How to measure the difficulty of a question

1. What is the difficulty index?
2. Which formula is used to verify discrimination of questions?

What is the difficulty index?

Index of Difficulty: This is the percentage of the total group which has responded incorrectly to the item (including omissions). Index of Discrimination:This is the difference between the percent of correct responses in the upper group and the percent of correct responses in the lower group.

Which formula is used to verify discrimination of questions?

Calculation: Discrimination values are calculated with the Pearson correlation coefficient, X represents the scores of each student on a question and Y represents the scores of each student on the test. Difficulty: The percentage of students who answered the question correctly.