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4 A number of characteristics collected about travellers are also available in this release. For more information and a complete list of variables available see Explanatory Notes paragraphs 35 and 37.
SOURCE OF THE STATISTICS
5 Administrative information on persons arriving in, or departing from, Australia is collected via various processing systems, passport documents, visa information, and incoming and outgoing passenger cards (see Appendix 1). Incoming persons provide information in visa applications except those travelling as Australian or New Zealand citizens. These administrative data are collected by the Australian Government Department of Immigration and Border Protection (DIBP) under the authority of the Migration Regulations (Migration Act, 1958).
6 ABS statistics on overseas arrivals and departures (OAD) are compiled using information from DIBP sources. Overseas movements are collected and matched (where possible) by DIBP and then stored with movement records on the Travel and Immigration Processing System (TRIPS). Each month the matched OAD movement records are supplied to the ABS and then processed. From October 2014, due to an increase in missing passenger cards, both matched and unmatched OAD movement records are now supplied to the ABS for processing within the OAD system.
7 Overseas arrivals and departures statistics relate to all recorded movements of travellers who cross Australia's international border. The statistics record the number of movements of travellers rather than the number of travellers (i.e. multiple movements of an individual traveller during a given reference period are each counted separately). It includes the movements of all travellers regardless of their nationality, citizenship or legal status.
8 The statistics exclude the movements of operational air and ships' crew, of transit passengers who pass through Australia but are not cleared for entry (including some defence force personnel), and of passengers on pleasure cruises commencing and finishing in Australia. These statistics also exclude undocumented arrivals or departures.
ESTIMATION SAMPLING METHOD
9 OAD statistics are derived from a combination of full enumeration and sampling. All permanent movements and all movements with a duration of stay of one year or more are fully enumerated. The number of movements where the duration of stay is less than one year are fully enumerated, however their characteristics are sampled. From January 2005, about 5% of all short-term movements have been selected for sample. Statistics relating to these movements are therefore estimates which may differ from statistics which would have been obtained if details of all these movements had been processed. Sample standard errors can be found under Standard Errors in the Explanatory Notes tab of this release.
CORRECTIONS AND IMPUTATIONS
10 The imprecision due to sampling errors should not be confused with errors arising from imperfections in reporting, which may occur in any data collection, whether sampled or not. Every effort is made to minimise such errors, both through careful design of the passenger cards and through checks on the information once it is received. During the edit process some items are corrected where they conflict with other known information. For some missing information such as category of movement, country of residence/stay, duration of stay, passenger card box type, and state of stay additional sources of data are used. These include tracking an individual's most recent known future movement (movement after their reference movement), or historical movement (movement before their reference movement), and flight information to ascertain an individuals country of embarkation or disembarkation. Any remaining information that is missing is imputed for the following records: age, category of movement, country of birth, country of embarkation/disembarkation, country of residence/stay, duration of stay, passenger card box type, reason for journey, sex and state of stay. These are imputed using information that is available for other similar records (known as hot deck imputation). More information is available in the Data Quality Issues (Appendix 2) in the Explanatory Notes section of this release.
11 Errors of this kind differ from discrepancies arising from the fact that certain information reflects the travellers' intentions at the time the passenger cards were completed. These intentions are, of course, subject to change. Particularly affected is the distinction between permanent and temporary movement and in the latter case, duration of intended stay, country in which most time will be spent and main reason for journey.
REBUILD OF THE OAD SYSTEM AND BREAK IN SERIES
12 In 2013, the ABS completed a rebuild of the system which creates OAD data. The primary aim of this project was to improve the quality of OAD data, given its importance as an input to a broad range of statistical outputs. The new system has been thoroughly tested by processing over ten years of data. Imputations for missing traveller data have been improved, in particular the duration of stay and the country of birth variables. Detailed information on the changes and improvements arising from the rebuild of the OAD system appears in the Data Quality Issues (Appendix 2) in the Explanatory Notes section of this release.
13 The rebuild of the system has resulted in a break in series, necessitating a revised time series for OAD data based on the improved methodology from July 2004 to December 2013. The break in series is from July 2004.
