A pair of advertising campaigns run by Canadian province Ontario between 2003 and 2005 alerted citizens to the five warning signs of a stroke. The ROI was measurable in one sense, and priceless in another. In the first case, according to a Reuters report, there was a marked increase in ER visits to get symptoms checked out. This is critical, since the first three hours can be make or break when the most common type of stroke occurs. What cannot be calculated, other than to use the priceless descriptor, is the number of lives saved and the amount of medical expenses which are saved.
The campaign was not repeated in 2006, however, and the unsurprising result was that the number of strokes that went unrecognized and untreated during the critical window went back up. The obvious conclusion is that such an advertising campaign needs to be continuous. A health official in Ontario did mention two numbers which bear consideration. 1.8M was spent on the campaign per year, against over 800M spent treating strokes.
RBR observation: You never see Coke or McDonald's or any other global brand taking an extended holiday from advertising themselves, so there's no reason to expect it to be any different for this kind of message. So maybe we should encourage the government to take advantage of the media to promote the general welfare. The trick is to determine what kind of information has a real measurable public benefit and what kind doesn't need to be tied to a continual media drumbeat.