There is a good section in the book Soccernomics about the economic impact studies that cities and countries sponsor when they are hoping to host a huge sporting event like the World Cup or the Olympics. The gist of it is that you can make an economic impact study say pretty much whatever you want, since it’s an exercise in speculation, and that the economists hired by bid committees make sure the numbers say yes.
The truth, however, is that most such events don’t provide much economic stimulus, and often turn out to be money losers. This isn’t to say that cities or countries shouldn’t try to host these events — but, as the Soccernomics authors argue, they should at least realize that what they’re doing is paying for the right to host a big party. The same is generally true for public funding of new sports arenas, as the economist Dennis Coates made clear not long ago.