Bisphenol A exposure is not associated with area level socioeconomic index in Australian children using pooled urine samples

Heffernan AL, Sly PD, Toms LML, Hobson P, Mueller JF

ONLINE RESOURCE 1:Background information on the construction of Socioeconomic Index for Areas in Australia (SEIFA), and its application in the pooling protocol used in this study

The Australian Census of Population and Housing is conducted every five years by the Australia Bureau of Statistics (ABS). The objective is to accurately measure the number of people and dwellings in Australia and a range of their key characteristics on census night (Pink, 2011). The socio-economic indexes for areas (SEIFA) is a product developed by the ABS that summarises a number of socioeconomic variables that represent disadvantage in the area based on information that is collected from the census (Adhikari 2006; Pink 2008a; 2008b). The data is publicly available and can be downloaded from the ABS website (ABS 2008).At the onset of the study, the most recent SEIFA and census data available was from 2006. For this study, only postal areas from Queensland (n=426) were used.There four current SEIFA indices are:

  1. The Index of Relative Socioeconomic Disadvantage (IRSD)
  2. The Index of Relative Socioeconomic Advantage and Disadvantage (IRSAD)
  3. The Index of Economic Resources
  4. The Index of Education and Occupation

The indices measure different aspects of socioeconomic conditions that have been derived using principal component analysis(ABS, 2011). IRSD and IRSAD are the most commonly used indices in health and social research. As IRSADsummarises area-level variables that represent relative advantage and relative disadvantage, it can be used to measure advantage and disadvantage in a continuum, rather than being limited to measures of relative disadvantage, as in the case of IRSD (Adhikari 2006). There are 21 variables incorporated into the IRSAD score, including:

  • % People aged ≥15 years with no post-school qualifications
  • % Occupied private dwellings with no internet connection
  • % People with stated annual household equivalisedincome between AUD$13,000 – $20,799
  • % Employed people classified as labourers
  • % Households paying rent less than AUD$120 per week (excluding AUD$0 per week)
  • % People <70 years who have a long-term health condition or disability and need assistance with core activities
  • % Employed people classified as machinery operators and drivers
  • % People in the labour force that are unemployed
  • % One parent families with dependent offspring only
  • % Households renting from Government or community organisation
  • % Employed people classified as low skill community and personal service workers
  • % Occupied private dwellings requiring one or more extra bedrooms (based on Canadian National Occupancy Standard)
  • % Occupied private dwellings with no car
  • % Occupied private dwellings with four or more bedrooms
  • % People aged ≥15 years at university or other tertiary institution
  • % Households paying mortgage greater than AUD$2,120 per month
  • % Households paying rent greater than AUD$290 per week
  • % People aged ≥15 years with an advanced diploma or diploma qualification
  • % Employed people classified as professionals
  • % Occupied private dwellings with a broadband internet connection
  • % People with stated annual household equivalisedincome >AUD$52,000

To generate the index geographical areas are given an IRSAD score, where a low score indicates relatively greater disadvantage and a general lack of advantage, and a high score indicates a relative lack of disadvantage and greater advantage in general (Pink 2008a, 2008b; ABS 2011). All areas are ordered from lowest to highest score, and the area with the lowest score is given a rank of 1, the area with the second lowest score is given a rank of 2, and so on.

To create the pooling strata, the population fraction for each postal area was calculated by dividing the known population for each postal area by the total population for the state. The population fractions for different postal areas were combined to give equal quintiles, where quintile 1 (Q1) contains 20% of the population with the highest scores, and Q5 contains 20% of the population with the lowest score.

The reader is directed to the following technical papers published by the Australian Bureau of Statistics for further information:

Adhikari P (2006) Socioeconomic Indexes for Areas: Introduction, Use and FutureDirections. Cat.No. 1351.0.55.015.Australian Bureau of Statistics.

Australian Bureau of Statistics, (2008)SEIFA, Postal Area, Data Cube only, 2006.

Australian Bureau of Statistics (ABS) (2011) Measures of socioeconomic status. Report number 1244.0.55.001. Australian Bureau of Statistics, Canberra.

Pink B (2008a) Information paper: An introduction to Socio-economic indexes for area (SEIFA). 2006 Cat. No. 2039.0. Australian Bureau of Statistics.

Pink B (2008b) Socio-economic indexes for area (SEIFA) - Technical paper. 2006 Cat. No. 2039.0.55.001. Australian Bureau of Statistics.