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Appendix 2: DATA AND METHODOLOGICAL LIMITATIONS

Geography

In this article, Census data are analysed and presented at the Local Government Area (LGA) geographical level based on the Australian Standard Geographical Classification (ASGC) boundaries as at 2006. Data from the 2001 Census has been transformed to ASGC 2006 boundaries. For more information about Local Government Areas, see Statistical Geography Volume 1 - Australian Standard Geographic Classification (ASGC), 2006 (cat. no. 1216.0).

Local Government Areas vary considerably in size and population. For this reason, population turnover rates are expressed relative to the 2001 Census count, adjusted to build comparability between the 2001 and 2006 Census populations. In this article, a rate per 1,000 population is used.

Table 1 shows the number of LGAs in each state by the size of their Estimated Resident Population (ERP) as at 30 June 2006. The ERP and land area of LGAs varies significantly between and within each state and territory. For example, Murchison (S), a rural LGA in Western Australia, had an ERP of only 141 people in 2006 and a land area of 44 909.7km². Yet Stirling (C), an LGA encompassing suburban areas of Perth, had a 2006 ERP of 183 897 people and a land area of 105.1km².

	ERP < 1 000 No. of LGAs	ERP 1 000 - 4 999 No. of LGAs	ERP 5 000 - 9 999 No. of LGAs	ERP 10 000 - 49 999 No. of LGAs	ERP 50 000 - 99 999 No. of LGAs	ERP 100 000 - 200 000 No. of LGAs	ERP > 200 000 No. of LGAs	Total LGAs No.
New South Wales	0	26	26	53	26	19	2	152
Victoria	0	2	8	32	15	20	2	79
Queensland	38	51	19	32	8	8	2	158
South Australia	2	24	10	25	4	5	0	70
Western Australia	40	47	14	28	10	3	0	142
Tasmania	1	5	8	13	2	0	0	29
Northern Territory	25	7	1	3	1	0	0	37
Total	106	162	86	186	66	55	6	667

Census counts and population estimates

All data used in this article is from the 2001 and 2006 Censuses of Population and Housing. Census data has certain limitations and some adjustments have been made to the Census counts used in this article. These are explained in more detail in the following paragraphs.

Data presented in this publication are based on the concept of 'Usual residence'. This refers to the place where people usually lived or intended to live for a period of six months or more in 2006. All visitors to a dwelling have been excluded (as they are counted at their own Usual residence). Overseas visitors are also excluded from the usual residence data.

Data presented in this publication may differ from the data in Census tables on the ABS website due to randomisation of numbers. For further information refer to Introduced Random Error. see 2901.0 - Census Dictionary, 2006.

Analysis presented in this article is based upon data from both the 2001 and 2006 Censuses. Data from the 2006 Census has been used in calculating the growth rate of the population, and in calculating population flows. Data from the 2001 Census has been used in calculating the growth rate of the population, and in calculating the turnover relative to the size of each LGA.

The 2006 Census has three questions on usual residence that ask where the person usually lives on Census Night, and where the person usually lived one year ago and five years ago. The information acquired from the answers to the usual residence questions is recorded in the usual residence indicator variables: Usual Address Indicator Census Night (UAICP), Usual Address One Year Ago Indicator (UAI1P), Usual Address Five Years Ago Indicator (UAI5P). The analysis undertaken in this article could have been based upon place of residence one year ago, however five years was chosen in order to calculate population counts as at the five yearly Census in order to calculate growth rates over the same period. Using place of usual residence one year ago would have likely produced different results (potentially lower turnover rates, as fewer people would move in a one year period than in a five year period). Use of usual residence indicators, in conjunction with other variables relating to usual residence, make it possible to identify the pattern of gross and net movement of people between three dates, i.e. Census Night, one year ago and five years ago. The following usual residence variables are available: Place of Usual Residence (PURP), Place of Usual Residence One Year Ago (PUR1P), Place of Usual Residence Five Years Ago (PUR5P), see Census Dictionary, 2006 (cat. no. 2901.0). Not all people answer the questions in the Census about where they lived once year ago or five years ago. In the 2006 Census, 7% of respondents did not answer this question.

