The census: Don't count it out EVERY ten years since 1801 the British government has conducted a census, counting every man, woman and child. Is this elaborate and costly exercise still necessary? The most recent census, conducted in 2011, cost £480m ($770m) - a 35% increase in real terms over the 2001 census. On September 23rd the Office for National Statistics (ONS) began a three-month public consultation to evaluate two new ways to count the population. Unlike surveys based on random sampling, the census provides extremely accurate and fine-grained data. Researchers can look up the results for a single street. Counting everybody is also the most reliable way to determine the size of the total population: the 2011 census revealed that there were 500,000 more people in England and Wales than statisticians had thought. But this accuracy is expensive and short-lived. The ONS proposes two alternatives. The first option is to conduct the census as normal every ten years, but to collect the bulk of responses online. When the ONS offered the option to respond online in 2011, 16% of households took it up. This would preserve the detail and accuracy of the traditional census, and at £625m would cost less than another paper-based census (estimated to cost £800m). But the information gathered would still go out of date just as quickly. The second option is to use data the government already gathers in its administration of the health service, schools and so on. The ONS could use this to create an anonymised register of the population, which would be supplemented by a smaller survey of several hundred thousand people to gather information on race and religion. The result would be less fine-grained than the census, but it would be refreshed annually and, at a cost of £460m over ten years, would be a lot cheaper. Both options have been tried elsewhere. Canada, which conducts a census every five years, has offered the choice between online or paper since 2006. In 2011, 54% of people responded online. Denmark last sent out a questionnaire in 1970 and now uses a population register, as does Germany - though in 2011 it added a survey of one-third of the population. It found that there were roughly 1.5m fewer people in the country than expected. Migrants had left the country without the authorities realising. Britain's government is more relaxed about tracking its citizens than Germany's (there is no national identity card), so using administrative records would be even less precise. John Pullinger, president of the Royal Statistical Society, reckons a register would struggle to match even an out-of-date census for accuracy. Given that population figures are used to allocate vast sums of government spending, the ONS can probably be counted on to pick option one.