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How to Read Census Housing Data Without Getting It Wrong

Census housing data is the best information New Zealand has about what living somewhere costs, and the most misread. This site publishes it for 2,210 areas, and every one of those pages follows five rules that this guide explains once, properly. They are not pedantry: each rule exists because breaking it produces a confident number that is wrong, and confident wrong numbers about housing get quoted.

Rule one, the denominators. An area page shows a median weekly rent and a median household income, and the obvious move is to divide them into a rent-to-income ratio. The two figures stand on different populations: rent is measured over renting households only, income over all households, owners included. Owners generally have higher incomes than renters in the same area, so the ratio understates the burden on the people actually paying the rent, by an amount that varies area to area. The division produces a number that describes nobody, which is why no page on this site computes it, and why a checker fails the build if one starts to.

Rounding, and areas that are not suburbs

Rule two, random rounding. Every count is randomly rounded to base three before Stats NZ publishes it, to protect individuals in small cells. Random means random: 348 owned plus 147 rented plus 57 in trusts need not equal the stated 552 total, because each figure was rounded independently. Read differences of a few as the rounding they are. The corollary matters more: the smaller the count, the larger the rounding is proportionally, so a figure describing a dozen households is soft in a way a figure describing a thousand is not.

Rule three, the geography. A statistical area 2 is a Census unit of roughly two to four thousand people. It is drawn for statistical usefulness, not to match anyone's mental map: sometimes it is the suburb people would name, often it splits one in two or bundles three villages. Two practical consequences. Comparing your suburb against an SA2 figure needs a look at what the SA2 actually covers, which its name sometimes only hints at. And a boundary street can genuinely sit in the statistical area next door, so the neighbouring areas, listed with distances on every page, are part of any honest reading.

Rule four, measured zeros against missing data. A dash on an area page means Stats NZ published no figure. A zero means a measured zero: Burnham Military Camp records zero owning households because nobody there owns, not because data is missing. The two look similar and mean opposite things, and pages that conflate them corrupt every average built on top.

The silence in the middle: no mortgage figure

Rule five, the missing number. The Census asks renting households what they pay and does not ask owning households the same question. There is no Census median mortgage payment for any area in New Zealand. The gap is invisible until you notice every area page discussing rent in dollars and ownership only in shares, and it catches out professionals: any area mortgage figure attributed to the Census is a confusion with some other source.

What fills the gap honestly is arithmetic, not data: current prices for the area, current rates, and the mortgage repayment calculator. That is why the area pages link the calculator rather than print a number the source cannot support.

Kept together, the five rules turn the area pages from a table of numbers into evidence: real rents by area for the rent decision, tenure shifts for the ownership story, and ten-year movements for the rent-rise league, each standing on figures used within their limits.

Test Your Knowledge

Quiz on reading the data

1. Why must an area's median rent never be divided by its median household income?
Rent is measured over renting households and income over all households, so the ratio describes a population that does not exist
Because rent is weekly and income is annual
Because the Census forbids derived statistics
It can be divided; the ratio is standard practice
2. An area's tenure counts sum to 546 but the stated total is 552. What happened?
A data entry error
Random rounding to base three: each figure is rounded independently, so components need not sum to totals
Six households were double-counted
The total includes empty dwellings
3. What is a statistical area 2?
An official suburb boundary
A Census geography of roughly two to four thousand people, which may match, split or bundle the suburbs people actually name
A school zone
A postcode area
4. What does the Census tell you about mortgage payments in an area?
The median payment, alongside the median rent
Nothing: it does not ask owning households what they pay, so no Census mortgage figure exists for any area
Only the interest component
Payments for new mortgages only
5. What is the difference between a dash and a zero on an area page?
A dash means no figure was published; a zero means a measured zero, like a military camp where nobody owns
They mean the same thing
A dash means the figure was suppressed for being embarrassing
A zero means the area no longer exists

Frequently Asked Questions

Can I compute a rent-to-income ratio from an area page?

No: the two medians stand on different populations, renters against all households, and the ratio describes nobody. It is the most common misuse of this data.

Why are small areas missing?

185 areas fall under the floor of 100 households and have no page, because random rounding makes their figures more noise than measurement. Every exclusion is recorded with its reason.

Where does the data come from?

Stats NZ's Census tables for households by statistical area 2, for 2013, 2018 and 2023, retrieved through the official geographic data service.

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