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Frequently asked questions - Population statistics
Frequently asked questions - Population statistics (Part 1)

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:

What is the difference between census counts, population estimates and projections?

The Census of Population and Dwellings is a five-yearly survey providing a wealth of data for: small geographic areas; variables such as occupation and country of birth; individuals, families, households and dwellings.

In between censuses, population estimates by age-sex are prepared to give an indication of change since the last census. The estimates also include people not counted by the census, either because they were temporarily overseas or missed by census.

For those interested in planning, projections (of population, households, families and labour force) are derived to give an indication of future change. 

There are differences between the most common population measures which can be illustrated as follows:

Census usually resident
population count

 

Estimated resident
population

 

Population
projections

 

 

 

 

 

 

Residents in New Zealand
on census night

 

 

Residents in New Zealand
on census night

 

 

Residents in New Zealand
on census night

 

 

Residents missed by census
(net census undercount)

 

Residents missed by census
(net census undercount)

 

 

Residents temporarily overseas
on census night

 

Residents temporarily overseas
on census night

 

 

Births, deaths, and net migration
since census night

 

Assumptions about future fertility,
life expectancy, and net migration

Census

The most commonly used census measure is the 'census usually resident population count'. This is a count of all people who usually live in New Zealand, or in an area of New Zealand, and are present in New Zealand on a given census night. This count excludes visitors from overseas and excludes residents who are temporarily overseas on census night. For a subnational area, this count excludes visitors from elsewhere in New Zealand (people who do not usually live in that area), but includes residents of that area who are temporarily elsewhere in New Zealand on census night (people who usually live in that area but are absent).

The 'census night population count' is a count of all people in New Zealand, or in an area of New Zealand, on a given census night. This count includes visitors from overseas and excludes residents who are temporarily overseas on census night.

Estimates

Population estimates ('estimated resident population') are higher than the 'census usually resident population count' because the estimates make an allowance for net census undercount and residents who are temporarily overseas at the time of the census. Population estimates are prepared annually for local areas to give an indication of population change since the last census. The estimates are updated for births, deaths and net migration (external and internal) since the last estimate. The 'estimated resident population' measure was introduced after the 1996 Census when a post-enumeration survey was conducted for the first time.

Projections

Population projections use population estimates as a starting point and are an indication of future demographic change based on assumptions about future demographic behaviour.

Further information is available in the Statistical Standard for Population Terms.

What geographic levels are available?

Census counts are available for geographic areas as small as 'meshblocks'. Meshblocks are usually aggregated to larger geographic areas because of confidentiality provisions and to include additional census variables (eg age, ethnicity, labour force status).

Population estimates and projections by age-sex are available at the area unit ('suburb') level. They are often aggregated to larger geographic areas such as territorial authority areas and regional council areas. Further information is available on area unit population projections.

When are the different population statistics available?

Census

A Census of Population and Dwellings is held in New Zealand every five years, typically in early March in years ending in 1 or 6. The 2011 Census was cancelled due to the Canterbury earthquakes. A Census was held in 2013 and the next one will be in 2018. Final results are available within a year of the census: Output from the 2013 Census and Output from the 2006 Census.

Estimates

National population estimates are produced quarterly (reference dates at 31 March, 30 June, 30 September and 31 December) and provisional results are available within 6 weeks of the reference date. Subnational population estimates are produced annually (reference date at 30 June) and are available in October. After each census the population estimates for the preceding intercensal period are revised. For example, following the release of results from the 2013 Census and the 2013 Post-enumeration Survey, a new estimated resident population at 30 June 2013 was calculated. This new base is used to revise the previously published population estimates for the period 2006–13.

Projections

Demographic projections are updated and released every 2–3 years.

How many people does the census miss?

The post-enumeration survey run shortly after the census, estimated that the census counted 98.4 percent of the New Zealand population in 1996, 97.8 percent in 2001, 98.0 percent in 2006, and 97.6 percent in 2013. This compares favourably with other countries (eg Australia 97.3 percent in 2006 and 98.3 percent in 2011; Canada 97.7 percent in 2011). The high response reflects the cooperation and support of the New Zealand public. However, estimated census coverage does vary across the population. For example, males are more likely to be missed than females; young adults are more likely to be missed than older adults; Maori, Asian and Pacific people are more likely to be missed than other ethnic groups.

In addition to net census undercount, there is non-response where substitute records are created. More details can be found in Coverage in the 2013 Census based on the New Zealand 2013 Post-enumeration Survey and Understanding substitution and imputation in the 2013 Census. Those people missed by the census are often in population sub-groups important to government policy formulation, so Statistics New Zealand makes concerted efforts to maximise census coverage.

What basic components underlie the population estimates?

The estimated resident population of an area is derived by:

  1. updating the 'census usually resident population count' (from the most recent census) to take account of net census undercount and residents temporarily overseas on census night; and
  2. updating for births, deaths, net permanent and long-term external migration and net internal migration between the census date and the date of the estimate.

