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Education QUESTION #6797
Question 1
A researcher conducting item analysis using CTT calculates item discrimination as D = (UG − LG) / n. For a 40-student class, the upper 27% group (n=11) had 9 correct and the lower 27% group (n=11) had 3 correct. What is D, and how should this item be classified?
  • D = 0.27; Poor item to be revised
  • D = 0.55; Excellent item✔️
  • D = 0.43; Good item approaching excellent
  • D = 0.82; Poor item due to extreme discrimination
Correct Answer Explanation
D = (Upper Group correct – Lower Group correct) / n per group. Upper Group: 9/11 ≈ 0.818; Lower Group: 3/11 ≈ 0.273. D = 0.818 – 0.273 = 0.545, or using the formula D = (9–3)/11 = 6/11 ≈ 0.55. A D value greater than 0.40 is classified as excellent. This item powerfully differentiates high-ability from low-ability students and should be retained in the item bank.