Aggregating data to larger areas

This page includes information on how to calculate percentages, IRSD scores, age-standardised rates and total fertility rates for aggregated areas.

You can set up these calculations in a spreadsheet, yourself, or use the template (xls) provided.

Percentages

Data that are expressed as a numerator, denominator and percentage are simple to calculate - refer to the example in the table below.

Example of how to calculate numerator, denominator and percentages for aggregated areas
Area Numerator Denominator Per cent
Constituent Area 1 51,485 858,490 6.0
Constituent Area 2 37,567 590,316 6.4
Constituent Area 3 63,124 887,873 7.1
Constituent Area 4 66,164 862,821 7.7
Aggregated Area 218,340
= Sum of constituent areas above		 3,199,500
= Sum of constituent areas above		 6.8
= Aggregated Area Numerator/ Aggregated Area Denominator x 100

 

Index of Relative Socio-economic Disadvantage

Index of Relative Socio-economic Disadvantage (IRSD) scores for aggregated areas are slightly more complicated. For these you need the IRSD score and the Estimated Resident Population (ERP) or Usual Resident Population (URP) of the constituent areas. Note: If a constituent area does not have an IRSD score it should be excluded from all calculations.

To calculate the IRSD score for an aggregated area you need to multiply the ERP or URP by the IRSD score for each of the constituent areas and then sum these together. This summation is then divided by the ERP or URP of the aggregated area to give you the aggregated area's IRSD score - refer to the example in the table below.

Example of how to calculate IRSD scores for aggregated areas
Area IRSD score ERP or URP IRSD x ERP or URP
Constituent Area 1 1043 798,712 833,056,616
Constituent Area 2 1006 548,568 551,859,408
Constituent Area 3 939 840,623 789,344,997
Constituent Area 4 994 810,788 805,923,272
Aggregated Area 994 = Sum of (IRSD x ERP or URP)/ Sum of ERP or URP
(i.e., 2,980,184,293/ 2,998,691)
 2,998,691
= Sum of constituent areas above		 2,980,184,293
= Sum of constituent areas above

 

Age-standardised rates

Age-standardised rates are a little more complicated to calculate. Without access to the raw data used to calculate the rates of the data you have, you will need to approximate the age-standardised rates for aggregated areas - refer to the example in the table below. Although not perfect, the rates calculated this way are very close to the actual rates that would be calculated from the raw data.

Example of how to calculate age-standardised rates for aggregated areas
Area Number Rate Number/ Rate
Constituent Area 1 5,262 16.7 315.1
Constituent Area 2 2,717 16.8 161.7
Constituent Area 3 5,900 14.5 406.9
Constituent Area 4 13,320 12.9 1,032.6
Aggregated Area 27,199
= Sum of constituent areas above		 14.2
= Sum of constituent areas/ Sum of Number/Rate (i.e., 27,199/1,917)		 1,917
= Sum of Number/Rate

Note: You can use either an actual rate or standardised ratio in the calculations above, depending on which you want to report on.

Total fertility rates

Total fertility rates can be produced using the same method as for age-standardised rates, where ‘Number’ is the number of births and the 'Rate' is the total fertility rate.