There has been research done on this. I'm the guy here at the table who actually does surveys every day and deals with this in 25 countries. I can tell you that these are problems we confront all the time.
The most recent research on the issue of non-response is that actually the more strenuous you make the need to respond, the less reliable the data are. You can check the Pew foundation. They've done this research.
I'm a little concerned that Canada only has 21,000 Jedi whereas in the U.K. they have 390,000 who claimed that on their census forms.