Cohabitation a sign of inability to commit?

My SO and I have some challenges in our relationship and I although the relationship is great, I sometimes wonder if we will be together forever or how we compare to other couples. Anyway I found this quiz that measures the possible longevity of your relationship. One of the assumptions the test makes is that if you’re living together, it counts against your relationship longevity because either one or both of you have a problem committing. They went on further to say that marriage is a sign of increased relationship longevity. I did the quiz twice; once with “living together” as our relationship status and once with “married”. Our longevity went from 76% to 93%, with that one change. I thought this was interesting since so many people believe that marriage is just a piece of paper.

Yes I’m aware that these quizzes arent an accurate measurement for your relationship and that each relationship is different. My post is simply to see what opinions others have on this subject.