Do attack ads really work?

Many pundits, scribes, and scriveners alike continue to say attack ads work, and several have today suggested that Iggy went down because of the attack ads. Show me some hard evidence, please. I simply don't buy it: you have to be dumber than the proverbial door knob or Big Bobby Clobber not to see through these and any other attack ads. The Harperite base obviously enjoys them, but they're not aimed at that base. They're aimed at the undecided and opposition party voters. Who really watches these except for amusement and maybe to exclaim in mock indignation, "how naughty of them" or, from the base, how "dead on"? Or am I overestimating the average intelligence of Canadians? Perhaps.