3222.7 - Population Projections, Northern Territory, 1999 to 2021  
Latest ISSUE Released at 11:30 AM (CANBERRA TIME) 25/07/2001   
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A. Method
The cohort-component method was used for these projections. In this method, the base population is projected forward annually by calculating the effect of births, deaths and migration within each age-sex group according to the specified fertility, mortality and migration assumptions.

These projections were produced in three stages. Firstly, the resident population of Northern Territory was projected by single year of age and sex. Secondly, the population of Darwin and Balance of Northern Territory was projected by single year of age and sex and constrained to sum to the projected population of Northern Territory for each year. Thirdly, each SLA within Darwin and Balance of Northern Territory was projected by single year of age and sex, and constrained to sum to the projected population of Darwin and Balance of Northern Territory, respectively, for each year.

B. Alternative series
The ABS has produced three alternative projection series using different combinations of assumptions on fertility, mortality, overseas migration and interstate migration.

Series Identifier
Fertility
Overseas Migration
Interstate Migration
A (high)
high
high
high
B (medium)
low
medium
medium
C (low)
low
low
low
Note: One mortality assumption was used in all series.

These three series for SLAs are consistent at the Northern Territory level with the three main series in Population Projections Australia, 1999 to 2101 (Cat. no. 3222.0) published on 17 August 2000.

C. Assumptions
C.1 Fertility
Two assumptions were made at the Northern Territory level:
1 The total fertility rate declines from 2.20 babies per woman in 1998 to 2.16 in 2007 and remains constant to the end of the projection period (high assumption).

2 The total fertility rate declines from 2.20 babies per woman in 1998 to 1.97 in 2008 and remains constant to the end of the projection period (low assumption).

The Northern Territory has the highest fertility rate of any State or Territory with considerably younger mothers than the rest of Australia. This is mainly a reflection of the high proportion of Indigenous women in the population whose fertility is much higher than that of non-Indigenous women.

Single year age-specific fertility rates were calculated by applying the 1996-1998 ratios of the Northern Territory to Australian age-specific fertility to high and low Australian fertility assumptions. The high assumption at the Australian level maintains a total fertility level of 1.75 babies per woman throughout the projection period, while the low assumption assumes fertility declines to 1.60 babies per woman by 2008 then remains constant to the end of the projection period.

Fertility assumptions for Darwin SD and Northern Territory-Bal SD were derived by adjusting the assumptions at the Northern Territory level for historical age-specific differentials. The total fertility rate in Darwin SD is 8% lower than the rate for the Northern Territory while the rate for Northern Territory-Bal SD is 8% to 10% higher. While the fertility rates change each year up to 2008, the relativity between Darwin SD and Northern Territory-Bal SD remains constant.

Fertility assumptions for SLAs were based on average age-specific fertility rates observed in each SLA between 1995 and 1999, projected to follow the assumed change at the Northern Territory level until 2008 and then remain constant to the end of the projection period.

C.2 Mortality
One assumption was made at the Northern Territory level. The assumption is that life expectancy at birth increases from the 1996-1998 level of 70.5 years for males and 75.4 years for females to 74.7 years for males and 78.5 years for females in 2021. It is based on the Australian average annual rate of improvement in life expectancy from 1986-1996 of 0.30 years per year for males and 0.22 years per year for females continuing from 1999 to 2003 and then gradually slowing.

The pattern of change in Australian age-sex-specific death rates from 1970-1972 to 1995-1997 has been assumed to continue for the projection period. This has been applied to base age-sex mortality rates taken from 1996-1998 Northern Territory life tables. Where the trend from 1970-1972 to 1995-1997 showed an increase in age-specific death rates (e.g. males aged 30-34 years), some arbitrary adjustment was performed to prevent the age-specific death rates from increasing in the future. Further adjustments were made to the assumed rates of change in age-specific death rates to conform to the predetermined life expectancies at birth for future years.

