A negative discrimination index is a significant red flag in item analysis, meaning that more low achievers answered correctly than high achievers. The discrimination index is designed to show how well an item differentiates between students who have a strong understanding of the material (high achievers) and those who do not (low achievers), based on their overall test performance.
When the index is negative, it indicates a counterintuitive and undesirable outcome: students who scored poorly on the entire test were more successful on that particular item than students who scored well. This suggests a serious flaw with the item. Possible reasons include: the item is poorly worded or confusing to high achievers, it contains an accidental clue that low achievers picked up on, or it is measuring something entirely different from the rest of the test. Items with a negative discrimination index should be carefully reviewed, revised, or removed from the test to improve its quality and ensure it accurately assesses student learning.