 0)/(U + U) = U/(2U) = 1/2 = .50.

[Hint: D = (Up - LP)/U, and P = (Up