On the incoming side, it counts people who declare on their arrival cards that they have lived outside New Zealand for at least the past 12 months and intend to live in New Zealand for at least the next 12.
That, of course, includes returning New Zealanders. The equivalent definition on the departures side is similarly nationality-neutral.
In the latest year there was a net loss of 5800 New Zealand citizens, compared with an average net loss of 26,600 a year over the previous 10 years, and 13,200 in the year to May 2014. Harder times across the Tasman explain a lot of that.
Meanwhile, there was a net gain of 63,000 non-New Zealanders, which compares with an average 37,300 over the previous 10 years and was 14,000 more than the year before.
So who are the immigrants Peters is keen to scapegoat?
A breakdown of visa types gives us a clue. Of the 80,000 visas issued in the past year, 35,100 - 44 per cent - were work visas. That is 13,800, or 65 per cent, more than four years ago, before the need to rebuild our second-largest city boosted demand for people in the building trades. By all accounts Auckland could do with some of them too.
Immigration boosts both the demand and supply sides of the economy and historically the pattern has been for it to have an immediate impact on demand, but lift supply only with a lag. This time the composition of the migrant flow is benefiting the supply side faster, or so the Reserve Bank believes.
It is one of the reasons labour force growth has kept pace with strong employment growth, keeping wage inflation low, enabling the bank to cut interest rates and the kiwi dollar to fall.
And even though the net migration flow so far shows no sign of obediently following forecasters' predictions that it will decline sharply this year, market economists do not expect that to stand in the way of further easing of monetary policy.
It is true that Auckland's net gain of 26,600 migrants in the past year boosted demand for housing in the city.
But if you are talking about home ownership, as Peters is, there are a lot more factors at play than excess demand for roofs over heads, including distortions in the tax system and regulatory curbs on bank lending.
The New Zealand First leader also targeted foreign students, or at least the policy decision to allow them to seek employment.
Student visas are the second-largest category, representing 32 per cent of all visas issued in the past year. The total of 25,600 issued in the past year is up from 17,600 in the previous year and 9500 10 years ago.
"Indian student arrivals of 12,100 are double the previous year and Chinese student arrivals were up 22 per cent to over 7000 in the past year," Peters said.
Whatever his source for these numbers was, it was not Statistics NZ, which put the number of student visas issued to Indians at 10,100 and to Chinese at 4800.
"Young Kiwi workers are also missing out on low-skilled jobs as foreign students, most of whom want permanent residence, take over in supermarkets, service stations and hotels," Peters said. "Why should foreign students be allowed to work at all? Our supposed export education industry is supposed to be bringing in foreign exchange."
Well, it is. A report by Infometrics on the economic impact of the international education industry estimates that gross spending, including tuition fees, rose 10.4 per cent last year to $2.75 billion, the majority of it in Auckland.
"About 14,500 full-time-equivalent jobs are directly attributable to international education delivered within New Zealand, with another 15,700 jobs being indirectly supported through the industry's upstream and downstream multiplier effects," it said.
Officials' advice from 2012 about extending foreign students' rights to work argued that it was about maintaining the international competitiveness of the sector.
If "young Kiwi workers are missing out on low-skilled jobs", as Peters contends, that may have more to do with shifting patterns of demand for labour than competition from foreign students.
The Ministry of Business, Innovation and Employment's forecast for employment over the next three years expects about 28 per cent of the employment growth to be for lower-skilled workers, even though they make up about 47 per cent of all workers.
The net flow of migrants is volatile. Four years ago, for example, there was a net annual loss of 3600 compared with the gain of 57,800 in the latest year. This volatility blows the economic cycle around.
So would it make sense for policymakers to try to manage the aggregate numbers to dampen that volatility?
Probably not. As far as visa issuance goes, there are inevitably considerable time lags before people arrive. Official decisions to adjust the total up or down on cyclical grounds would be made on the basis of forecasts that are inevitably wrong. A year ago the Reserve Bank, for example, was forecasting the net migration gain in the year just ended to be half what it has turned out to be.
The bottom line is that a quarter of New Zealand's population were born somewhere else but over a period like 10 years, immigration barely exceeds emigration.
And the other three-quarters, of course, are descended from people who arrived from somewhere else, by waka, ship or plane.
Debate on this article is now closed.
