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This report concludes that Medicare Australia data remains the best source for use in quarterly interstate migration estimates.
In accordance with legislative requirements, the ABS collects statistical information as is necessary to compile and publish quarterly population estimates for each state and territory. Estimates for the June quarter of each census year are calculated from the Australian Census of Population and Housing, whereas post-censal estimates for the other quarters are prepared by compiling the data for each of the components that make up the estimated resident population (ERP). Birth and death estimates are calculated using births and deaths registrations, while overseas migration is calculated using data collected from passenger cards, visas and passports at the border when a person enters or leaves Australia.
There are, however, no equivalent data sources that directly measure interstate migration. Due to this, in the past the ABS has used a number of indirect administrative data sources to estimate quarterly interstate migration, including electoral roll registrations, family allowance payments, and, most recently (for the period 2001-2006), Medicare registration data obtained from Medicare Australia. For the 2001-2006 period, Medicare data was also supplemented by Defence Force data to compensate for interstate movements of defence force personnel not in the Medicare change-of-address dataset.
Interstate migration is a key determinant of the accuracy of state and territory population estimates. It is the only component of the ERP that uses indirect data sources. The population estimates are generally highly accurate, with the average absolute intercensal error for 1996-2001 a low 0.55%. The accuracy of 2001-2006 interstate migration estimates will not be known until the intercensal error is calculated from the 2006 census data.
3. SUMMARY OF RESULTS
Medicare change of address data remains the best source available for calculating intercensal interstate migration estimates. The data source meets all criteria and is particularly valued for its timeliness and its extensive population coverage. This data source's strengths and weaknesses are discussed in more detail in section 5.
4. EVALUATION CRITERIA
The suitability of each prospective data source for use in the estimation of quarterly interstate migration for the period 2006-2011 is determined by its performance against a set of criteria: population and coverage, data content, geographic level, timeliness and periodicity, historical availability, consistency, and electronic capture. The criteria are broken down into ideal and minimum data characteristics as shown below.
Using these criteria to determine suitability for quarterly interstate migration estimates ensures that each data source is evaluated in a consistent and objective manner.
5. MEDICARE AUSTRALIA DATA
The Medicare Australia dataset includes personal details for all Australian usual residents excluding foreign diplomats and their families. In 2004, based on data provided to the ABS, the Medicare scheme had approximately 21 million clients enrolled collectively holding 12 million Medicare cards. People who reside in Australia (excluding Norfolk Island) are eligible for Medicare if they meet any of the following criteria:
There are also circumstances where people are granted temporary eligibility. Some of these categories include academics, employer nomination, skills transfer employees, and people in the various contributory parent visa category of Medicare.
The National Childhood Immunisation Register is a subset of the Medicare register which enhances the coverage of children.
There are however, some population groups that are not wholly represented by the Medicare database. These groups are mostly made up of those with access to alternative health services including defence force personnel, prisoners, persons eligible for the Department of Veterans Affairs Health Services, and Indigenous Australians. Recently, significant strategies have been put in place to enrol Indigenous Australians who would normally use an Aboriginal Medical Service.
Despite the under-representation of these population groups, the Medicare population of approximately 21 million (2004) is actually larger than the ABS' ERP (approximately 20.2 million at 31 December 2004) mainly because of its inclusion of defunct units such as deceased persons and card holders who no longer reside in Australia. However, these defunct units are kept to a minimum, with Medicare Australia checking their own records against state and territory death registrars as well as Department of Immigration and Multicultural Affairs (DIMA) settler files.
Data Capture and Upkeep
The Medicare registration database captures address information when a person either enrols for the first time or changes their enrolment details, for example when making a claim. Medicare relies upon people to advise them of any changes in enrolment details, including change of address, mostly though the Medicare branches. This is made more difficult with increases in bulk billing and electronic processing of claims. However, a number of agreements are currently being discussed in 2006 (for example with Australia Post) to send out forms to people who are known to have changed their address details requesting an update of information.
