Period analysis | Permanent and long-term migration | Population density | Population estimate | Population growth | Population projection | Population pyramid | Prevalence |
Rate of population change | Replacement fertility | Resident | Second demographic transition |
Standardisation | Statistical standard for population terms | Subject population | Synthetic cohort | Total fertility rate | Trend | Vital statistics
Period analysis
Comparing the characteristics of a population or particular groups within a population at one or more points in time. Also known as cross-section analysis, and contrasted with cohort analysis.
Permanent and long-term migration
This comprises permanent and long-term arrivals and permanent and long-term departures. The former are people who have either spent the last 12 months or more overseas, or arrive in New Zealand for an intended stay of 12 months or more (or permanently). Permanent and long-term departures are people who depart from New Zealand for an intended absence of 12 months or more (or permanently).
Population density
The average number of people per square kilometre (or hectare) in a given area.
For example, the estimated density of New Zealand at 30 June 2001 was 14.5 people per square kilometre (0.14 people per hectare).
Population estimate
Estimate of the number of people resident in an area at a particular time. Population estimates (and population projections) are key inputs to policy analysis and service planning. For details of issues and methodology, see here.
Population growth
The prevailing fertility, mortality, and migration patterns combine to determine the level of population growth. Population growth is calculated by adding natural increase (number of births less the number of deaths) and net external migration (inflows minus outflows).
Population projection
Estimate of the future size and other demographic characteristics of a population, based on an assessment of past trends and assumptions about the future course of demographic behaviour (fertility, mortality, and net migration).
They are plausible scenarios, not forecasts or predictions. Projections typically involve several sets of assumptions (low, medium, high) for each of the main components, resulting in a set of alternative projections (variants) that reflects the uncertainty involved. Where data from only one set of projections are presented, by convention this should be for the medium variant.
For details of issues and methodology see here.
Population pyramid
See age-sex pyramid.
Prevalence
Prevalence measures the total number of cases of a condition (eg disease or disability) in a population. The prevalence rate refers to the total number of cases divided by the subject population.
Rate of population change
Change in population size during a period divided by the population at the beginning of the period. This is often expressed as the annual rate of growth or the average annual rate of population growth (over a five-year period, for example), usually expressed as a percentage.
The average annual rate is calculated using a standard growth function. For example, a constant rate of change of 10 percent per annum would result in a total growth of 61 percent over a five-year period because the increments compound.
Two aspects of this measure are noteworthy. In this example, the 61 percent growth does not represent an average of 12 percent per annum. The average growth rate does not imply that the growth rate throughout the period was constant. Data may indicate an inherent seasonality in the process which impacts directly on policy.
Replacement fertility
Generally refers to a total fertility rate of 2.1 children per woman, which equates to the average number of children each woman is required to have for the population to replace itself in the long-term. The rate reflects the sex ratio at birth (roughly 105 males born for every 100 females) and mortality of females between birth and childbearing.
Resident (also referred to as Usual Resident)
A person who usually lives in an area. This is a statistical, not a legal, definition generally based on a person's self-identified usual address. New Zealand residents are people who live permanently in New Zealand (including people temporarily overseas)
In census statistics, a resident is a person who self-identifies on the census individual form that they usually live in an area (for example, an overseas resident is somebody who has stated that they usually live overseas).
In external migration statistics, a resident is a person who self-identifies:
Second demographic transition
Refers to the effects of continuing below-replacement fertility in the majority of developed countries.
This transition is not seen as part of the demographic transition (which envisaged a simplistic trend towards a balance between births and deaths in the long term), but as a response to a new set of circumstances which were partly a consequence of the first transition and partly related to changes in population mobility and diversification.
Standardisation
Standardisation is one type of weighted average. When comparing two or more populations it is essential to ensure that the populations are as comparable as possible.
Frequently, the populations being compared will have very different age structures, for example, and need to be standardised against a reference population.
Standardisation takes into account differences in the distribution of some centrally important characteristic (such as age) within the populations under consideration, addressing the question: if these different populations were to have the same age structure (or that of the whole population or some other reference group), how would the rates then compare?
This is critically important in comparing different populations (say, of an area or between groups of different ethnicities) with significantly different structures.
An explanation of the method for both direct and indirect standardisation can be found in the Ministry of Health's Standardising Rates of Disease.
Statistical standard for population terms
A standard set by Statistics New Zealand to aid understanding of different population measures. It is important that users are aware which population measure has been used when comparing data from different sources.
Historically, population data comprised counts of all people present in a given area at a given time (de facto). However, increased geographic mobility means people are more likely to move between New Zealand and overseas, and between areas of New Zealand, for work, study and holidays.
There is, therefore, a need for population data about the people who usually live in an area at a given time (de jure), as this is more relevant for many planning purposes (for example, housing and schools).
This standard explains the differences between the three main population measures produced by Statistics New Zealand (census night population count, census night usually resident population count, and estimated resident population) so that population data will be easier to understand.
Previously, no standard terminology or definitions existed for these population measures. Also, because the concepts overlap and are complex, the comparability of the different population measures has not been well understood.
See the standard on the Statistics New Zealand website.
Subject Population
The subject population comprise the people who are relevant to a particular enquiry.
For example, the Asian ethnic group in New Zealand consists of people who usually live in New Zealand and have identified themselves to be of at least one Asian ethnicity. In this case it is important to note that some of the people in this group may also belong to other relevant groups (eg they may also be of Pacific ethnicity).
The identification of the correct subject population is vital.
For example, the proportion of the population which belongs to the Asian ethnic group is calculated by dividing the number of people with at least one Asian ethnicity by the total number of people in the subject population who specified their ethnicities. Excluding non-respondents from this type of calculation is extremely important because the distribution of a characteristic within the non-responding group is likely to be very different from the distribution of known responses if the level of non-response is significant. See also Which population?
Synthetic cohort
A hypothetical cohort of people used to derive a measure from data for a specified period as though they represent life time experiences of actual cohorts.
For example, the total fertility rate represents the average total children born per woman for a synthetic cohort of women with age-specific births rates of the reference period.
Total fertility rate
The average number of live births that a woman would have during her life if she were to experience the age-specific fertility rates of a given period (usually a year).
Trend (of a series)
The implied long-term change in a series. In general, the trend gives a better prognosis of change because it removes the distraction of short-term turbulence in a series.
Vital statistics
Statistics of events related to births, deaths, and marriages.