Study shows that wining the world cup in football increases GDP by about 3%?

I’ve heard rumors of a report saying that the country that wins the world cup in football increases its GNP with 3% on average. Does anybody have the URL or the reference? I looked, but didn’t find it.

I can see how it works, though. Denmark just won against France, and it’s a major booster of national self-esteem, as was the 1992 European Championship. Who’d have thought we’d win 2-0 against the former world champions of France?