Growth and turnover rates

Average annual growth rate in usual resident population between the 2001 and 2006 Census is calculated as a percentage using the formula below, where P₀ is the population at the start of the period, P_n is the population at the end of the period and n is the length of the period between P₀ and P_n in years.

[(P_n/P₀)^1/n-1] x 100

Population flow is the gross (total) movement into and out of a region. Population flow is defined as the gross movement of people into and out of the region between the 2001 and 2006 Census, expressed in the following formula:

Population Flow = Arrivals + Departures where

Arrivals were calculated using the series of questions on the 2006 Census form relating to where a person usually lives (on Census Night) and lived five years ago. These questions were used to determine the number of people who lived at a different usual address (to their current LGA) within Australia or lived overseas five years ago. Persons aged 0-4 years at the 2006 Census and 'not stated' addresses, where a person did not answer any component of where they lived five years ago, and people who recorded that they lived elsewhere in Australia five years ago but only partially stated their address, eg. a city, were excluded from this calculation. People who lived overseas five years ago were included.

Departures were calculated using the series of questions on the 2006 Census form relating to where a person usually lives (on Census Night) and lived five years ago. These questions were used to determine the number of people usually resident in Australia who no longer lived in the same LGA in Australia that they lived in five years ago. Excluded were: people who recorded their address five years ago as 'undefined state' and 'undefined city' as it is impossible to identify the LGA these people were and therefore it is not possible to report if or where they have departed; persons aged 0-4 years at the 2006 Census; people who did not state their place of usual residence five years ago i.e. 'not stated'; overseas visitors; and residents temporarily overseas at the time of the 2006 Census.

Population Turnover = Population Flow / Modified 2001 Census count

The Modified Census count for 2001 used in the calculation of turnover excludes those persons who, at the 2006 Census, were aged 0-4 or who did not state where they lived five years ago. This is consistent with the calculation of arrivals and departures. This Modified count is different from that used in the column '2001 Census count' also used in this article and which also appears in the tables in this publication.

The modified 2001 census count is calculated as outlined in the following formula;

Modified 2001 Census count = 2001 Census count LESS the number of who were aged 0-4 in 2006, LESS the number of people who in 2006 did not state where they lived five years ago.

The official population measure produced by the Australian Bureau of Statistics is Estimated Resident Population, not Census counts. See 2006 Census of Population and Housing - Fact Sheets, 2006 (cat. no. 2914.0). For further information on the 2006 Census of Population and Housing, see Census Data Quality Statement.

A note of caution

The Census asks people where they usually lived one year and five years prior to the Census date. This information can be compared with place of usual residence on Census night to examine internal migration patterns within Australia. There are some limitations in using Census data to determine patterns of internal migration. Movements of people within Australia could only be determined for those who were counted in the 2006 Census and stated a place of usual residence in Australia in 2001. People who made multiple moves between these periods would only be counted as moving once (or not at all if they moved back to where they came from).

Additionally, 7% of the 2006 Census population aged five years and over did not state their usual residence five years ago. These people have been excluded from this analysis, and therefore the arrival and departures numbers will under count the actual number of people who moved between regions in the five year period between censuses.

The strength of the Census data is that it enables the construction of small area estimates, such as at the LGA level, but this strength does come at a cost. In this case the cost relates to the necessary adoption of different conceptual bases than would be used to create official estimates within the ERP conceptual framework. The main conceptual differences regarding scope are that the Census-based population turnover estimates released in this publication exclude people who are included in the ERP numbers, namely: people under 5 years old at the time of the 2006 Census; residents temporarily overseas; and Census undercount.

In addition to these scope differences, the Census-based population turnover estimates released in this publication have been constructed using information relating only to those people who stated where they lived five years ago when they completed the 2006 Census questionnaire (i.e. migration status has not been imputed for people who did not state where they lived five years ago when they completed the 2006 Census questionnaire).

Finally, the estimates regarding people departing from an LGA exclude any information about people who (at the time of the 2006 Census) no longer lived in Australia. This is because these people are not enumerated as part of the Census.

As a result, users need to be aware that all of these estimates contain biases of varying extent (for example, in that they do not contain information about the characteristics of those who did not state where they lived five years ago) and that this degree of bias needs to be taken into account when thinking through the possible implications of these estimates for an LGA of interest.