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Frequently asked questions - Population statistics
Frequently asked questions – Population statistics (Part 2)

Population statistics produced by Statistics New Zealand include census counts, population estimates, and population projections. 'Frequently asked questions' provides information on commonly asked questions about population and population statistics.

This page contains information on the following questions:

How can Statistics New Zealand know more about a local area than people who live there?

Statistics New Zealand is in regular contact with analysts and planners in every local authority who provide information about local developments which may affect the population. This includes an annual consultation each July enquiring about local developments, and liaison with local planners every two to three years seeking information about likely future developments (eg subdivisions, zoning changes) at an area unit ('suburb') level. Local authority websites are an increasingly useful source of local information. Statistics New Zealand also visits local areas as part of its extensive census consultation and planning. Statistics New Zealand staff are often involved in presentations to, and discussions with, local areas.

So although Statistics New Zealand may not know more about an area than local residents, it is likely to know more about the rest of New Zealand. The end result is a comprehensive picture of New Zealand's changing demographic make-up.

Why can population estimates/projections contradict trends in housing numbers?

Although houses are being built, this may not translate into more people residing in an area due to a number of factors including reduced occupancy rates (ie fewer people per household on average), the building of holiday homes, and new buildings replacing demolished houses.

The changing age structure of the population is also important. In some areas the total number of people may be projected to decline. However, there may be opposite trends in the number of children (eg decreasing) and adult population (increasing). Clearly, the impact of children and adults in the housing market is very different.

Indeed, Statistics New Zealand's family and household projections indicate that households are growing faster than population. In some areas more households are likely despite fewer people. This reinforces the importance of the projections in providing information about the changing age structure, which is at least as important as changes in total numbers. 

How do population trends relate to trends in other indicators?

Indicators such as house sales, retail trade, electoral enrolments, school rolls, electricity use, water use, and car registrations can all change independent of population change. In some cases the indicators are influenced by visitors – people who usually live elsewhere and are therefore excluded from the population statistics for the area they are visiting. In some cases the indicators are affected by changing economic propensities (eg increased consumption per capita). In some cases the indicators are driven by a segment of the population (eg children, adults), which emphasises the importance of considering changes in age structure rather than focusing on total numbers of people.

What is the relationship between population change and economic growth?

The components of population change – births, deaths, and migration – do not necessarily relate closely to economic factors. This is because there are many more individual, local, national, and international factors which can interact and affect the population. Moreover, the number of people, families, and households may change independently of local economic factors.

It is important to note, therefore, that demographic projections should not be confused with economic forecasts. Changes in the number of people, families, or households do not necessarily relate to the social and economic well-being of an area.

Are visitors to an area included in the population estimates/projections?

Population estimates and projections measure the number of people usually living in an area. They therefore exclude people who are visiting for holiday, study, or work purposes but usually live elsewhere.

Measures of the resident population are particularly pertinent for electoral purposes and some service provision (eg schooling, libraries). For other services such as roads, sewerage, and health, measures of the service population – the population for which services are provided – may be more useful. However, defining and measuring the service population is problematic. The service population can vary depending on the service being provided. People may be counted multiple times in different areas depending on their mobility and use of services. And comprehensive information about different visitor groups (eg commuters, seasonal workers, daytrippers) in local areas is limited. For further discussion of these issues, refer to the Australian Bureau of Statistics working papers 'When ERPs aren't Enough' and 'Service Population Pilot Study'.

How do you decide if someone usually lives in an area?

In census statistics, a resident is a person who self-identifies on the census individual form that they usually live in an area. Guide notes for the 2013 Census included the following guidelines for usual address:

  • If you are an overseas resident and will be staying in New Zealand for less than 12 months, give your address in your home country. Otherwise, give your New Zealand address.
  • If you are a New Zealand resident, follow these guidelines to give the right address.
    • If you are a primary or secondary school student at boarding school, give your home address.
    • If you are a tertiary student, give the address where you live during term.

In external migration statistics, a resident is a person who self-identifies:

  • on the departure card that they have lived in New Zealand for 12 months or more, and/or
  • on the arrival card that they live in New Zealand and have been away from New Zealand for less than 12 months, and/or
  • on the arrival card that they intend to stay in New Zealand for 12 months or more (or permanently).

In birth registration statistics, the residence of the child is based on the self-identified "home address" of the mother. In death registration statistics, the residence of the deceased is based on their "usual home address" as identified by the family and/or funeral director.

How credible are Statistics New Zealand population estimates?

Statistics New Zealand provides independent (and free) population estimates (and projections) for every local authority area of New Zealand. Estimates (for past dates) and projections (for future dates) are based on an objective assessment of demographic trends in each area by a team of expert population analysts using the latest available population data. The public can be assured that the estimates and projections are not produced to satisfy the expectations of individuals or of individual local authorities.

How accurate are Statistics New Zealand demographic projections?

