Very, very briefly, I can tell you by doing those voluntary surveys on the west side, with repeated follow-up, explanations, parent meeting groups, that I get a 50% response rate compared to 80% to 90% in other neighbourhoods, without having to do that, simply because it's voluntary.
The mere fact that the census is mandatory means people respond at a much higher rate right now, and have in the past, in those areas. It's not the fact that you're fining them or putting them in jail. The mandatory nature raises it to a different level. People understand it is their duty to fill this out, in a way that they wouldn't by having it voluntary and saying it is one's duty.
That has been our experience.