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As forms for New Zealand's March 5 census start being delivered to homes today it is timely to consider whether there are cheaper, more effective, ways for the country to get the population data it needs.
This will be the most expensive census conducted in New Zealand so far, with a budget of $90 million, up from $78 million in 2006.
Even the scheduled 2011 census, which was cancelled because of the Christchurch earthquake, cost $65 million.
Although no data was collected there were significant costs which needed to be met, such as paying more than 7000 contractors who had already delivered census forms to about 500,000 houses.
With the cost of running a census getting more expensive, some argue the frequency of New Zealand's five-yearly operation should be reduced to once every 10 years, as it is in the United States.
Others have considered whether a population register – as is common in Scandinavian countries – should take the place of the census, potentially saving money in the long term.
What is clear is that New Zealand needs quality population data.
Census information not only provides a snapshot of who lives where, but helps determine school decile ratings and government funding for things such as district health boards, and helps businesses plan for the future.
While the cost of running a census isn't cheap – $90 million over five years – the value of the data it collects is potentially worth a lot more.
Statistics NZ's principal population statistician, Christine Bycroft, says there are direct financial benefits of census information.
The health, education, welfare and transports budgets – estimated to total $150 billion between 2006 and 2011 – are all allocated using population-based funding formulas.
"The impact of poor quality population figures on major public spending could be much larger than the cost of running the census," Ms Bycroft says in her paper 'A register-based census: what is the potential for New Zealand?'.
She says some may think the census is efficient and provides value for money, but it is still a major cost and it is necessary to examine the alternatives.
Reducing the frequency
One option to save money is to run the census once every 10 years instead of five-yearly.
New Zealand has held its census every five years for more than a century, largely due to the historically high rate of migrants flowing in and out of the country.
The 2006 census found 23% of people usually living in New Zealand were born overseas.
Internal migration is also high, with half the population moving address between the 2001 and 2006 censuses.
Australia, Canada and Ireland, all countries with comparably high levels of external migration, also conduct five-yearly censuses.
Many countries, however, conduct a census every 10 years. The UK has done this for more than 200 years.
Auckland University statistics Professor Thomas Lumley says the US also conducts its census once a decade, with a mandatory survey of 2% of the population each year.
He says that annual survey does a good job of keeping the census data up to date.
Not necessarily much cheaper
However, halving the frequency of the census does not mean the cost will also be halved.
Dr Lumley says having a 10-yearly census means the data will become less accurate, so a survey would need to be conducted inbetween censuses, as is done in the US.
"Also, if you only run it every 10 years there's an awful lot of setting up and training of new staff to do.
"In the US, for example, a large number of the census bureau's employees who were working on the current census will be eligible for retirement before the next census.
"That sort of thing means there are extra costs, so reducing the frequency wouldn't save half the cost of a census."
Dr Lumley says following the US model may be a good option for New Zealand, but there would need to be proof of significant cost savings to justify it.
A population register
Some countries, mainly in Europe, have done away with the nationwide census survey and instead use administrative data to obtain the data.
Sweden, Denmark, Norway and Finland have used administrative population registers as the source of population estimates since the 1970s.
The Netherlands, Germany, Belgium, Austria, Solvenia, Israel and Singapore have also fully or partly replaced their traditional censuses with a population register.
The register includes basic demographic information such as date of birth and sex, and people are recorded at their home address.
An address register is a major part of the system, and "other registers are linked to the population register and replace census information for variables such as income, employment status, and education qualifications", Ms Bycroft says.
Any gaps in the information obtained from the registers can be filled in by doing periodic surveys, but overall, the registers eliminate the need for a nationwide census survey.
Wouldn't fly in New Zealand
Population registers have a long history in parts of Europe – Ms Bycroft says the modern registers may have grown out of much older village or parish registers, as in Finland.
But Dr Lumley says this would not be well received here.
"People in the English-speaking world have traditionally not liked having that sort of detailed government monitoring of everything.
"Whereas people in parts of Europe have been happier with it. It's also not cheap to set up that sort of system."
Ms Bycroft says a system of linked registers to provide census-type information only works in countries which already have a population register.
She says such a system would be expensive and would require a huge increase in data shared between government agencies, which the public would likely object to.
"Public acceptability is a major factor, and statistical benefits may not feature heavily in any debate.
"If the New Zealand government wished to move in this direction in the longer term, the essential base population register would still be expensive to create and perhaps more importantly, to maintain.
"It would need to be justified by major improvements in government efficiency, or some other purpose such as secure and compulsory identification."
Flaws in the current system
One person with views on the confidentialty of the census is NBR ONLINE chief reporter Jock Anderson.