Hi, Nathan!

Thank you so much for your suggestion! In our case, we cannot use the negative values for the wrong answer choice as this would produce inaccurate results for our grading method. 

Using the example listed in the original post above, if we put the incorrect choice at a value of -33.3%, this would correct the issue of students selecting all answer choices, but it would cause another issue if the student does not select all the answer choices. If a student selects only 1 correct answer and the 1 wrong answer, the two values would cancel each other out for the student to receive a score of 0. We also cannot use the -25% value for the incorrect choice as this would still produce an inaccurate value of points for the question (8.3%).

Any other thoughts or suggestions would be greatly appreciated! Thanks!