Census - The polemic of the long form

Next year is the year of the Census in Canada. The Canadian Census is conducted every 5 years and used to be composed of a long questionnaire and a short questionnaire. Both were mailed to the respondents who had to respond, since it was mandatory. While the short form were sent to every household, the long form were sent to only one fifth of the households, so it was a Survey rather than a Census.

Now they decided that the long questionnaire will be voluntary and will be sent to one third of the households. The main argument is that there are people who considers the long form particularly intrusive, with too personal questions. It had 40 pages in 2006. But this argument seemed not to be enough and the subject became a huge polemic. Concerns about results accuracy and continuity of historical trend are among the main points among those who are against a voluntary long form.

A good statistical point against the voluntary survey is that it is not only supposed to be a very accurate picture of Canadians but it is also a very important base for many other surveys, official or not. Until the results of the new Census in 2016 come along, Statistics Canada itself will be relying on the long 2011 form results as a baseline for designing and weighting their other surveys.

I have to say that I am not sure what precisely "voluntary" means in this case, in particular, what will be the effort done to get people to answer to the long form. What would the expected response rate be? It seems that Statistics Canada can get pretty good response rates even with voluntary surveys, and if that is so maybe there is no reason for concerns. We have to remember, though, that they are increasing from 1/5 to 1/3 the number of questionnaires sent, and that seems to mean they are expecting a sizable non response rate. Even with all the weighting development we have nowadays, I would think they should do a test or try to estimate somehow the non response rate, and the decision as to whether or not to go mandatory would depend on that. I think this particular Survey cannot afford to be questionable on its methodology.

Back on the time I was at the graduating school, I had a professor that said a Survey would be as accurate as a Census and cost much less. That was also back in Brazil where Censuses are not mandatory. It seems to me that it could be a Survey as long as it was mandatory or as long as it had a very high response rate. One of the arguments against the Census is that it is actually not precise at all, with lots of people not answering to it, or not telling the truth. I think the biases from this kind of thing would be really minor, much lower than the possible biases in a survey with low response rate. So I think things are not as simple as replacing censuses by surveys, there are some serious concern involved. Not to say that making people answer a survey could in fact increase non response error since we could think that people that don't want to respond could "lie" if forced to respond.

Back to the Canadian polemic, it seems possible that there are some political reasons for the changes (rather than only technical), which is of concern. Anyway, let's hope scientific concern drives the choice of the method. I am sure there are very good statistician behind this and I hope they can be heard.