Mathematicians are running the rule over the World Cup - less for the quality of the soccer than for the chance to prove an intriguing statistical quirk called the "Birthday Paradox".

Strange as it may sound, 16 of the 32 teams with 23-man squads at the tournament in Brazil have players who share a birthday, although mathematicians are far less surprised than the rest of us.

Statisticians have known for some time there is a slightly more than 50 percent chance that in any group of 23 people, two will have the same birthday.