Bernard Salt's article "Come to your census in planning" (The Australian, 4 December 2008) does not convey an accurate description of the ABS population projections.
The ABS publishes a range (72) of population projections, not predictions or forecasts, to assist decision making about possible future population scenarios.
Australia's, and indeed Melbourne's future population size is by no means certain, and so the ABS projections are based on assumptions about future rates of fertility, internal and overseas migration and life expectancy. Population change is ultimately determined by actual social behaviour, health and lifestyle choices, economic conditions, policy implementation, and other factors over time, not by the ABS.
The choice of which assumptions to adopt at any point in time about future population growth is in the hands of the planner and developer - ABS simply provides a range of options for choice. Mr Salt has chosen only one for his article which happens to suit the purpose of his commentary.
Brian Pink
Australian Statistician
ABS response to "Come to your census in planning" (The Australian 4 December 2008)