FAA Fundamentals of Instructing (FOI)Assessment and CritiqueMedium
A ground instructor reviews item statistics from a 50-question stage exam taken by 40 students. Item #22 was answered correctly by only 6 students. What is the difficulty index for item #22, and what does it suggest?
- A0.85; the item is too easy and should be revised
- B6.00; the item has excellent discrimination
- C0.15; the item is very difficult and may need review for clarity or coverage
- D0.15; the item is functioning perfectly and requires no changes
Show answer & explanationAnswer & explanation
Correct answer: C. 0.15; the item is very difficult and may need review for clarity or coverage
Difficulty index equals the number of correct responses divided by total test takers: 6 ÷ 40 = 0.15, meaning only 15% answered correctly. Such a low value indicates the item is very difficult, possibly due to poor wording, insufficient instruction, or miskeying, and warrants review.
Why the other options are wrong
- A. 0.85 would represent an easy item, but the math here yields 0.15, not 0.85.
- B. Difficulty index is expressed as a proportion between 0 and 1, not as a raw count like 6.00.
- D. A very low difficulty index signals a potential problem, not a well-functioning item.
Item Difficulty Index
A test statistic equal to the proportion of examinees who answered an item correctly, used to evaluate whether an item is appropriately challenging.
- Formula: correct responses ÷ total test takers
- Values near 0 = very hard; values near 1 = very easy
- Extreme values often prompt item review or revision
Memory trick: Difficulty index = 'how many got it right, out of everyone.'