With the endless debate in the PR community about how to best show a return on investment ("I don't know the definition of good PR, but I know it when I see it"), I've wondered how other marketing approaches calculate results.

Sponsorship in particular seems slippery. Not criticizing sponsorship - but it seems to come down to reach? Or social currency, as the writer below analyzes. This would seem to break down the investment, but not the return.

Any sponsorship experts out there with a formula showing what the dollars bring back?