Item Analysis and Discrimination Index (EASY TO UNDERSTAND)

Easy To Understand

Made by: Education Resource Hub

What Is Item Analysis?

Item analysis means checking your test questions to see:

·       How easy or hard each question is

·       How well each question tells who really knows their stuff from who doesn’t

Item Difficulty/Analysis

Think of a test question like a video game level:

Most people answered the question correctly when it was easy.

Few people answered it correctly when it was hard.

You count:

·       How many students got the question right?

·       Divide by how many took the test.

Example:
Imagine 20 students answer Question 1:

·       15 got it right

·      So... 15/20 = 0.75 or 75% | 15 divided by 20 is equal to 0.75 or 75%

If a lot got it right, it’s easy. If just a few got it, it’s hard.

Interpretation Table

Discrimination Index

This is about which students get the question right:

·       Do top students get it right more often than struggling students?

How to check:

1.     Line up your test scores, highest to lowest.

2.     Pick the top group (smartest) and the bottom group (needs help).

3.     For each group, count how many got the question right.

Example:

·       Upper Group 5 students: 4 got it right

·       Lower Group 5 students: 1 got it right

So:

·      Top group score: 4/5 = 0.8  (80%) | 4 divided by 5 is equal to 0.8 or 80%

·      Bottom group score:  1/5 = 0.2 (20%) | 1 divided by 5 is equal to 0.2 or 20%

Discrimination Index:
Subtract bottom from top: 0.8-0.2=0.6 | 0.8 minus 0.2 is equal to 0.6

If the number is high, that’s good! It means the question separates the “experts” from the “learners.”
If the number is low or negative, it’s a bad question—maybe confusing or tricky in the wrong way.

 Interpretation Table

Question:

• How will you know which one is the upper group and lower group / how to get the upper group and lower group:

Answer: 

Divide the scores into groups:

Take the top 27% as the upper group and the bottom 27% as the lower group.

For example, if you have 30 students, calculate 27% of 30:

30×0.27=8.130×0.27=8.1, so round to the nearest whole number, in this case, since it's.1, we won’t round it off, instead we will use 8, therefore 8 students in each group.

• Upper group: The students who scored the highest—the top 8 scores.

• Lower group: The students who scored the lowest—the bottom 8 scores.

In Summary:

·       Item difficulty: How many got it right? (Easy = high number, hard = low number)

·       Discrimination index: Did top students do better on it than struggling students? (Big difference = good question!)

 

Why do teachers use this?

To make sure tests are fair, clear, and tell who knows the material well/learned the lesson!

"A good test question is one most students can try, but only those who really understand will get it right—and that’s what item analysis checks for!" - Zephyr