Reflection on performance of multiple choice questions in exams

For four-choiced question, if the error rate is around 75%, it indicates that the 4 choices are randomly selected. On the other hand, an error rate over 90% indicates that a wrong choice was preferred by most exam-takers.

So, around 75% error rate indicates that exam-takers are basically clueless, whereas over 90% error rate indicate a mis-understanding.