OTTAWA — The U.S. Census Bureau tested out the idea of making a mandatory national survey voluntary — as the Conservative government now plans to do with the census in Canada — but quickly discarded the idea because it produced what was deemed unreliable data at an exorbitant price.

The American Community Survey was introduced in 1996 to replace the U.S. long-form census and is mandatory. Rather than being sent out every 10 years when the census is taken, it's conducted on a continuous monthly basis, sampling a total of three million households each year.

In the fall of 2002, Congress asked the Census Bureau to find out how the ACS would function if it were voluntary instead of mandatory, and tests were conducted in the spring of 2003.

The bureau saw a "dramatic decrease" in response rates when they tested out a voluntary version of the ACS, with mail-in replies dropping by about one-third. Only 22 per cent of black households and 20 per cent of Hispanic households mailed back a completed survey when it was voluntary, compared to 43 per cent of white households and 42 per cent of non-Hispanic households.

The bureau followed up by phone — a more expensive and time-consuming method — with households that didn't respond by mail, but also saw about 18 per cent less co-operation when they said the survey was voluntary.

Now, the survey remains mandatory and contains many questions similar to Canada's long-form census, including those on race, education, employment and relationships between people in the household. The survey also asks how well people speak English, when they came to live in the U.S., whether they have "serious difficulty concentrating, remembering or making decisions" because of a physical, mental or emotional condition and whether the family uses food stamps.

The survey also contains a host of detailed questions about property, including monthly utility costs and rent or mortgage payments, number of vehicles, and whether the home has hot and cold running water, a flush toilet, a refrigerator and "telephone service from which you can both make and receive calls."

Interestingly, the Census Bureau found only a small difference between the mandatory and voluntary surveys in terms of how many questions people completed.

"Although differences in respondent behaviour were found in their choice to participate in the interview, once the respondent made the choice to participate, the data provided were nearly as complete," a 2003 report on the experiment concludes.

The lower response rate by mail and phone required more in-person followup, which the bureau said is 10 times more expensive than the other methods. In the end, the bureau calculated that making the ACS voluntary would cost an additional $59.2 million U.S. each year, primarily because the sample size would need to be increased and more expensive in-person followup visits conducted to generate enough response.

Canada's voluntary National Household Survey is estimated to cost an extra $30 million over the census for similar reasons. The Conservative government announced at the end of June that it was abolishing Canada's mandatory long-form census and replacing it with a voluntary survey, a move critics have said will produce a skewed national statistical portrait.