At each Census, Collection Districts may be redesigned to accommodate growth in population or to conform to other administrative data. To assist users to compare data for Collection Districts which changed between the 2001 and 2006 Censuses, a comparability code has been allocated to pairs of 2001 and 2006 Collection Districts. The resultant listing, which includes all Collection Districts for both 2001 and 2006, indicates the degree to which the boundary of a Collection District has changed between the 2001 and 2006 Censuses. The data is supplied as a comma delimited text file with an accompanying explanation of the meaning of each code.


Further information may be obtained by contacting Geographic Classification, email geography@abs.gov.au or by writing to Locked Bag 10, Belconnen, ACT 2616.


Record Structure:

Field Name	Type	Description
CDCODE_2006	Character	ASGC 2006 Collection District code.
CHANGE_CODE_2006	Character	Change code.
CDCODE_2001	Character	ASGC 2001 Collection District code.

Collection District code:

The 2001 to 2006 Census Collection District Comparability file includes a record for every 2001 and 2006 CD. Where there is an intersection between two CD boundaries (i.e. where a comparison between a 2001 CD and a 2006 CD can be made) there is a CD code for both Census years. Where a 2001 CD has been removed or a new 2006 CD created the relevant CD code is listed as "0".

Example:

"CDCODE_2006", "CHANGE_CODE_2006", "CDCODE_2001"
0, 6 , 4150211 (note: 2001 CD code not used in 2006)
4010101, 1 , 4010101
4010102, 0 , 4010102
4010103, 9 , 4010103

Change Code:

Comparability Codes are assigned a number between 0 - 9. They indicate the following:

Field	Explanation
0	2006 CD is perfectly comparable to the 2001 CD.
1	Although a change to the CD boundary has occurred, there is no change to population and dwellings.
2	CD is comparable within a 2% dwelling limit. That is a boundary change has occurred, however, no more than 2% of the 2001 dwellings in the CD have been subtracted from or added to the CD.
3	CD is comparable within a 10% dwelling limit. That is a boundary change has occurred, however, no more than 10% of the 2001 dwellings in the CD have been subtracted from or added to the CD.
4	CD is not comparable due to a split into two parts (the 2001 boundary being retained around the two new 2006 CDs).
5	As for 4 above except that the split has involved the creation of three or more new CDs.
6	CD is not comparable due to the extent of boundary variation.
7	CD is not comparable because it is an amalgamation of two 2001 CDs to give a new 2006 CD (the 2001 outer boundaries are retained).
8	CD is not comparable due to an amalgamation of three or more 2001 CDs, retaining the same outer boundaries.
9	The 2006 CD has changed slightly when compared with the 2001 CD due to the supply of new basemap. The CD boundary follows the same features, however, due to the new basemap the boundary has been re-aligned accordingly.

Calculating Change Codes

When an adjustment has been made to CD boundaries during the course of CD Design we need to calculate that change code in order to give users an indication of how comparable a CD is between Census years. To do this we use a formula whereby the number of dwellings from the previous Census (and boundary) are compared to the number of dwellings that the newly adjusted boundary would have contained had the boundary been the boundary used in 2001. This is calculated as a percentage and the resulting percentage determines the change code allocated for a particular CD.

For example in 2001 CDs 1421003 and 1421004 are shown below as they were when the 2001 Census was conducted.

Figure (a)
In 2001 CD 1421003 contained 142 dwellings while CD 1421004 contained 304 dwellings. During the course of redesigning CDs for the 2006 Census it was decided that these two CDs were to be modified and they were adjusted as shown below.

Figure (b)


As can be seen in Figure (b) part of CD 1421004 has been "donated" to CD 1421003. As a result of this boundary change we need to calculate the change code.

The change code is calculated by determining the number of dwellings these CDs would have contained had they looked like Figure (b) in 2001 (known as adjusted dwellings) compared with the number of dwellings they actually contained in their original form as shown in Figure (a). The absolute value difference of the 2 dwelling counts is then divided by the actual dwelling count, which is then multiplied by 100 to provide us with a value in percentage terms. This percentage change determines the change code for the CD.

CD 1421003 adjusted dwellings count is 160 (the number of dwellings it would have contained if it looked like the boundary in Figure (b) in 2001). It's actual dwelling count in 2001 was 142 (the number of dwellings it had based on the boundary contained in Figure (a)). The absolute difference is 18. This figure is then divided by the actual dwelling count which is 142 and multiplied by 100 to give us a percentage change of 12.7%. Due to this CD having a change of 12.7% it would be allocated a change code of 6 as the change is greater than 10% thus indicating that the CD is not comparable.

CD 1421004 had an actual dwelling count of 304 dwellings. This is the number of dwellings it contained based on it's 2001 shape as shown in Figure (a). It's adjusted dwelling count is 286, which is the number of dwellings it would have contained if it looked the boundary in Figure (b) in 2001. The absolute difference between the actual dwelling count and the adjusted dwelling count is 18. This figure is then divided by the actual dwelling count which was 304 and multiplied by 100 to give us it's percentage change. In this case the percentage change is 5.9%. Based on this percentage the change code allocated would be a 3 indicating that the change is between 2% and 10% meaning that there is some level of comparability between Census years.

This formula is used in all cases where boundary adjustment has occurred and will result in CDs being allocated a change code of 1, 2, 3 or 6. Change codes of 4,5, 7 or 8 are only allocated when entire CDs have either been split or amalgamated. Change codes of 0 and 9 are allocated when no redesign work has been carried out at all.