How can tennis star Roger Federer have won only 54% of the points he played, but been the best player in the world? Jeff Sackmann, the tennis stats brain behind tennisabstract.com, explains to Tim Harford how probability works in the sport.Presenter: Tim Harford Producer: Debbie Richford Series producer: Tom Colls Production co-ordinator: Brenda Brown Sound Mix: Nigel Appleton Editor: Richard Vadon