Here's a breakdown of the concept:
* Definition: It is a percentage representing the number of test takers who answered a specific question correctly.
* Calculation: Difficulty index (DI) = (Number of students answering correctly) / (Total number of students)
* Range: The difficulty index ranges from 0 to 1.
* Interpretation:
* DI close to 0: The item is very difficult, and only a few students answered it correctly.
* DI close to 1: The item is very easy, and most students answered it correctly.
* DI around 0.5: The item is considered of moderate difficulty, with roughly half the students answering it correctly.
Key Uses of Difficulty Index:
* Item Analysis: To analyze the effectiveness and difficulty of individual test items.
* Test Development: To ensure a balanced difficulty level across the test and to identify items that need revision or replacement.
* Educational Planning: To guide teachers in selecting appropriate instructional materials and adapting their teaching methods.
Example:
If 50 out of 100 students answered a particular question correctly, the difficulty index for that question would be 50/100 = 0.5, indicating a moderate difficulty level.
It's important to note that:
* The difficulty index only reflects the relative difficulty of an item within a particular group of students. It does not necessarily imply the absolute difficulty of the item itself.
* Other factors, such as the content domain, time limits, and clarity of instructions, can also influence the difficulty level of an item.