When installing a new toilet paper roll in most of the hangers you have to possible schemas: the paper hangs over (in front of the roll - B) or under (behind the roll - A). toilet_paper_dilemma (copy).jpg
Is a very old debate, the discussion goes on much before the availability of the WWW, nowaday if look in Google you may find hundreds of documents about.
If we look at the problem from the point of view of usability the answer to the question “which choice is better” has a very common ergonomics answer: “it depends”.
Some survey indicates that something like 70% of people thinks that B is better, but no one, as far as I have found around has considered which is the most important factor to take into consideration.
From the geometrical point of view over solution (B) is OK, under solution (A) could be OK only if the distance d from the paper and the wall is enough to make easy for the fingers of user to pass and get easily the paper.
In this case B is for sure much better than A:
Living with a cat (some friends told me that the same proble arises also with small childrens) may change considerations in favor of under (A) solution because makes more difficult for the cat to unfold the paper:
So as happens most of the time speaking about usability there is no easy and general answer to most of questions: IT DEPENDS!