Do two large glasses of wine triple your risk of mouth cancer, as claimed on a health leaflet spotted by a sceptical listener? Tim Harford examines the difficulties of extracting smoking from the equation. Surprising as this may seem, one of the world's best tennis players of all time, Roger Federer, is also the worst ranked player on one scale. The scoring system makes it possible to lose a match despite winning more points, and Federer has lost the highest percentage of these types of games. Tim speaks to sports number-cruncher Ryan Rodenberg about why this might be the case.