14 The classification of countries in this release is the Standard Australian Classification of Countries, 2011, Version 2.3. For more detailed information, refer to the ABS release Standard Australian Classification of Countries (SACC), 2011 (cat. no. 1269.0) or the Country Classification excel spreadsheet in the Downloads tab of this release. The entire times series has been backcast using this version of the classification.
15 The statistics on country of residence or main destination, and country of embarkation or disembarkation have certain limitations because of reporting on passenger cards. For example many travellers just list the UK on their passenger card, thus England, Scotland, Wales, Northern Ireland, Guernsey, Jersey and the Isle of Man are often combined to be the United Kingdom, Channel Islands and Isle of Man (UK, CI & IOM).
STATE AND TERRITORY CLASSIFICATION
16 Following the 1992 amendment to the Acts Interpretation Act to include the Indian Ocean Territories of Christmas Island and the Cocos (Keeling) Islands as part of geographic Australia, population estimates commencing with September quarter 1993 include estimates for these two territories. To reflect this change, another category of the state and territory classification has been created, known as Other Territories. Other Territories includes Jervis Bay Territory, Christmas Island and the Cocos (Keeling) Islands. OAD data for Other Territories are not available prior to February 1995.
SEASONAL ADJUSTMENT AND TREND ESTIMATES
17 Seasonally adjusted and trend estimates of short-term overseas movements are shown in tables 1, 2, 3, 4, 7 and 8.
18 Seasonally adjusted estimates are derived by estimating and removing systematic calendar related effects from the original series. In the short-term visitor arrival and short-term resident departure series, these calendar related effects are known as seasonal (e.g. increased travel in December due to the Christmas holiday period) and trading day influences (arising from the varying length of each month and the varying number of Sundays, Mondays, Tuesdays, etc. in each month). Each influence is estimated by separate seasonal and trading day factors which, when combined, are referred to as the combined adjustment factors.
19 From November 2004, ABS has introduced an improved method for removing trading day effects from seasonally adjusted estimates. Corrections for trading day effects are now applied as prior corrections to the original estimates, rather than being applied within the seasonal adjustment process. This is now consistent with the treatment of any corrections for large extremes, changes in level, changes in seasonal pattern, Easter, and other effects. This change in methodology has resulted in revisions to seasonally adjusted and trend estimates.
20 From July 2003, concurrent seasonal adjustment methodology has been used to derive the combined adjustment factors. This means that data from the current month are used in estimating seasonal and trading day factors for the current and previous months. Concurrent seasonal adjustment replaces the forward factor methodology used since seasonal adjustment of short-term visitor arrivals began in 1969 and short-term resident departures in 1976.
21 Concurrent adjustment can result in revisions each month to the seasonally adjusted estimates for earlier periods. However, in most instances, the only noticeable revisions will be to the combined adjustment factors for the current month, the previous month and the same month a year ago. Although there is no specific information paper on concurrent adjustment to short-term visitor arrivals or resident departures, more detail on the method in general can be found in the Information Paper: Introduction of Concurrent Seasonal Adjustment into the Retail Trade Series (cat. no. 8514.0).
22 The ABS implemented improved methods of producing seasonally adjusted estimates from July 2007, focussing on the application of Auto-regressive Integrated Moving Average (ARIMA) modelling techniques, which can improve the revision properties of the seasonally adjusted and trend estimates. For more information on the details of ARIMA modelling see 'Feature article: Use of ARIMA modelling to reduce revisions' in the October 2004 issue of Australian Economic Indicators (cat. no. 1350.0).
23 Seasonal adjustment procedures do not aim to remove the irregular or non-seasonal influences which may be present in any particular month, such as the effect of major sporting and cultural events, changes in airfares and the fluctuation of the Australian dollar relative to other currencies. Irregular influences that are highly volatile can make it difficult to interpret the movement of the series even after adjustment for seasonal variation. Trend estimates take these irregular influences into account.
24 The trend estimates of short-term overseas visitor arrivals and short-term Australian resident departures are derived by applying a 13-term Henderson weighted moving average to all months of the respective seasonally adjusted series except the first and last six months.
25 While this technique enables smoothed data for the latest period to be produced, it does result in revisions to the smoothed series, principally of recent months, as additional observations become available. There may also be revisions as a result of the re-estimation of the seasonal factors. For further information, see A Guide to Interpreting Time Series - Monitoring Trends (cat. no. 1349.0) and Time Series Analysis Frequently Asked Questions, 2003 (cat. no. 1346.0.55.002).
