Item analysis and validation
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The document discusses the process of developing and validating test items which includes a try-out phase, item analysis phase, and item revision phase. Key aspects of item analysis are calculating the item difficulty index and discrimination index to evaluate how well each item measures the intended construct and distinguishes between students with high and low ability levels. Formulas and interpretation guidelines are provided to help determine whether items should be retained, revised, or discarded based on these analysis results.
Item analysis and validation
- 2. The teacher normally prepares a draft of the test. Such a draft is subjected to item analysis and validation to ensure that the final version of the test would be useful and functional.
- 3. Try-out phase Item analysis phase Item revision phase
- 4. Item Difficulty Discrimination Index
- 5. defined as the number of students who are able to answer the item correctly divided by the total number of students.
- 6. Item = Difficulty # of students w/ correct answer total number of students
- 7. What is the item difficulty index of an item if 25 students are unable to answer it correctly while 75 answered it correctly?
- 8. Range of difficulty index Interpretation Action 0 – 0.25 Difficult Revise or discard 0.26 – 0.75 Right difficulty retain 0.76 - above Easy Revise or discard
- 9. tend to discriminate between those who know and those who does not know the answer. cannot discriminate between those two groups of students.
- 10. An easy way to derive such a measure is to measure how difficult an item is with respect to those in the upper 25% of the class and how difficult it is with respect to those in the lower 25% of the class.
- 11. Index Of Discrimination = DU-DL
- 12. Obtain the index of discrimination of an item if the upper 25% of the class had a difficulty index of 0.60 while the lower 25% of the class had a difficulty index of 0.20.
- 13. The index of discrimination can range from -1.0 (when DU =0 and DL = 1) to 1.0 (when DU = 1 and DL = 0).
- 14. Index Range Interpretation Action -1.0 to -.50 Can discriminate but the item is questionable Discarded -.55 to .45 Non-discriminating Revised .46 to 1.0 Discriminating item Include
- 15. Item Options 1 A B* C D 0 40 20 20 Total 0 15 5 0 *The correct response is B. Upper 25% 0 5 10 5 Lower 25%
- 16. Item Difficulty = # of students w/ correct answer total number of students = 40 100 = 40% (within of a “good item”)