Rasch is a type of measurement model used in education to analyze student performance on tests. Rasch helps ensure assessments produce fair, reliable, and meaningful results. Unlike traditional scoring methods that simply count correct answers, the Rasch model creates interval-level measurements that allow for more sophisticated analysis of both student ability and item quality.
It helps create fair, meaningful scores by focusing on two things:
- Student ability
- Question difficulty
The main idea:
A student’s chance of getting a question right depends on how strong their ability is compared to how hard the question is.
Why This Matters for Assessments
Traditional Problem: When you create a 20-question test, getting 15 questions correct doesn’t necessarily mean students have 75% mastery. Some questions might be much harder than others, making the raw score misleading.
Rasch Solution: The model places both students and test items on the same measurement scale, providing more accurate ability estimates and revealing which items truly assess your learning objectives.
Why is Rasch important for educators?
- Fair comparisons: It allows you to fairly compare students even if they didn’t all get the exact same questions.
- Question quality: It identifies which questions are too easy, too hard, or not working properly.
- Growth tracking: Because scores are placed on a continuous “scale,” it’s easier to measure student growth over time.
- Focused instruction: You can pinpoint exactly where students are struggling — not just how many they got wrong, but how difficult the missed questions were.
How Rasch works (simple version):
Think of the Rasch model as creating a special ruler that measures both students and test questions using the same scale. Imagine you have a ruler where:
- Student ability is marked on one side (like measuring height in inches)
- Item difficulty is marked on the other side (using the same inch markings)
- When a student’s ability level is “higher” than an item’s difficulty level, they’re likely to answer correctly
- When an item’s difficulty exceeds a student’s current ability, they’ll probably struggle with it
This shared measurement scale is what makes Rasch analysis so powerful – you can directly compare any student to any item, or any student to any other student, even if they never took the same test items. It’s like being able to say “Sarah is taller than the doorway” and “Tom is shorter than the doorway” even if Sarah and Tom were measured with different rulers, as long as both rulers used the same inch markings.
Imagine a ruler:
- Each student has an ability level placed somewhere on the ruler.
- Each question has a difficulty level placed somewhere on the ruler.
- If a student’s ability is higher than the question’s difficulty, they are likely to get it right.
- If a student’s ability is lower than the question’s difficulty, they are likely to miss it.
Important:
Rasch isn’t just counting right and wrong — it’s looking at how hard each question is when evaluating a student’s performance.