The Medicare Card Replacement Program also helps to keep members' details up to date. This program operates on a fluctuating five/seven year cycle and identifies those members whose cards are due to expire. Medicare then contacts these members, checking the addresses on the older cards against those listed in the telephone book. If the address is incorrect, a letter is sent to the last known address with a request for updated details.
Successive reviews in 1996 and 2001 have concluded that Medicare change of address data is the best administrative data source available for preparing quarterly estimates of interstate migration. The ABS currently uses Medicare postcode movements by age and sex for compiling interstate migration estimates.
Medicare data remains the best administrative source for use in the quarterly estimation of interstate migration. The ABS will also continue to supplement this data with Defence Force data to compensate for the interstate movements of defence force personnel not covered by Medicare.
6. TAXATION DATA
Income tax return data from the Australian Taxation Office (ATO) includes change of address details for all people (as well as their spouses/partners) who submit a tax return to the Australian government over two consecutive years. These data have potential to be valuable for estimating the numbers of working age movers (persons aged 15-64 years).
A 2006 evaluation conducted by the ABS found income tax return data to have two main limitations. The first is that the data are only available annually and therefore are not suitable for the ABS' production of quarterly estimates of interstate migration. The second main limitation found was that it did not meet the timeliness criterion. Substantial coverage of tax returns is only available 12 months after the end of the financial year, meaning that if the ABS was to use this data, estimates of interstate migration would be lagged by more than one year.
Taxation change of address data are not suitable for use as a data source for estimating quarterly interstate migration. In addition to the incomplete coverage, the data source's lack of timeliness makes it inappropriate for producing up-to-date estimates. Also, the data are only available annually making it an inappropriate source for quarterly estimates.
7. AUSTRALIA POST DATA
Australia Post offers an address redirection service to people who are moving anywhere within Australia or overseas. Commercial applications of the address-change database are managed by the First Direct Solutions (formerly Geospend) Division of Australia Post. The database distinguishes between permanent movers (those who use the service for a duration of one, three, six or 12 months) and temporary movers (those who select a date for the service to finish). The database also includes old and new address details, the date from which mail redirection should start and the name/s of the household member/s whose mail is to be redirected. It does not, however, contain age or sex details. Furthermore, although the database includes the date of commencement of redirection, this may not necessarily be the date of migration. The addresses can be CD-coded by Australia Post, and a database containing the origin and destination CD of each redirection application (but no person-identifiable information) can be purchased.
This database is potentially very useful for planners as it can be used to analyse and model mobility between small and user-defined geographical areas anywhere in Australia and over any period. Census data, which provide the same geographic options, are only available every five years and provide the location on census night, one year earlier and five years earlier.
However, the address change database is not a suitable data source for the ABS to use for interstate migration estimation because its coverage of the population of movers in Australia is incomplete. Possible factors that influence whether or not movers use the service include income, intended duration of migration, remoteness of origin or destination, whether or not all household members are moving, whether or not the mover already receives all of their mail at a Post Office Box that they can access from both their origin and destination address (e.g. near their place of employment), and whether or not the mover prefers to send out their own change of address advices. In addition, age or English literacy skill may influence which household members are nominated on the address redirection form.
A recent analysis conducted for a 3 month period in 2005 by the National Centre for Social Applications of Geographic Information Systems (GISCA) at the University of Adelaide found that, with the exception of the Northern Territory, each state and territory's share of all movements in the Australia Post database was reasonably similar to those estimated by the ABS. The direction of net migration was also consistent between the two data sources, i.e. a state with a net interstate migration gain in ABS estimates also showed a gain in the Australia Post data. However, the analysis also indicated that the Australia Post database's estimates of movers overall remained significantly lower than ABS estimates.
Australia Post change of address data are not suitable for use as a data source for quarterly interstate migration estimates. This is primarily due to the limited population coverage, with the database only covering those movers who use the redirection service. Data content is also unsuitable as the database does not include personal details such as sex, age/date of birth or the date of actual migration.
