INTRODUCTION


Policy background
The potential of regional internal migration estimates
Population estimates and components of population change
Regional migration in context


The size, structure and distribution of Australia's population changes over time as a result of natural increase (births minus deaths) and people changing their place of usual residence through migration. Net migration, the difference between arrivals and departures, can be positive or negative.

For reasons such as source data availability, data requirements and demand, and for methodological reasons, the production and analysis of migration of Australian residents are generally considered based on three different movement types: overseas, interstate, and intrastate (or regional) migration.

Australia has long maintained a regular series of data on overseas and interstate migration, with a shorter time series available for internal migration.

Within Australia there is no direct quarterly measure of interstate migration, unlike that of natural increase and overseas migration. Instead, quarterly estimates of interstate migration are compiled by the ABS using a model based on Medicare change of address data, supplied by the Australian Government Department of Human Services, and Defence force personnel movements data, supplied by the Department of Defence. This model is reviewed and updated every five years using data from the latest Census of Population and Housing.

The Census also provides data on internal migration below state level. However, while the Census provides a good snapshot of intrastate (regional) migration every five years, more frequent and timely migration data would provide a better understanding of regional population change, and may possibly lead to preparing better quality estimates of regional populations.

Medicare data have not previously been deemed suitable for estimating internal migration below the state/territory level mainly because they are supplied to ABS by postcode, which is not directly compatible with the Australia's official statistical geography, the Australian Standard Geographical Classification (ASGC). The base spatial unit of the ASGC is the Statistical Local Area (SLA), which is the boundary set that the ABS has prepared estimates of population and its components. The ABS has invested considerable resources in recent years developing postcode to ASGC correspondences, based on estimated population distribution across postcodes. This discussion paper summarises a method to convert postcode-based internal migration data to ASGC boundaries using these correspondences, discusses challenges with this approach, and outlines potential solutions to these challenges. To illustrate the potential of the data, this paper presents an experimental version of these regional internal migration estimates.

The paper compares converted Medicare internal migration data for 2005-06 with internal migration data derived from the 2006 Census. This can provide an indication of the quality of the converted Medicare-based regional internal migration data. This comparison would aim to identify differences between the two datasets, which may also highlight issues or limitations with using the Medicare data converted to the SLA level.

The paper gives stakeholders an opportunity to provide feedback about the methodological issues associated with producing a regular series of regional internal migration estimates, which will be considered in the further development of these estimates.

From July 2011, the ABS commenced replacing the ASGC with the Australian Statistical Geography Standard (ASGS). The ASGS is designed to better meet user needs for social, demographic and economic statistics, and becomes the essential reference for understanding and interpreting the geographical context of ABS statistics (ABS, 2010c). Population estimates will be prepared based on this new geography from 2012 (ABS, 2011).

From 2012, the ABS will have access to Medicare data at the SA2 level, which is the spatial unit in the ASGS that broadly corresponds to the SLA. This will remove the quality issues associated with using postcode to ASGC correspondences in any further development of Medicare-based regional internal migration estimates.

Policy background

There has been ongoing interest in the population flows within Australia, which will become more critical for government policy makers and service planning as large regional or coastal centres continue to grow. It is useful for planners to understand the numbers and characteristics of people who are moving to these areas in order to better plan for the appropriate infrastructure and services that may be required.

The Sustainable Population Strategy for Australia (SEWPC, 2011) examines the likely impact of population change from the perspective of three key dimensions, including environmental sustainability, economic sustainability and sustainable communities. In light of the objectives of the strategy, there is a need for better data on regional population trends such as population mobility. The data would further inform planning and managing changes to the population.

Our Cities, Our Future - A national urban policy for a productive, sustainable and liveable future (DIT, 2011) outlines the Australian Government's objectives and directions for its cities in preparation for the decades ahead. The National Urban Policy, which establishes the first long-term national framework to guide policy development and public and private investment in cities, sets a vision for Australian cities to deliver future prosperity and wellbeing for its communities. While focusing on capital cities, the policy recognises the important role that major regional centres also play, and the substantial challenges that they face in dealing with the complexities of the modern economy.

Regional programs may benefit from a series of regional internal migration estimates, for example, the regional programs outlined by the Department of Regional Australia, Regional Development and Local Government <http://www.regional.gov.au>, established in September 2010. The 2011-12 Budget committed $4.3 billion to areas including transport, water, energy, health, education, and communication infrastructure for regional Australia.

The potential of regional internal migration estimates

There are many reasons why people may move between regions, including employment or educational opportunities, retirement from employment, moving into a retirement village or nursing home, health-related reasons, destination-related (e.g. "sea change" or "tree change"), adult children moving out of home, building a home in a new development and family-related reasons. The characteristics of people living within a region may also determine their likelihood to stay within the same region, for example, young adults tend to be more mobile.

Potentially, a new series of regular regional internal migration estimates would provide better information on movement patterns of Australia's population at a regional level and fill an information gap in Australia's demographic data series. There are many aspects of internal migration that could be analysed much further if a more regular and timely series of regional migration data were available, including:

• How inflows and outflows for particular regions vary over time;
• Whether certain regions have particularly large or small volumes of movers;
• Where people come from when they move to coastal areas;
• How far people move;
• Whether some regions are more attractive to younger or older people;
• Whether some regions attract more males than females, or vice versa.

Population estimates and components of population change

In accordance with legislative requirements, the ABS provides quarterly estimates of the population of Australia and each of the states and territories.

Once every five years, the Census of Population and Housing provides the base for calculating population estimates. Population estimates for Australia and the states and territories are updated by adding to the estimated population the components of natural increase (births minus deaths) and net overseas migration. For the states and territories, account is also taken of estimated interstate migration.

Overseas migration is calculated using data collected from passenger cards, visas and passports for those persons travelling into and out of Australia. Data on interstate migration, however, are not directly estimated. This is because there is no specific centralised requirement for a person who changes their state or territory of usual residence to register their move for statistical purposes. Interstate migration is estimated using a model based on Medicare and Defence administrative by-product data.

To estimate population below the state level, the ABS relies on a regression model to estimate regional population change since the previous Census using SLAs as the base geographic level. The regression model uses change in population indicator data to estimate total population change, i.e. to estimate the combined effect of natural increase and internal migration at the regional level. The ABS uses this approach to estimate regional population due to difficulties in preparing reliable, regular and timely estimates of internal migration below state level (ABS 2009a). From 2012 these estimates will be prepared based on SA2s.

Regional migration in context

Despite Australia having a long-established series on numbers of interstate moves, migration between states and territories constitutes a small proportion of total moves within Australia.

The 2006 Census recorded that 2.81 million people changed their place of usual residence in the previous year, with just 10.1 per cent (283,500 people) moving between states/territories.

In the 2006 Census, 1.78 million people reported that they resided in a different SLA one year previously. The vast majority (84.1%) of these people moved between different SLAs within the same state/territory.