The data is very clear... Ads work. They absolutely shouldn't almost ever, but they do. With the cornucopia of analytics available, companies have long been able to see if their ads work, and if they didn't, they would've stopped long ago. Hell even before the Internet they had ways to prove ads work.
edit: gotta say it's pretty sad that so many simpletons downvoted this. Ya know, ads working is something that I hate. I hate ads. I want them all to go away. I'm simply stating a well known fact: they absolutely work, even on people like you and I who do our best to block and ignore them.
You're pretty fragile if that fact upsets you enough to shoot the messenger.