26 Occasionally situations occur that necessitate breaks being applied to the trend series. These breaks are necessary because of a change in the underlying level of the series. While the breaks apply to an individual country (e.g. Indonesia) a consequence is that breaks are also applied to the regional total series (e.g. Total South-East Asia) and the total series. Breaks currently included in the trend series are as follows:
27 An improved correction method has been implemented in the seasonal adjustment process to remove the effects of Chinese New Year, Ramadan, Diwali and Easter from the seasonally adjusted estimates.
Biennial seasonal adjustment reanalysis
28 The seasonally adjusted and trend series have been updated following the biennial review of the seasonal adjustment process with the release of the April 2016 issue. This review confirms the extent to which movements are affected by seasonal or irregular influences. As a result, the seasonally adjusted and trend estimates of a number of series have been revised.
29 Unreliable seasonal adjustment: In using the seasonally adjusted series, care should be exercised because of the difficulties associated with reliably estimating the seasonal pattern for the following short-term resident departure series: Other North-East Asia and United Arab Emirates. These series will be revised during the next biennial seasonal adjustment reanalyses.
Effect of new seasonally adjusted estimates on trend estimates
30 Under concurrent seasonal adjustment, the most recent seasonally adjusted and trend estimates are likely to be revised when estimates for subsequent months become available. The trend revision is a combined result of the revision of the seasonally adjusted estimates and the revision derived from the use of asymmetric moving averages as future data become available. ABS research shows that about 75% of the total revision to the trend estimate is due to the use of different asymmetric moving averages when the estimate for the next time period becomes available. To assess the reliability of the trend estimate, the 'what-if' charts (displayed in the Main Features section) present trend estimates under two different scenarios for the next time period. The charts show only the impact due to the changes of the asymmetric moving averages and do not include the unknown impact of revision to seasonal factor estimates that would arise when the estimate for the next time period becomes available.
31 For a detailed discussion and analysis of OAD time series estimates, see the ABS Demography Working Paper 2004/2 - Interpretation and Use of Overseas Arrivals and Departures Estimates (cat. no. 3106.0.55.002).
32 The Census and Statistics Act, 1905 provides the authority for the ABS to collect statistical information, and requires that statistical output shall not be published or disseminated in a manner that is likely to enable the identification of a particular person or organisation. This requirement means that the ABS must take care and make assurances that any statistical information about individual respondents cannot be derived from published data.
33 Some techniques used to guard against identification or disclosure of confidential information in statistical tables are suppression of sensitive cells, random adjustments to cells with very small values and rounding. In these cases data may not sum to totals due to the confidentialisation of individual cells.
34 The statistics in this release have been rounded to the nearest 100 for short-term movements and to the nearest 10 for permanent and long-term movements. Where figures have been rounded, discrepancies may occur between sums of component items and totals. Analysis featured in the Key Points and Main Features of this release is based on un-rounded data. Calculations made on rounded data may differ to those published.
ADDITIONAL STATISTICS AVAILABLE
36 To minimise the risk of identifying individuals in aggregate statistics, a technique is used to randomly adjust cell values. This technique is called perturbation. Perturbation involves small random adjustment of the statistics and is considered the most satisfactory technique for avoiding the release of identifiable statistics while maximising the range of information that can be released. These adjustments have a negligible impact on the underlying pattern of the statistics. After perturbation, a given published cell value will be consistent across all tables. However, adding up cell values to derive a total will not necessarily give the same result as published totals.
37 The following variables for overseas arrivals and departures data are available on request.
38 Related statistics are also published by:
39 As well as the statistics included in this and related releases, additional demographic information is available on the ABS website. Users can access the full range of electronic ABS data free of charge on the ABS website.
40 The ABS also issues a daily Release Advice on the website which details the products to be released in the week ahead.
41 This release draws extensively on information provided by the Australian Government Department of Immigration and Border Protection (DIBP). The ABS also uses information provided freely by individuals, businesses, governments and other organisations. Their continued cooperation is very much appreciated; without it, the wide range of statistics published by the ABS would not be available. Information received by the ABS is treated in strict confidence as required by the Census and Statistics Act 1905.
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