Using and interpreting IHAD

The IHAD is constructed at the household level, based on the assumption that economic and other resources are generally shared within households, and therefore persons within households will share similar levels of socio-economic advantage and disadvantage. However, this may not always be the case, particularly for multi-family households, group households, and households containing lodgers or boarders. It is possible for a relatively advantaged person to be a resident in a relatively disadvantaged household or a relatively disadvantaged person to reside in a relatively advantaged household.

Quantiles are created based on assigning, as near as is practicable, equal numbers of households into each quantile (rather than equal numbers of persons). As larger households tend to have higher index values, more advantaged deciles tend to contain larger numbers of persons.

IHAD is constructed using a weighted combination of selected variables. The index is dependent on the set of variables chosen for the analysis. A different set of underlying variables would result in a different index. However, due to the large number of variables in IHAD, removing or altering a single variable will usually not have a large effect.

Users should consider the aspect of socio-economic advantage and disadvantage in which they are interested and examine the underlying set of variables for IHAD. This will allow them to make an informed decision on whether IHAD is appropriate for their particular purpose. 

As the IHAD is constructed using Census variables, when undertaking analyses involving cross-tabulation of the IHAD with other Census variables, users should examine the variables contained within the index to aid in the interpretation of those results. Refer to Technical details for IHAD: variables and loadings for details of variables that were included in the IHAD.

The index is designed to compare socio-economic characteristics of a household at a point in time, not to compare households over time. There are several issues that make longitudinal or time series analysis of IHAD difficult to interpret.

• The constituent indicators and indicator weights for the index are likely to have changed.
• The distribution of the standardised index values will have changed (e.g., a score of 800 does not represent the same level of disadvantage in different years).
• Census variable changes will affect the variables used to calculate the IHAD scores.

Topics represented in IHAD are limited by the variables collected in the Census.

Measures relating to wealth, access to services, and social/community participation may provide more information about the relative advantage or disadvantage within a household, but these measures are not collected in the Census.

Long-term health conditions, asked for the first time in the 2021 Census, were not included in IHAD. This is to allow health researchers to analyse the relationship between health outcomes and socio-economic advantage/disadvantage. Adding health variables to IHAD would make these relationships less clear.

Other potential topics that could be associated with advantage and disadvantage but are not captured in the Census include crime, and the environment. If data were available on these topics, they may provide additional information about the level of advantage and disadvantage present within households that could result in households being assigned a different index value.

Mapping IHAD provides an excellent way of observing the spatial distribution of relative socio-economic advantage and disadvantage. Interactive maps at SA2 level are available for 2021 IHAD.