Size matters
Ok, this is a bit late, but I didn’t see the poll (in a physical Sunday Star-Times) until this week. An established Australian polling firm, Freshwater Strategy, have been doing polls here, too. Stuff reports that the poll (also, at the Post)
…reveals 37% of New Zealand voters have seriously considered emigrating to Australia in the past 12 months.
By comparison, of Australian voters, only 8% have considered moving to New Zealand, including just 1% who have spent time looking into it.
If you don’t think too carefully, that gives the impression of a giant sucking sound and the lights going out in New Zealand. Australia is a lot larger than New Zealand, though. If 8% of people in Australia moved to New Zealand and 37% of people in New Zealand moved to Australia, the population of New Zealand would go up, not down. The total populations are about 5 million and about 27 million. Of those, about 3.6 million are enrolled to vote in NZ and nearly 18 million enrolled to vote in Australia, so 37% of NZ voters is 1.3 million and 8% of Oz voters is 1.44 million.
Another useful comparison number is that the largest ever number of people migrating out of NZ to all destinations, not just Australia, over any 12 months is about 130,000, a tenth of the ‘seriously considered’ number. A lot of people (apparently) seriously consider a lot of things they don’t end up doing.
The other important aspect of the story is the estimates quoted for small subpopulations. Overall, the poll claims a maximum margin of error of about 3 percentage points. That’s for the population as a whole. Proportions are given for different age groups, including 18-34 year olds, people earning more than $150,000, and voters for Te Pāti Māori. We aren’t told the uncertainty in these numbers, but it’s obviously higher. About 1/3 of adults are 18-34, about 5% earn over $150k (IRD spreadsheet), and about 3% voted for Te Pāti Māori. The maximum margin of error for subpopulations this big would be 5, 13, and 17 percentage points respectively, assuming equal sampling. You can’t easily learn much about wealthy people or Pāti Māori voters just by contacting random people throughout the country — and the assumption that you can make your sample representative by reweighting gets increasingly dodgy.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
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Scott you are the one abusing statistics in this case. When you are comparing countries of different sizes, percentage of population is about the only way to compare them, and unless you are a politician, it should be the only way to compare them.
If 14 million Chinese decided to move to Australia tomorrow it would increase our population by 50% and decrease theirs by 1%. Likewise if 14 million Australians decided to move to China it would half our population and increase theirs by 1%. What are the significant numbers here, the absolute number or the percentage of the population?
2 days ago
Sorry, I should say Thomas. Or Mr Lumley.
2 days ago
I disagree completely. Suppose we considered just internal movement within Australia. In a stable situation, as many people would move from Victoria to Tasmania as from Tasmania to Victoria. That same number would be a larger fraction of Taswegians than Victorians, but that’s what you need for a stable situation. If you had the same fraction for both states you’d get a massive migration to Tasmania. My argument is that the natural null model here is an equilibrium flow, and that equal proportions in the two countries is actually quite unnatural as a null.
10 hours ago
Yes, but if you use the number who move as a measure of dissatisfaction with living arrangements, then the measure needs to be standardized to compare different populations. The percentage is simply the way to standardize raw numbers. If 10% of Victoria wants to move and 10% of Tasmania wants to move, then the level of dissatisfaction would be equal even though the absolute numbers are unequal.
8 hours ago
No, that’s exactly what I’m contesting. I don’t think equal proportions considering moving is a good null model **precisely because** it is incompatible with any population equilibrium.
Suppose you take a homogenous country where population attitudes and the distribution of satisfaction are the same everywhere and and population flows are stable, and you get a toddler to draw arbitrary lines on it to make smaller units such as states. The only way the migration probabilities **aggregated to the state level** can be equal is if the states all have the same population. However, migration counts will be approximately equal between states. That’s why I think equal migration probabilities is a bad null model and equal counts is better
The problem is the boundaries: if you’re in Australia there a lot of places you can move to that are also in Australia. If you’re in NZ then fewer of the places you can move to are in the same country.
5 hours ago