Birth and death data are obtained from birth and death registration forms, which have a high level of coverage and general accuracy. Permanent and long-term migration data are obtained from arrival and departure cards completed by every passenger arriving in or departing from New Zealand. Internal migration is estimated using a range of symptomatic data including electoral enrolments, school rolls, residential building consents, historical internal migration data, and any relevant information supplied from each local authority.

Further information is available on population estimates.

What basic assumptions underlie the population projections?

Population projections are derived from an assessment of historical, current, and likely future trends in births, deaths, and migration – the three components of population change. Assumptions about future fertility (births), mortality (deaths), and migration are formulated after analysis of short-term and long-term historical trends, government policy, information provided by local planners and other relevant information. Assumptions are set first at the national level and used as a constraint for the subnational assumptions (this 'top-down' approach prevents implausible projections for any area).

Fertility

Fertility assumptions for each area are formulated in terms of age-specific fertility rates for each time period. The rates are based on the recent number of registered births in each area. The rates are then applied to the (female) population in each area to give the number of births for each time period.

Mortality

Mortality assumptions for each area are formulated in terms of male and female age-specific survival rates for each time period. The rates are based on the recent number of registered deaths in each area. The rates are then applied to the population in each area to give the number of people who survive each time period (the number of deaths is calculated indirectly).

Migration

The assumed net migration level and age-sex pattern for each area is based on a consideration of observed past patterns, the capacity of the area for further growth (for areas with net inflow), whether historical outflows can be sustained (for areas with net outflow), and information available from and about local authorities relating to current and future developments which may affect population change.

Further information is available on projection assumptions.

What use are population statistics?

The population is always changing in number and its characteristics. Information about the population helps governments, communities and businesses evaluate how past decisions and policies have performed, and how future decisions and policies should be shaped. For more information see Census community stories.

Population projections assist planning for the future. While information about the past and current size and structure of the population is useful, information about the likely future size and structure of the population helps government and communities to plan infrastructure and facilities to meet the needs of a changing population. The projections are not predictions, but an indication of likely future change given specific assumptions about future fertility (births), mortality (deaths) and migration.

Which projection series should I use?

Alternative projection series are always produced by combining different assumptions about the components of population change. The different series help illustrate a range of possible scenarios, although are not designed to cover every possibility. Users can, and should, make their own judgement as to which series is/are most suitable for their purposes. However, at the time of release, Statistics New Zealand considers the mid-range projection series (eg 'medium' series) the most suitable for assessing future population changes. All the mid-range projection series (ie national, subnational; population, ethnic population, family and household, labour force) are produced to be consistent with each other.

What is meant by 'the demographic transition' and 'population ageing'?

The demographic transition refers to the shift from relatively high fertility rates and high mortality rates to, first, relatively low mortality rates, and subsequently to relatively low fertility rates. Population ageing refers to the gradual transformation of the age structure and is intrinsically linked with the demographic transition. Both the transition and ageing has occurred, or is occurring, in other countries, often at a much faster pace than being experienced in New Zealand. For more information see Demographic Aspects of New Zealand's Ageing Population.

What is meant by 'sub-replacement fertility'?

This refers to a total fertility rate below 2.1 children per woman (replacement level), which is the average number of children each woman is required to have for a population to replace itself in the long term, without migration.

Although fertility in New Zealand has generally been below replacement level since the 1970s, the population still has considerable built-in momentum for growth. The number of babies born today is partly predetermined by the number of females born 20–40 years earlier while death numbers are largely predetermined by the number of births occurring 70–90 years earlier. Thus, despite sub-replacement fertility, natural increase (excess of births over deaths) added more than 30,000 people a year to New Zealand's population in 2005–11. Natural increase is projected to decline steadily over the next few decades. And as those generations who opted for low fertility enter the older ages, deaths will increasingly exceed births (natural decrease) in many areas of New Zealand (as is happening in many other countries).

An immediate return to high levels of fertility would not increase the number of women of childbearing age for several decades. Thus, just as it has taken decades for the full effects of sub-replacement fertility to be felt, it would take time for the population to overcome inertia and re-adjust to higher fertility.

Are there standard definitions of 'baby boomers', 'generation X', and 'generation Y'?

Baby boomers are usually regarded as those born in the years 1946–65, although the definition of the baby boom period varies between sources and between countries. The baby boom was associated with high fertility rates and high numbers of births. New Zealand's annual total fertility rate was at least 3.5 births per woman during 1946–65, and at least 3.0 births per woman during 1945–72.

Generation X and generation Y are essentially marketing terms, common in the United States, and are less obviously tied to an observable demographic phenomenon unlike the baby boomers. Statistics NZ has no official or standard definition of generation X and generation Y.

If one subscribes to the 1946–65 baby boom working definition, then generation X could be the 15-year period after the baby boom (1966–80) and generation Y could be the 20-year period after generation X (1981–2000).

Why is there a discontinuity in population estimates in 1991?

There is a discontinuity in national population estimates in 1991, caused by a shift from 'de facto' to 'resident' population estimates. For information on how to cope with the discontinuity, see Coping with the discontinuity in population estimates.

Further information

Further information on population statistics is available in part 2 of our frequently asked questions.

Page updated 28 August 2014

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