PRELIMINARY NOM ESTIMATES
6.46 Preliminary estimates using the improved method for estimating NOM were implemented in official ABS population estimates for September quarter 2006 and onwards with the release of the December quarter 2006 issue of Australian Demographic Statistics (cat. no. 3101.0).
6.47 Preliminary estimates of NOM are required 5 to 6 months after the reference quarter for the production of quarterly estimates of the population of Australia, states and territories. At that time, complete traveller histories for the 16 months following a reference quarter cannot be produced. Migration adjustments are calculated from changes in behaviour from final estimates two years earlier for the same groups of travellers. These migration adjustments are applied to travellers who are grouped according to age, sex, country of citizenship and state/territory, and account for differences between their intended duration of stay and their actual duration of stay.
6.48 Category of travel is determined by a number of dimensions:
- whether the traveller considers themselves to be a visitor or a resident
- the direction of travel (whether an arrival or a departure)
- the stated intended duration of stay or absence (for visitors arriving and residents departing)
- actual duration of stay or absence since the previous Australian border crossing (for visitors departing and residents returning).
6.49 Each traveller is then given an additive migration adjustment (MA) value which represents the difference between their initial contribution to NOM (+1, -1 or 0 as above) and their expected contribution to NOM if actual duration of stay could be determined. The MA value is derived during final estimation for the corresponding quarter two years previously, with an average MA value derived for each group of travellers. The group of travellers is defined by the cross-classification of category of travel by age by citizenship by state/territory. The average MA value is calculated within each group of travellers by summing their MA values and dividing by the number of travellers within the group. See Step 8 (in final estimates steps) for a definition of MA value. Each traveller in the current reference quarter (at preliminary estimation) receives the average MA value from its corresponding group of travellers two years previously. Preliminary NOM estimates for the reference quarter are then obtained by adding each traveller's MA value to their initial contribution to NOM, and aggregating to the desired level (such as state/territory).
6.50 In forming the cross-classified groups of travellers for which the average MA values are derived at final estimation (for later use in preliminary estimates), the following categories are used:
- category of travel has the 10 categories of travel listed earlier in this chapter
- state is divided into eight categories (New South Wales, Victoria, Queensland, South Australia, Western Australia, Tasmania, Northern Territory and the Australian Capital Territory). Other Territories (see paragraph 1.20 in Chapter 1 - Overview) are not included
- country of citizenship is divided into five groups:
- Australia including external territories
- New Zealand
- South-east and North-east Asia
- North-west Europe and North America
- age is divided into eight groups (0-4, 5-14, 15-19, 20-24, 25-34, 35-44, 45-54, 55+).
6.51 At present the preliminary estimation method does not provide assumptions of changes from State 1 to State 2. The method used for estimating preliminary NOM will be reviewed when a longer time series of estimates become available.