General developer forum

What you want to do might be best done as a quiz report. You can write a new plug in to define a quiz report. And quiz reports can set up tables for their own purposes in the Moodle db.

But there would be advantages to making a special question type too. Probably you could extend the existing multiple choice question type and add bits to the question editing form to specify a category for each answer. If you make a special question type then you could back up and restore and export import this information too, which you would not be able to do from within a quiz report plug in.

Tell us more about what you mean by 'kind of mistake'?

You're aware of this report I take it, which you drill down to from the statistics report :

http://docs.moodle.org/20/en/Quiz_statistics_report#Analysis_of_individual_question_responses

Another thing to look at is STACK's concept of 'Answer note': https://github.com/maths/moodle-qtype_stack/blob/master/doc/en/Authoring/Potential_response_trees.md#answer-note-answer_note

That could be generalised to all question types. Jamie's suggestion to look at the response analysis in teh statistics is also good.