"Again, couldn't it just be that the kinds of people who notice that Visa sponsors things are the kinds of people who already like Visa?"
Could be, but it's highly unlikely that a company who does surveys as its core business doesn't know this and tries to control for it, or at least explain it in they methodology section of the report they deliver.
Could be, but it's highly unlikely that a company who does surveys as its core business doesn't know this and tries to control for it, or at least explain it in they methodology section of the report they deliver.