After several years of study, and twenty blackboards, scientists at John Lennon's University, Liverpool, England, UK, the Earth have finally discovered the optimal length of toilet roll required to wipe any backside.
"Basically," said Professor Rosseforp, "It comes down to three factors."
Turning to a blackboard, the Professor showed the equation log: AR(5e) * Ho / e.
"You see, the radius of the backside (AR) is one element, whilst the runniness of one's business can be governed by 'e', and the length of time one has spent on the lavatory is shown by Hours over runniness (e). All of this is logged.
"For example, a large bottom, such as J-Lo's would require approximately three sheets per minute for a standard poo, whilst if she'd had a little upset in the tummy, you could quite easily treble that."
Professor Rosseforp showed the press conference J-Lo's backside and three sheets of toilet roll: "Voila!"
On asked how much toilet paper Peter Mandleson would require, Professor Rosseforp replied: "For an arse that big, you'd need two rolls!" He then produced two rolls to prove his point, and asked if he could measure people's bottoms.
It must be noted that there was no toilet paper in the university toilets. Apparently, as fast as the janitor puts one in, it vanishes.