8. SCHOOL ENROLMENT DATA
School enrolment data are available through the ABS' National Schools Statistics Collection (NSSC). The NSSC is an annual by-product of the August Schools Census run by various government schools jurisdictions and the Department of Education, Science and Training (DEST). The collection includes student details such as single year of age, school year and state or territory for every enrolled student in Australia. Due to state and territory variations in compulsory school ages, the data could only provide consistent coverage for those students aged 6 to 14 years.
The NSSC data source is unsuitable for use in quarterly interstate migration estimates for two main reasons. Firstly, NSSC student details are only available in aggregate form rather than at the individual record level. Secondly, the data is only available annually, making it unsuitable for quarterly estimates.
NSSC school enrolment data remains an unsuitable source for use in quarterly interstate migration estimates. At present (2006), the data are only available in aggregate form. Data are also not available quarterly.
9. DRIVER LICENCE DATA
The National Exchange of Vehicle and Driver Information System (NEVDIS) is a national repository for driver licence data, which is updated by each state and territory vehicle licensing and registration department, except for Tasmania, which is expected to join by 2008. In 1999 and 2000 and again in 2006, the ABS investigated the possibility of using interstate transfer data from NEVDIS.
The main limitations of the NEVDIS database for interstate migration estimation purposes is that it does not record a previous address, only the current address of each licence-holder, and it does not include Tasmanian data. In addition, not all usual residents of Australia hold driver licences and the minimum age at which a licence may be obtained varies across the states and territories.
NEVDIS data are unsuitable as a data source for use in quarterly interstate migration estimates. This is primarily due to the fact that the database does not include a previous address for licence-holders. In addition, coverage is limited due to the exclusion of Tasmanian data and the fact that not every mover in Australia holds a driver licence.
10. AUSTRALIAN ELECTORAL ROLL DATA
The Australian Electoral Commission (AEC) maintains the Commonwealth electoral roll in accordance with joint roll arrangements with states and territories. Under these arrangements, elector details on the AEC's roll management system can be used by other electoral bodies to produce rolls for elections and by-elections. It means that electors need complete only one form to enrol for local government, state or territory and federal elections.
The AEC population endeavours to cover all people who are eligible to enrol to vote in Australian elections. A person is eligible to vote if he or she:
The extent of coverage of this sub-population has yet to be determined by the ABS, as has the extent to which interstate migration is promptly reflected in the electoral roll. This may be a problem if significant numbers of young adults or people who move wait until just before elections to update their details or enrol for the first time. In addition, people who are permanent residents but not Australian citizens are not eligible to enrol.
In the past, electoral roll data has been deemed unsuitable for use in quarterly estimates of interstate migration due to significant lags in updating electors' change of address details. Firstly, people tended not to update their address details until just before an election and secondly, the AEC only reviewed its electoral roll details every two years. However, in the last few years the AEC has implemented Continuous Roll Updating (CRU) through the use of targeted mail outs and fieldwork. Accordingly this data source may be much more useful for quarterly estimates of interstate migration than it was considered to be in the past.
The ABS has entered into discussions with the AEC with the aim of obtaining anonymous data that could be fully assessed to determine its usefulness. Some limited analysis of snapshots of anonymous data for six quarters from June 2000 indicated that there is some undercoverage of people aged 18 to 20 years old, and that there was significant undercoverage of interstate arrivals and departures. However, net interstate migration coincided reasonably closely with census and Medicare data for most states and territories. The ABS will endeavour to investigate this potential data source more thoroughly to better understand the extent and consistency of undercoverage before determining whether and how AEC data could be used in the quarterly estimation of interstate migration.
Electoral roll data has potential to be used in the quarterly estimation of interstate migration as a secondary validation source. The ABS will proceed with negotiations with the AEC aimed at obtaining anonymous electoral roll data and then thoroughly analysing the data to determine the extent to which it could be used.