The mortality assumptions for Darwin SD and Northern Territory-Bal SD were based on the age-sex-specific assumptions for the Northern Territory, adjusted for differences in historical life expectancy. While the life expectancy at birth changes each year, the relativity between Darwin SD and Northern Territory-Bal SD remains constant.

The mortality assumptions for SLAs were based on the age-sex-specific assumed mortality rates for the Northern Territory, adjusted across all ages to provide consistency with the overall mortality experienced in each SLA between 1995 and 1999.

C.3 Overseas migration
Three assumptions were made at the Northern Territory level:
1 A net overseas migration gain of 938 people in 1999-2000, 844 in 2000-01 then an annual net gain of 721 from 2001-02 to the end of the projection period (high assumption).

2 A net overseas migration gain of 938 people in 1999-2000, 756 in 2000-01 then an annual net gain of 574 to the end of the projection period (medium assumption).

3 A net overseas migration gain of 938 people in 1999-2000, 687 in 2000-01 then an annual net gain of 429 to the end of the projection period (low assumption).

The net overseas migration component of population growth consists of three parts-permanent movement, long-term movement (for stays of 12 months or more) and category jumping. (Category jumping is the term used to describe changes between unintended and actual duration of stay of travellers to and from Australia, such that their classification as short-term or as long-term/permanent movers is different at arrival from that at departure.)

The assumed long-term levels of net overseas migration nationally were based on a 10-year moving average series of net overseas migration over the last 50 years. This average incorporates past fluctuations in net overseas migration and the associated influence of economic cycles. The Northern Territory's average share of net overseas migration for the three year period 1996-97 to 1998-99 was used as the basis for calculating the share going to the Northern Territory during the projection period. (Adjustments were made to the 1999-2000 and 2000-01 levels to smooth the transition from recent trends in net overseas migration to the longer term average.)

The proportion of migrants going to Darwin SD and Northern Territory-Bal SD was based on the average distribution of migrants arriving in 1990-91 and 1995-96, according to the 1991 and 1996 Censuses respectively. This distribution remains constant throughout the projection period.

The assumed age-sex structure of each migration component (i.e. permanent movement, long-term movement and category jumping) for the Northern Territory was based on the average structure from 1996-97 to 1998-99. However, the age-sex structure for net overseas migration varies during the projection period because the relative contribution of permanent and long-term components changes as long-term arrivals and departures increase from year to year.

Age-sex profiles at the part of Territory level were derived from the 1996 Census question on residence one year ago. Overseas departures were assumed to have the same age-sex distribution as overseas arrivals. These distributions were constrained to Northern Territory overseas arrivals and departures data for 1995-96.

C.4 Internal migration
Three assumptions were made at the Northern Territory level:
1 Net interstate migration increases from -600 in 1999-2000 to 1,500 in 2003-04 and remains constant to the end of the projection period (high assumption).

2 Net interstate migration increases from -600 in 1999-2000 to zero in 2002-03 and remains constant to the end of the projection period (medium assumption).

3 Net interstate migration decreases from -600 in 1999-2000 to -1,500 in 2003-04 and remains constant to the end of the projection period (low assumption).

Interstate migration is the most volatile component of population change for the Northern Territory and so it is an important determinant of the Northern Territory's population distribution.

While throughout the 1970s and early 1980s the Northern Territory experienced consistent small net annual gains, the late 1980s and early 1990s saw a series of net losses peaking at -3,100 in 1987-88. In the mid 1990s the Northern Territory experienced small net gains peaking at 1,800 in 1996-97. In the late 1990s this pattern was reversed and the preliminary estimates for 1999-2000 show a net loss of -900 people. (The interstate migration assumptions described above and below show a net loss of -600 people for 1999-2000. This is because the assumptions were developed before the preliminary estimate of -900 was available.)

Because of this volatility in net interstate migration flows, three long-term assumptions were made at the Northern Territory level after a transitional period from 1999-2000 to 2003-04. (Adjustments were made to the assumptions during this period to smooth the transition from recent trends in net interstate migration to the longer term average.) The medium assumption most closely reflects the long-term average net interstate migration experience of the Northern Territory, with more weight given to the past 10 years. The high and low assumptions reflect the volatility in the Northern Territory's interstate migration data and give a plausible broad range of projection outcomes, particularly in the short term.

