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Feature Article - Interpreting Overseas Arrivals and Departures Statistics

The Australian Bureau of Statistics (ABS) adjusts short-term overseas arrivals and departures (OAD) statistics to account for calendar and irregular factors. The original, seasonally adjusted and trend series differ from each other in important respects, and these differences need to be understood so each series can be used effectively.

Original Estimates

Original estimates are the actual estimates the ABS derives from data provided by persons entering or leaving Australia. Movements in the original series can be attributed to the combined impact of systematic calendar related influences, irregular influences and the underlying (trend) direction in behaviour.

Systematic calendar related influences: These represent the combined effect of seasonal cycles, trading day patterns and moving holidays. Some examples of systematic calendar related influences include the large increase in travel during December as a result of the Christmas holiday period, or the increase in visitor arrivals from Singapore and Hong Kong during Chinese New Year (held in January or February).

Irregular influences: These are events or activities that are not systematic or predictable. They include the short-term phenomena that temporarily impact on OAD. Examples of such influences include: Dramatic fluctuations in the Australian dollar, war or terrorist attacks and special events (eg. Olympic Games or International Exhibitions) held in Australia.

Irregular influences also include sampling and non-sampling errors that behave erratically with no noticeable systematic pattern.

The underlying (trend) direction in behaviour: This results from such influences as population growth or general economic changes.

Seasonally adjusted time series

Seasonally adjusted time series estimates are derived by estimating and then removing systematic calendar related influences from the original series. This reveals the underlying non-seasonal features of a series. Therefore, this series represents the net effect of irregular influences and the underlying trend.

Trend Time Series

Trend estimates are derived by using the seasonally adjusted series and dampening any irregular influences. These estimates reveal the long term movement of the series without calendar related and irregular influences. Therefore, this series represents the underlying level of OAD, which helps analysts to determine whether short-term movements are increasing, decreasing or steadying.

Further information

For a more detailed discussion and analysis of OAD time series estimates, see the ABS Demography Working Paper 2004/2- Interpretaion and Use of Overseas Arrivals and Departures Estimates (cat.no.3106.0.55.002), available on the ABS website. This working paper explores time series concepts in more detail and uses the example, short term visitor arrivals to Australia from Japan to demonstrate the effect that calendar and irregular factors can have on original estimates.