Studies on Game Advertising Effectiveness?

I’ve spent the past few months interviewing many different people on the subject of games and advertising — professors, ad sales professionals, game developers — you name it. I’ve learned a great many things from these interviews, but one thing I have not learned is of the existence of much research on the topic of improving advertising effectiveness. I am referring specifically to ads in and around games, as well as advergames themselves.

I’ve found plenty of non-game-specific ad research. And there are several studies (sponsored by major publishers and/or in-game ad networks) that seek to prove advertisements in games are effective, without exploring what can make them more effective.

So I thought I’d ask you all: if you’re aware of any studies on the subject of game advertising effectiveness, especially studies that weren’t sponsored by organizations with a perceived bias, I’d greatly appreciate hearing about them.