I have a long-running survey with one question where participants are forced to select a single choice. Now we are discussing about changing this question to multiple selection. Is there a way to compare the numbers before and after?
A multiple choice answer loses the attribute of preference.
When I choose a single option, I eventually choose the one I prefer, even if some other options seem close. When I choose multiple answers, any one of them is a possibility, even if remote.
It makes quite a difference in the survey. I would regard it as a different question, unless you want to change the wording to account for some preference.
Hard to say more without specific details, but this is my general view.