11. ELECTRICITY CONNECTIONS DATA
In early 2006, in the search for a national database of electricity connections, the ABS obtained some information about the National Electricity Market Management Company Limited (NEMMCO) Market Settlement and Transfer Solution (MSATS) database.
NEMMCO was established in 1996 to administer and manage the National Electricity Market, which is a wholesale market for the supply of electricity to retailers and end-users in participating regions. With the progressive introduction of full retail competition in the electricity market, NEMMCO's role has extended to providing information technology systems to facilitate the transfer of customers between electricity retailers.
The MSATS database records all change requests and notifications in the electricity retail market, including the address of each connection point. However, the database is unsuitable for use in the quarterly estimation of interstate migration because it does not record changes of consumers' addresses. For example, if a person moves from one address to another and continues to use the same electricity retailer as the previous occupant of their new home, no record of the move appears on the MSATS database. In addition, in early 2006, the database only included all connection points in jurisdictions with full retail competition at the time (New South Wales, Victoria, South Australia and the Northern Territory). For the rest of Australia, a connection point is added to MSATS when the electricity retailer for that connection point is changed.
The NEMMCO MSATS database could also not be used for annual estimates of small area population as it is not possible to distinguish between dwellings and businesses, some connection points cover multiple dwellings, and the construction of a new dwelling does not necessarily lead to the creation of a new connection point on MSATS, e.g. if it is supplied from an existing electricity connection point.
The NEMMCO MSATS database is unsuitable as a data source for use in quarterly interstate migration estimates. The database currently only includes all connection points in some of the states and territories. It is not possible to distinguish between dwellings and businesses, and interstate migration moves are only recorded if they involve a change of electricity retailer.
12. DATA SOURCES EVALUATED IN 1996 AND 2001
The 2001 version of this report evaluated a number of other potential administrative data sources for use in quarterly interstate migration estimates that have not been included in the main section of this report because they have either been deemed unsuitable or because there have been no substantive changes in their potential for use. The latter data sources are listed below:
For the 2001 assessments of the above data sources see Demography Working Paper 2001/5 - Evaluation of Administrative Data Sources for Use in Quarterly Estimation of Internal Migration Between 2001 and 2006 (cat. no. 3127.0).
13. SUMMARY OF ALL EVALUATIONS
This table shows that Medicare data is the only administrative data source that meets every criterion for use in the estimation of quarterly interstate migration. The ABS will continue to use Medicare Australia data supplemented by Defence Force data for estimating quarterly interstate migration in the intercensal period 2006-2011.
Australian Bureau of Statistics 1999, Demography Working Paper 1996/1 - Evaluation of Administrative Data Sources for Use in Quarterly Estimation of Interstate Migration Between 1996 and 2001, (cat. no. 3109.0), ABS, Canberra.
Australian Bureau of Statistics 2001, Demography Working Paper 2001/5 - Evaluation of Administrative Data Sources for Use in Quarterly Estimation of Internal Migration Between 2001 and 2006, (cat. no. 3127.0), ABS, Canberra.
Australian Electoral Commission web site, viewed 30 August 2006, <http://www.aec.gov.au>.
Hugo, G., Harris, K., Bamford, E. and Nottage, J. 2005, Internal Migration in Australia - Analysis of Australia Post Mail Redirection Database March-May 2005 and Survey of Moving Households in Australia, April 2004-June 2005, unpublished, copies may be available from the Department of Transport and Regional Services (DOTARS) or the Victorian Department of Sustainability and Environment.
National Electricity Market Management Company (NEMMCO) June 2003, Retail Transfer Statistical Data (MSATS) - Specification, viewed 30 August 2006, <http://www.nemmco.com.au>.
NEMMCO 7 Jan 2005, Interpreting NEMMCO's Retail Transfer Statistical Data, viewed 30 August 2006, <http://www.nemmco.com.au>.
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