New Zealand Period Life Tables

Most life tables are period life tables which commence with a hypothetical group of newborn babies, and assume that they experience the observed mortality rates of a given period throughout their life. The derived life expectancies give an indication of the average longevity of the population but do not necessarily reflect the longevity of an individual.

**Older ages ** Prior to 2012–14

For most ages above 90 years, death rates of the total New Zealand population have been modelled on the mortality trends of other countries such as Australia, Canada, Japan, United Kingdom and United States. At the older ages it is assumed that the rate of change in probability of dying within a year (qx) decreases linearly with increasing age. For the Māori and non-Māori populations, death rates have also been modelled at ages in the early 80s and late 80s, respectively.

For 2012–14

A demographic analysis using cumulated counts of deaths from the highest ages was used to compare counts of the population previously alive (‘extinct generation method’) with the estimated resident population for each population group at 30 June for both 2006 and 2013. As a result of this analysis, ages 100 years or over are represented by one open age group in the life tables, and life table calculations use population data generated by the ‘extinct generation method’ for the oldest ages.

For 2017–2019 Introduced monotonic regression spline to smooth the observed death rates at ages 85 years and over. The smoothed death rates at ages 85+ improve the plausibility of estimated death rates at these ages and are used to construct the life tables for the national level populations. The use of smoothed death rates for the oldest ages has a very small impact on the life expectancy at birth measure.

Ethnic groups

Ethnic populations are not mutually exclusive because people can and do identify with more than one ethnicity. People are not asked to prioritise their ethnic responses. Hence, StatsNZ includes people who identify with more than one ethnicity, in each of their reported ethnic groups.

Ethnic identification can change over time. This may reflect a person's cultural affiliations changing over time. Or, it may occur when different people respond to the ethnicity question. For example, the ethnicity of babies and young children is usually identified by their parents however, in a later census when these individuals are old enough to complete their own forms, they may choose a different ethnicity. Inter-ethnic mobility can also occur when different ethnicities are reported in different collections (eg birth registration form, death registration form, census form) for a person.

There are greater difficulties in establishing past trends in fertility, mortality and migration. Different ethnicities can be reported in different collections (eg birth registration form, death registration form, census form), which makes the derivation of ethnic-specific fertility and mortality rates problematic. Furthermore, the measurement of ethnicity has changed over time in many collections, while it is not captured at all in some collections (eg external migration data).

There is greater future uncertainty about the components of population change. For example, it is uncertain whether the fertility and mortality of different ethnicities will converge, and if so, at what pace. Assumptions about future migration, notably for people of Asian and Pacific ethnicities, are particularly susceptible to changes in migration patterns.

There is the added complication of births to parents of different ethnicities. The child may be considered by the parents to belong to one or more of their ethnicities, or indeed to another ethnicity.

Deaths numerator

The life tables were compiled from deaths registered, rather than deaths occurring. Most death statistics refer to registrations rather than occurrences for a given time period, because of the time lag between when the death occurred and when it is registered. Hence, for a given time period, the number of death registrations can be confirmed before the number of death occurrences.

For periods of a year or more, the difference between registrations and occurrences is generally small, so death statistics referring to registrations are suitable for most purposes.

An allowance for ethnic non-response among deaths was also made. There was no response to the ethnicity question for about 2.4 percent of deaths in 1996–97, 3.5 percent of deaths in 2000–02, 4.9 percent of deaths in 2005–07, 0.7 percent of deaths in 2010–12, 0.2 percent of deaths in 2012–14, and 0.1 percent of deaths in 2017–2019. Because deaths in the first year of life are skewed towards the early part of this age, infant death rates were calculated from more detailed data. This involved the division of the first year of life into more detailed ages.

Population denominator (exposed-to-risk population)

Usually the mean population for a period is used as the denominator to calculate death rates. However, mean population estimates are not available for all ethnic populations. To ensure consistency of method among all population subgroups, the estimated resident population at 30 June (the midpoint) was used. The impact of using ‘midpoint’ rather than ‘mean’ population estimates is generally insignificant.

The estimated resident populations at 30 June 1996, 2001, 2006, 2013, and 2018 were based on the census usually resident population counts at 5 March 1996, 6 March 2001, 7 March 2006, 5 March 2013, and 6 March 2018 respectively, and adjusted for:

• non-response to the census ethnicity question (not 2018 census)
• net census undercount
• residents temporarily overseas on census night
• births, deaths and net migration between census night and 30 June of the census year
• reconciliation with demographic estimates at ages 0–4 years (0–9 for 2013, 0–14 for 2018).

