Census ‘anomalies’ leave council staff scratching their heads

Nicole Mathewson Reporter from The Press

By David Hill, Local Democracy Reporter

‘‘Anomalies’’ in Census data on North Canterbury's population growth is creating a headache for a local council.

The Hurunui District Council’s south ward, including Amberley, has experienced a building boom in recent years, but this is not reflected in the latest provisional Census data on population growth.

According to Census data released earlier this year, Hurunui’s south ward had a population of 5620 in March 2023, an increase of 410 people from the 2018 Census.

This suggests an increase of 1.53% a year over the last five years, much lower than the yearly average increase for the ward of 2.45% since 2001.

But council chief executive Hamish Dobbie said the council’s own data suggests a much larger population increase.

‘‘We would rate the period 2018 to 2023 as a high growth period. You’ve just got to look at the number of houses being built.

‘‘Maybe when they did the Census, people weren’t in their houses and did it somewhere else.

‘‘There is something that doesn’t add up, or maybe it is right and the population was over estimated in 2018.’’

A Stats NZ spokesperson said the current calculations are subject to change and net migration can be difficult to estimate.

Over the last five years, the council has issued 373 consents for new houses in the south ward, mostly for three or four bedroom houses.

Dobbie did not believe there were lots of empty houses in Amberley.
If Census data is unreliable, it can complicate council planning, he said.

But he acknowledged predicting population is ‘‘an inexact science’’.

‘‘It is when you don’t know there are anomalies that you can get things wrong.’’

When the council conducted a representation review ahead of next year’s local government election, it had to rely on 2018 Census data as the 2023 data was not available.

A rapidly rising population formed part of the reasoning behind a proposal to establish a community board for the south ward.

But when presenting to the Local Government Commission last week, the council presented the 2023 Census data while noting the number consents issued.

‘‘We do our own numbers for planning for things like water supply,’’ Dobbie said.

‘‘If we utilised growth numbers that come from the Census, we wouldn’t have water available when it is needed.’’

A Stats NZ spokesperson said the figures for Hurunui’s south ward compared the 2018 Census with population estimates and projections.

‘‘Estimated population change for an area comes from estimated natural increase (births minus deaths), plus estimated net migration.’’

Migration is hard to estimate because there is no single authoritative data source to measure migration into and out of an area, the spokesperson said.

‘‘Estimates for June 2023 are provisional and subject to revision,’’ the spokesperson said.

Building consents are useful, but not all consents result in completed houses, there is a lag between consent and occupancy, some are for second homes and some are to replace demolished buildings.

A second release of 2023 Census data is due on October 3, while population estimates will be revised next year.

Local Government Minister Simeon Brown said the Government is not considering allowing alternative data sources to be considered in representation reviews.

"Representation review data looks at the entire population, not just ratepayers or those eligible to vote, so care would be needed in considering whether alternative data sources could be used in the future.''

■ LDR is local body journalism co-funded by RNZ and NZ On Air.