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ABOUT THESE PROJECTIONS

INTRODUCTION

A summary of the method used to produce these projections is provided below. For more detailed information on the method, and how assumptions made about future fertility, mortality and overseas and internal migration were formulated, see Chapter 2—Assumptions of Population Projections, Australia 2004 to 2101 (cat. no. 3222.0).


METHOD

The Australian Bureau of Statistics (ABS) uses the cohort-component method for producing population projections. In this method, assumptions made about future levels of fertility, mortality, overseas migration and internal migration are applied to a base population (split by sex and single year of age) to obtain a projected population for the following year. The assumptions are then applied to this new (projected) population to obtain a projected population for the next year. This process is repeated until the end of the projection period is reached.

These projections span the period June 2004 to June 2101 for Australia, and June 2004 to June 2051 for the states, territories, capital cities and balances of state.

The base population for all geographic areas is the revised estimated resident population (ERP) at 30 June 2004.


WHICH PROJECTION SERIES TO USE

Future uncertainty, along with the subjective nature of assessing current trends, means that using a range of possible outcomes rather than a single projection series gives a more realistic view of the possible future size, distribution and age structure of Australia's population.

The ABS has produced 72 alternative projection series using different combinations of assumptions on fertility, mortality, overseas migration and interstate migration. Different series are appropriate for specific time horizons (shorter or longer term), the region being studied and any volatility in the components. All series can more or less accommodate possible future levels of fertility and mortality as both are fairly predictable. However, there is less certainty of future levels of overseas migration and interstate migration given their historical volatility. This volatility will occur over time due to future government policies and decision-making and economic, social and other determinants and influences.

Detailed information for the three main series (Series A, B and C in the table below) are provided in the following data cubes:

• Population Projections for Australia, 2004–2101—in SuperTABLE format,
• Population Projections by Capital City/Balance of State, 2004–2051—in SuperTABLE format, and
• Projected Population, Components of Change and Summary Statistics, for Australia, States and Territories, Capital City/Balance of State—in Microsoft Excel format.

• high assumption: the TFR will increase to 1.9 babies per woman by 2018, and remain constant thereafter;
• medium assumption: the TFR will decline to 1.7 babies per woman by 2018, and remain constant thereafter; and
• low assumption: the TFR will decline to 1.5 babies per woman by 2018, and remain constant thereafter.

• medium assumption: life expectancy at birth will reach 84.9 years for males and 88.0 years for females by 2050–51, and remain constant thereafter. Under this assumption life expectancy at birth will increase by 0.40 years per year for males and 0.30 years per year for females until 2005–06, then by 0.30 years per year for males and 0.25 years per year for females until 2010–11, after which mortality improvement will gradually decline until 2050–51; and
• high assumption: life expectancy at birth will reach 92.7 years for males and 95.1 years for females by 2050–51 and remain constant thereafter. Under this assumption male and female life expectancy at birth will increase by 0.40 years per year for males and 0.30 years per year for females until 2005–06, then by 0.30 years per year for males and 0.25 years per year for females until 2050–51.

• high assumption: annual NOM gain will increase to 140,000 people per year by 2007–08 and remain constant thereafter;
• medium assumption: annual NOM gain will be constant at 110,000 people per year throughout the projection period; and
• low assumption: annual NOM gain will decline to 80,000 people per year by 2007–08 and remain constant thereafter.

• high assumption: 'large' net population gains and losses for the states and territories;
• medium assumption: 'medium' net population gains and losses for the states and territories; and
• low assumption: 'small' net population gains and losses for the states and territories.

	HIGH LIFE EXPECTANCY AT BIRTH				MEDIUM LIFE EXPECTANCY AT BIRTH
	Net interstate migration (high)(a)	Net interstate migration (medium)	Net interstate migration (low)(a)		Net interstate migration (high)(a)	Net interstate migration (medium)	Net interstate migration (low)(a)
HIGH FERTILITY (TFR = 1.9)
Net overseas migration (per year)
140,000	1(A)	2	3		4	5	6
110,000	19	20	21		22	23	24
80,000	37	38	39		40	41	42
0	55	56	57		58	59	60
MEDIUM FERTILITY (TFR = 1.7)
Net overseas migration (per year)
140,000	7	8	9		10	11	12
110,000	25	26	27		28	29(B)	30
80,000	43	44	45		46	47	48
0	61	62	63		64	65	66
LOW FERTILITY (TFR = 1.5)
Net overseas migration (per year)
140,000	13	14	15		16	17	18
110,000	31	32	33		34	35	36
80,000	49	50	51		52	53	54(C)
0	67	68	69		70	71	72
(a) High and low interstate migration refer to high/low flow scenarios, and will therefore reflect high/low losses rather than high/low gains in some jurisdictions.