Note: All population estimates used in the 1995–97 to 2017–2019 life tables have been derived using the same methodology (2018 ERP used outcomes-based migration as an improvement). In addition, the ethnicity question used in the 1996 Census is the same as that used in birth and death registration forms from September 1995. The use of population estimates based on the 1996 Census also allows the adjustment ratios presented in Ajwani (2003) to be incorporated.

• Statistics New Zealand
• Insurance and Actuarial companies
• Ministry of Health
• Health planners
• Social researchers

1996

Population concept used in the calculation of mortality rates changed from de facto to resident.

The population concept used for population estimates and projections changed from de facto to resident.

The de facto population includes all persons in New Zealand at a given time. It includes overseas visitors, but excludes residents temporarily overseas and net census undercount.

The estimated resident population includes the estimated net census undercount and the estimated number of residents temporarily absent overseas, but does not include overseas visitors.

Resident population estimates do not show the quarterly fluctuations that de facto estimates are subject to because of seasonal changes in the numbers of overseas visitors temporarily in New Zealand, and changes in the numbers of New Zealand residents temporarily out of New Zealand.

The definition of Māori used for population estimates has changed over the years.

Before 1986

Māori population estimates were based on people with half or more Māori blood.

1986–1991

The term 'sole Māori' was used between the 1986 Census and the 1991 Census to describe those census respondents who stated New Zealand Māori as their sole ethnic group. These estimates were of the de facto population. Māori births and deaths (defined as being with half or more of Māori blood) were used to update the base population at census. Māori net migration was assumed to follow the same pattern as applied over the period 1982–1986 (ethnicity information was not collected on external migration cards after 1986).

1991 Onwards

Māori population estimates refer to people belonging to the Māori ethnic group. These estimates are based on the census usually resident population counts of the Māori ethnic group at the 1996, 2001, 2006, and 2013 Censuses, updated for net census undercount;

• the number of residents temporarily overseas on census night,
• births, deaths and net migration (excess of arrivals over departures) between census night and 30 June,
• reconciliation with demographic estimates at the youngest ages
• non-response to the census ethnicity question.

Sept 1995

Changes to the ethnic question on the birth and death registration forms means that the ethnic classification is not by degree of blood, but rather, self-identification. This also means that a greater range of ethnic groups can be identified and multi-ethnic responses can be generated. See Births and Deaths Profiles.

2001

The ethnic question in the 2001 Census of Population and Dwellings changed from that asked in 1996. (The 2001 question was very similar to that asked in 1991.) As a result, the ethnic data from the 2001 Census is not comparable with that from the 1996 Census. This change means that 1996-base population estimates for the Māori ethnic group are not comparable with the 2001-base population estimates. Consequently, estimates for the Māori ethnic group were revised back to 1991, using results from the 2001 Census.

2002

The base populations for the Māori, Pacific, Asian, and European ethnic groups, at 30 June 2001 incorporate an adjustment for those people not specifying their ethnicity. This is the first time the base estimated resident populations have included such an adjustment.

A revision of the estimated resident populations for the period 1991–2001 was carried out in September 2002. The revision was necessary for two reasons. Firstly, the 2001 Census and the 2001 Post-enumeration Survey (PES) allowed a new base population for population estimates to be defined at 30 June 2001.

Secondly, a revision of population estimates based on the 1996 Census was necessary, as analysis of the 2001 PES results led to revised estimates of undercoverage in the 1996 Census, from 1.2% to 1.6% in total. About 16,000 residents were added to the 1996-base population because of the revised undercoverage estimates. Population estimates for the period 1991–1996 use the revised 1996-base population.

2015

The 2012–14 New Zealand life tables used a statistical model for deriving measures of mortality and life expectancy that is consistent across all population groups. This new statistical model was developed to estimate the death rate at each age (0, 1, 2, ..., 100+) by sex for each of the population groups. The 2012–14 period life tables release includes life tables for the 2005–07 period based on this new method, for comparison with results using the previous method.

Note: previously released 2005–07 life tables remain suitable for use as the official series, for all life tables except Asian, and European or Other life tables, which are only available using the new methods from 2005–07.

For the 2012–14 release, we compared estimated death rates by age using the statistical model with observed death rates. The statistical model also provided a measure of uncertainty for each of the life table functions.

The latest release includes the median as well as 95 percent limits. For example, the true value of the death rate will be within the 2.5th and 97.5th percentiles, 95 percent of the time, given the input data and the assumed statistical model

Note: The 2010–12 interim period life tables have been superseded by the 2012–14 period life tables.

2021 Further improvements of the statistical model being developed to derive the 2017–2019 life tables. Extend the age for total population group to 105.

6. Five-yearly