# 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.

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.

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.

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.