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INTERSTATE MIGRATION METHOD REVIEWED


Estimates of interstate migration are modelled using Medicare data on change of address. This model is reviewed and updated every five years using data from the latest Census of Population and Housing, including change of address data and final rebased population estimates for the intercensal period. Changes to the model with updated expansion factors have now been applied to interstate migration estimates from September quarter 2006 onwards and will include the revision of preliminary estimates already published. These estimates will be released on the 18 March 2009 in Australian Demographic Statistics, Sep 2008 (cat. no. 3101.0).

The outcome of the review on the migration model is essentially the same as the previous model used to estimate interstate migration for 2001 to 2006. It includes updated expansion factors that have been calculated using the latest data available, including Census change of address data and additional Medicare data used to help measure multiple movers (people who may have moved more than once during the year prior to the 2006 Census). Expansion factors are used to account for an under coverage of Medicare data by various ages and sex. The model includes the following characteristics:

• Medicare data lagged by three months (both for calculating expansion factors and for estimating progressive quarters of interstate migration);
• smoothed inputs used to produce expansion factors (ie: Census, Medicare & multiple movers data were smoothed);
• capping applied to expansion factors (in contrast to the 2001-06 method);
• expansion factors applied to males aged 17 to 30 years and females aged 17 to 25 (this differs to the age range used in the 2001-06 method);
• no smoothing applied to the expansion factors.