Which of the following is defined by "the number of people who get a particular item correct" for a test that measures achievement or ability?

Correct option is A

-Item difficulty refers to the proportion of test-takers who answer a given item correctly in an achievement or ability test.
-A higher p-value (closer to 1) indicates an easier question, whereas a lower p-value (closer to 0) indicates a more difficult question.
-Ideal test items usually have a moderate difficulty level (p ≈ 0.5) to maximize discrimination between high and low performers.

Since the question defines item difficulty as "the number of people who get a particular item correct", the correct answer is Option 1: Item Difficulty.

Information Booster:
-An optimal difficulty level is around 0.4 to 0.6 in most standardized tests.
-Item difficulty is used in item analysis to refine exams and assessments.
-The Rasch Model (IRT - Item Response Theory) is an advanced method for analyzing item difficulty beyond classical test theory.
-The Distractor Analysis helps in evaluating incorrect response options to improve test quality.
-Test developers (e.g., ETS for GRE, College Board for SAT) use difficulty indices to standardize test items.