Index of Household Advantage and Disadvantage (IHAD): Technical Paper

The Index of Household Advantage and Disadvantage (IHAD) is an analytical product developed by the Australian Bureau of Statistics (ABS) that summaries relative socio-economic advantage and disadvantage for households. 

A household is defined as one or more persons, at least one of whom is at least 15 years of age, usually resident in the same private dwelling. All occupants of a dwelling form a household. For Census purposes, the total number of households is equal to the total number of occupied private dwellings (Census of Population and Housing: Census Dictionary, 2021). This report will refer to ‘household’ rather than dwelling, as the index is designed to represent advantage and disadvantage at household level. 

IHAD uses information from the 2021 Census of Population and Housing (2021 Census) on the characteristics of each household and the people living within them.

In comparison, ABS's Socio-Economic Indexes for Areas (SEIFA) provides index values calculated for each geographic area, and not for each household. Within any area there are likely to be households with different characteristics to that generally measured across the overall population of that area. For example, a relatively advantaged area is likely to contain households that are relatively advantaged; however, the same area is also likely to contain some households that are relatively disadvantaged.

The IHAD data complement the area level rankings given by the SEIFA Index of Relative Advantage and Disadvantage (IRSAD), by allowing the relationship between area level disadvantage/advantage and household level disadvantage/advantage to be explored. IHAD quantiles summarise the diversity of area level advantage and disadvantage at household level, adding value to the use of SEIFA IRSAD for research and planning at the area level.

Because IHAD is derived at household level it can be cross classified with other Census variables not included in the index. This could be used to assist in exploring advantage and disadvantage for different population groups. 

Some common uses of IHAD include:

• assisting research into the relationship between socio-economic disadvantage and various social outcomes, for different demographic groups, and
• assisting decision making in funding and services to areas, alongside other relevant data sources. 

This paper provides information on the concepts, data, and methods used to create IHAD 2021. The paper also contains discussion of the recommended methods for interpretation and use of the index.

This paper is intended to be a comprehensive reference for IHAD 2021. Refer to the Methodology paper for basic information that has been prepared for a general audience.

This paper uses terminology relating to the 2021 Census data. The Census of Population and Housing: Census dictionary, 2021 provides a glossary and explanations of the 2021 Census variables. 

The Index of Household Advantage and Disadvantage (IHAD) was first produced as an experimental index in 2018, based on 2016 Census data and funded by the ACT government. IHAD 2021 is the second release of this household level index and is funded by the Australian Government Department of Education. Future releases of an IHAD product by the ABS are contingent on interest and funding from stakeholders. IHAD is not part of the ABS ongoing work program.

This section highlights some important features of IHAD 2021, and how they compare with the Experimental IHAD 2016.

The ABS has aimed to maintain consistency between IHAD 2021 and the previous release. However, some changes have been made and are described below.

IHAD 2021 uses the Australian Statistical Geography Standard (ASGS) Edition 3 (2021). The structure of the ASGS Edition 3 is similar to the structure of ASGS Edition 2 (2016), though there have been updates to SA1, SA2, and other ASGS boundaries in some areas. For more information about the ASGS, refer to Changes from the previous edition of the ASGS.

Occupation variables for the Experimental IHAD 2016 were based on the Australian and New Zealand Classification of Occupations, 2013 (ANZSCO), version 1.2A. For 2021, the updated version, ANZSCO version 1.3, was used, resulting in some changes to skill level and some title changes. Variables using cut-off values in their definitions, such as high and low income, were updated to use new cut-off values. For more information about how the cut-off values were selected, refer to the Description of candidate IHAD variables. 

The ‘Does any member of this household access the internet from this dwelling?’ question was not asked in the 2021 Census, so the NONET variable (derived from the output NEDD - Dwelling Internet Connection variable) could not be used when calculating the IHAD 2021 scores.

IHAD output includes a general introduction to IHAD 2021, a basic Methodology, this Technical Paper, and data which can be sourced from:

• Data cubes for a range of geographies (SA1, SA2, States and Territories)
• TableBuilder data
• Interactive maps
• Web services

Output includes 

• proportions of households in each IHAD quartile, 
• usual resident population,
• SEIFA IRSAD quartile (where applicable), 
• occupied private dwelling count (where applicable), and 
• dwelling count (where applicable),

Where applicable, outputs are consistent with the release of these items in the SEIFA product (Socio-Economic Indexes for Areas (SEIFA), Australia, 2021) and in Census of Population and Housing: Mesh Block Counts, 2021. For SA1 and SA2 outputs, areas without a SEIFA score will also not be assigned IHAD quantile proportions.

Sums of IHAD quartile 1 through 4 proportions for each area (i.e. row) may equal more than 100% due to rounding and random adjustments made to the data. When calculating proportions, percentages, or ratios from tables of cross-classified or small geographic areas, the random error introduced can be ignored except when cells containing very small numbers of households are involved, in which case the impact on percentages and ratios can be significant. For more information see Introduced random error / perturbation.

Data cubes are available from the Data downloads section:

• Statistical Areas Level 1: Household level; the percentage of households within each IHAD quartiles;
• Statistical Areas Level 2: Household level; the percentage of households within each IHAD quartiles;
• State and territory: Person level; the percentage of persons within each IHAD quartile

Census TableBuilder Pro is an online data tool that enables you to cross classify indexes and household indicators with all the levels of geography available.

To set some context for the rest of this paper, it is worth briefly touching on some important characteristics of the index.

The IHAD measures are assigned to households, not to individuals. They indicate the collective socio-economic characteristics of the people living in a household.

As a measure of socio-economic conditions, the index can be used to understand the distribution of these conditions across different households. Index scores are on an arbitrary scale. The scores do not represent some quantity of advantage or disadvantage. For example, we cannot infer that a household with an index score of 1000 is twice as advantaged as a household with an index score of 500.

IHAD is constructed based on a weighted combination of selected variables. The indexes are dependent on the set of variables chosen for the analysis. A different set of underlying variables would result in a different index.

The index is primarily designed to compare the relative socio-economic characteristics of households at a given point in time. It can be very difficult to perform useful longitudinal or time series analysis, and this sort of analysis should be undertaken with considerable care.

There is more discussion of these points in Using and Interpreting IHAD.