Models

"Certainly economists build and test theories with models, often quite simplistic ones. But they do not [all] believe that the model is real. Only politicians do that.
    "So what we see in the various 'social investment' analyses being presented and will see in the many which will proliferate as this becomes the slogan du jour, is an endless set of dodgy arithmetic calculations all of which will show positive returns. Much like we see in the many past stadium or motorway or entertainment event proposals which inevitably show a major positive return to the suburb/city/country concerned. If you added all these up from the past we would live in a utopia. We do not live in a utopia."

~ Rob Campbell from his post 'Don’t be fooled by what ‘social investment’ slogan means' [addition mine]