The internal migration assumptions for Darwin SD and Northern Territory-Bal SD were based on historical trends. Historical net total migration to Darwin SD and Northern Territory-Bal SD was assumed to be the difference between population growth and natural increase in these regions. Net internal migration was assumed to be the difference between net total migration and net overseas migration.

C.5 Total migration
At the SLA level, the migration assumptions were developed based on total migration (i.e. overseas, interstate and inter-SLA migration combined), as this is the only migration data of reasonable quality which is available annually. For SLAs in Darwin SD, the migration assumptions were derived using historical net migration patterns, historical building approvals data, new dwelling projections from the Northern Territory Department of Lands, Planning and Environment, and trends in occupancy ratios. The range between high and low scenarios reflects different assumptions about the underlying migration for SLAs and their differing levels of new dwelling construction.

For SLAs in Northern Territory-Bal SD, the migration assumptions were derived using historical net migration patterns together with specific knowledge of likely future developments. The range between high and low scenarios is based on the observed variability in the net migration for each SLA between 1991 and 1999.

The age-sex profiles at the SLA level were based on overseas and inter-SLA migration rates used in the calculation of published ABS SLA age-sex population estimates, which were originally derived from the 1996 Census question which asks respondents to provide details of their usual address one year prior to Census night.

The SLA total migration assumptions were designed to sum to the high, medium and low migration assumptions for Darwin SD and Northern Territory-Bal SD. Similarly, SLA populations by single year of age and sex were constrained to sum to the respective Darwin SD or Northern Territory-Bal SD projected population.

D. Nature of projections
The nature of the projection method and inherent fluctuations in population dynamics mean that care should be taken when using and interpreting the projection results. The projections are not exact forecasts but simply illustrate future changes which would occur if the stated assumptions were to apply over the projection period.

In addition to the assumptions described above for fertility, mortality and overseas and internal migration, major future projects and developments in the Northern Territory which had been announced or were considered likely at the time the projections were developed were considered in the development of the projections. The projects and developments taken into consideration included: the Alice Springs to Darwin railway, development of oil and gas related industry in the Darwin region, and expansion of the Ord River irrigation scheme into the Northern Territory including agriculture and horticulture developments in the Douglas-Daly region.

The projections do not attempt to allow for non-demographic factors (eg. major government policy decisions, economic factors, catastrophes, wars) which may affect future demographic behaviour.

The unpredictability of migration trends, especially in the short-term, can have a significant effect on projection results. Special care should be taken with small SLAs (populations under 1,000 people) and small age-sex cells (populations under 100 people).

All SLAs in these projections are based on the Australian Standard Geographic Classification boundaries as they existed at 2001 Census (ASGC 2001). The actual boundaries for a given SLA, or for other geographic regions such as Local Government Areas (LGAs) derived from these SLAs, may change over time making the projections not comparable in the future with other data.

E. Liability
It is important to recognise that the projection results given in this report simply reflect the assumptions made about future fertility, mortality and migration trends. While the assumptions are formulated on the basis of an objective assessment of past demographic trends and their likely future dynamics, there can be no certainty that they will be realised.

No liability will be accepted by the Australian Bureau of Statistics for any damages arising from decisions or actions based upon these population projections.

F. Referencing these statistics
Source: Australian Bureau of Statistics. Population Projections, Northern Territory, 1999-2021 (ABS Cat. no. 3222.7).

G. Additional information
For further information on population projections refer to the ABS publication Population Projections, Australia, 1999 to 2101 (Cat. no. 3222.0) available from ABS offices in all capital cities. For more information, or quotes on the preparation of alternative projections, please contact:
Matthew Berger
Demography Section
Australian Bureau of Statistics
Tel. 02 6252 6639
Email: matthew.berger@abs.gov.au