Advantage and disadvantage was operationalised as SEIFA quintile using the Index of Relative Socio-Economic Advantage and Disadvantage. See the "Create-df" script in this repository for the specifics of how this data was obtained from the ABS website and linked to cases in the CDSIRC database. For more about SEIFA in general read here: http://www.abs.gov.au/websitedbs/censushome.nsf/home/seifa.
Death category is defined by the Child Death and Serious Injury Review Committee and may be different to the cause of death determined by a doctor completing a death certificate, the Coroner and the ICD coder hired by the Committee. For definitions the Committee uses for its own work read the Annual Report here: http://www.cdsirc.sa.gov.au/wp-content/uploads/2017/11/2016-17-CDSIRC-Annual-Report.pdf.