As the Olympics open on Friday, we all know that a competitor from China stands a better chance of taking a medal than an athlete from Chad, but how about a model that quantifies those assumptions, providing detailed national rankings even before the games begin?

US economics professor Dan Johnson, who has ranked Olympic nations from 1 to 130, told Philippa Thomas that his original model of prediction, which he claims is 97% accurate, looked at whether there are things that a nation might have or lack that would serve as good predictors of Olympic medal success and "that wouldn't involve us knowing anything about the athletes themselves".

Get in touch with Today via email , Twitter or Facebook or text us on 84844.