Queens
College/CUNY
Education Unit
Fall 2009
Item Difficulty - the percentage of pupils who got the item right
Item Difficulty = R/T x 100
R=the number of pupils who got the item right
T= total number of pupils who attempted the item
Item Discriminating Power is the degree to which the item discriminates between pupils with high achievement and low achievement
Item Discriminating Power = R u - R L
.................................................. 1/2T
R L = the number of pupils in the lower group (lower ten scores) who got the item right (you can also use percentages)
R U = the number of pupils in the upper group ( upper ten scores) who got the item right (you can also use percentages)
T = the total number of pupils who attempted the item