Demographic projections are not designed to be exact forecasts or predictions. Statistics New Zealand always produces a range of projection scenarios (eg low, medium, and high growth) to give an indication of likely future changes in the size and age-sex structure of the population. Users can, and should, make their own judgement as to which of the projections produced by Statistics New Zealand are most suitable for their purposes.

The projections are designed to assist both short-term and long-term planning needs and 'accuracy' is not necessarily the best measure of their usefulness. Indeed, the 'accuracy' of the projections can be irrelevant because users of projections, including central and local government, often use the projections to implement strategies to influence population dynamics. Statistics New Zealand updates the population projections every two to three years to ensure they reflect the latest demographic developments at the local and national level, and to maintain their relevance and usefulness.

This paper evaluates the accuracy of national and subnational population estimates and projections from 1991 to 2013: How accurate are population estimates and projections?

What is the difference between a projection and a prediction?

Statistics New Zealand does not make predictions but does produce a range of projection scenarios to give an indication of likely future changes in the size and age-sex structure of the population. At the subnational level, for example, a low, medium, and high projection is typically produced using specific stated assumptions about fertility, mortality, and migration. Although the assumptions are carefully formulated to represent future trends, they are not designed to provide an exact forecast. Users can, and should, make their own judgement as to which of the projection series produced by Statistics New Zealand is/are most suitable for their purposes. Moreover, the projections do not try to anticipate major policy changes which might have an influence on population.

The difference between projections and predictions is provided in an analogy made in Economic Implications of an Ageing Australia (2005) on the Australian Productivity Commission's website. They give the example of someone seeing a large boulder on a train track. The projection is that there will be a rail disaster and many deaths if the boulder is not moved or the train is not stopped. The prediction is that someone will move the boulder, averting the accident. It is likely that the projection the conditional forecast is much more useful for policy formulation and planning.

Why do you project population but not other factors (eg economic)?

Statistics NZ has produced population projections since the 1950s. There are several reasons why it does so. First, as a producer of census data and population estimates, population projections are complementary. Collectively, these data sources give information about past, current, and potential future population changes.

Second, roughly three-quarters of New Zealand's population in 20 years is already alive, as is half of New Zealand's population in 40 years, and everybody aged 65+ in 60 years. Only birth, deaths, and migration can affect population numbers. Only deaths and migration can alter the numbers of people already alive. Given some regularity in fertility, mortality, and migration patterns (although there are fluctuations in all of those), and barring major epidemics, war, or catastrophe, New Zealand's population can be projected with some confidence. Projections of sub-populations (eg for subnational geographies or ethnic groups) are more uncertain because of the added dynamics of internal migration and inter-ethnic mobility. In contrast, other factors (eg unemployment rates, inflation, gross domestic product) are directly affected by a myriad of factors which makes even short-term forecasts uncertain.

Finally, as with other statistics produced by Statistics NZ, there are advantages of having the independence and integrity of a national statistical organisation producing population projections. There is also the advantage of having a consistent set of projections produced for every area of New Zealand – consistency in terms of methods and consistency with national-level projections – rather than a fragmented set of projections produced by or for different local authorities.

Why are prioritised ethnic data not recommended?

Prioritisation re-classifies a person with multiple ethnic responses to just one ethnicity or ethnic group. There are several problems with choosing one ethnicity for a person who has said that they belong to more than one ethnicity:

  1. The ethnic question asks a person to choose which ethnic group or groups they belong to. The question accepts more than one answer and prioritisation goes against the principle of self-choice.
  2. People are not asked to specify one main ethnic group and do not know that prioritisation would make this choice for them.
  3. Prioritisation misrepresents the number of people who identify with an ethnic group. See The Impact of Prioritisation on the Interpretation of Ethnicity Data.
  4. Other countries which ask a similar ethnic question allow multiple responses and do not use prioritisation (eg United States, Canada, Australia).

Statistics New Zealand no longer prioritises ethnic responses but uses total response where people are included in each ethnic group that they identify with. This approach applies to all official statistics and is consistent with the findings from the 2004 Review of the Measurement of Ethnicity (available on Ethnicity Papers webpage). Statistics New Zealand can provide prioritised ethnic data as a customised request. For more information email or telephone 0508 525 525 toll free.

Are customised projections available?

Statistics New Zealand provides a comprehensive range of demographic projections for all areas in New Zealand. More detailed information than available from the website is often freely available, including more detail about the projection assumptions and projected age-sex composition.

Statistics New Zealand can also customise the projections including:

  • projections further into the future than published
  • subnational projections for non-standard age groups (eg 5–12 years, 17–19 years)
  • subnational projections for intercensal years (ie for years not ending in 1 or 6)
  • projections for different geographic units
  • projections incorporating different assumptions (eg specific net migration levels)
  • projections rounded to different levels
  • projections in different file types (eg xls, SAS, csv).

In some cases Statistics New Zealand will require the client to agree to the specified assumptions and identify this agreement in any dissemination of those projections. For more information and quotes, email or telephone 0508 525 525 toll free.

Further information

Further information on population statistics is available in part 1 of our frequently asked questions.

Page updated 25 September 2018

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