How Effective Are PSAs?

Residents of the greater Boston area should be more than familiar with this billboard from Modernista:

Now with GOOD recently featuring the following ads in light of current congressional efforts to weaken the EPA and hollow out the Clean Air Act, we just can't help but wonder, how effective are such ads?

Well, we probably won't know the fate of the Clean Air Act until Congress finally votes, but if you want to see what Stop Handgun Violence has been able to accomplish with their campaign, click here.

Of course, no discussion about PSAs is complete without mention of the venerable Ad Council. In this day and age of emerging media, just how current and how relevant are the Council's efforts? See for yourself here.