To calculate scores for Multiple Answers quiz questions, Canvas divides the total points possible by the amount of correct answers for that question. This amount is awarded for every correct answer selected and deducted for every incorrect answer selected. No points are awarded or deducted for correct or incorrect answers that are not selected.
For example, an instructor may create a Multiple Answer quiz question with 9 points possible that includes three correct choices and two incorrect choices. If a student selects two correct answers and one incorrect answer, they would be awarded 3 total points for that question. This would be calculated by awarding 3 points (9 total points divided by 3 correct answers) for each correct answer and subtracting 3 points for the incorrect answer.
Multiple Answer quiz questions can be regraded manually by an instructor. The Canvas document "How do I regrade a Multiple Answer quiz question?" provides instructions for this process.
At this time it is not possible to manually change the Multiple Answer grading algorithm.