Canada recently replaced its mandatory long-form census with a voluntary survey — and now lives with the sorry results. To try to get an adequate level of response, the voluntary survey was sent to one in three Canadians instead of one in five, which increased costs. The response rate plunged anyway, from 94 percent to 68 percent. In a staggering one-fourth of Canadian communities, not enough people responded to make the data usable
More stuff I've written on the long form census scandal here.