The essence of my previous post was that the 2013 Census usually resident population count was lower than Stats NZ’s estimated population count by around 230,000. That seemed to me to be quite a substantial difference, but there are a number of reasons for this:
- As Thomas Lumley at StatsChat pointed out, the estimate and the Census cover slightly different populations. The estimated population count is for all those who live in New Zealand, including those on overseas trips (holidays, business trips, etc). The Census usually resident population count includes all those who live in New Zealand and are present in New Zealand on Census night (ie, it excludes people who completed the form on Census night who usually live outside New Zealand, as well as New Zealand residents who just happened to be out of the country on Census night).
- According to Stats NZ, around 205,000 NZers took trips overseas in August 2013. According to MED the average trip takes around 20 days (credit given again to Thomas Lumley for pointing me to these stats). Thomas suggests temporarily overseas NZ residents may account for around half of the difference between the Stats NZ estimate and 2013 Census count. This leaves around 115,000.
- I’ve been in touch with Stats NZ. They carry out a post-enumeration survey to check the accuracy of coverage and response to each census. The results for the 2013 Census will be available in March 2014. However the 2006 post-enumeration survey estimated that the 2006 Census undercounted by around 2%. If the same is true in 2013, then this would be an undercount of around
84,840 people(correction for bad math) 86,570 people.
Next I plan to look at Stats NZ’s sub-national population projections, and to compare those to Census counts. Those projections are even more complex, so it’ll be interesting to see how they stack up.