Instead of asking "Do you want to participate ..." ask one relevant question that actually has some value for you. And put one field for entering free informat

Instead of asking "Do you want to participate ..." ask one relevant question that actually has some value for you. And put one field for entering free information. If I'm in the mood, I could actually help you to develop your business/web site by providing some highly insightful information. Can't see any value in these questionnaires, since the population who answers to them must be highly biased. If you spend many hours per day on web, there's probably a dedicated section in your brains scanning for clickable [X], "No thank you", "Close" entities on the view and giving direct commands to your mouse hand.