Study variables

Sociodemographic and presentation-related variables together with clinical variables were collected from the ED electronic database (SYMPHONY Version 2.29). The collected information included age, sex, country of origin, residential postcode, main language spoken at home, arrival mode, arrival time, presenting symptoms, a registered nurse-allocated triage urgency score that categorised the presentation as being an emergency (triage scores of 1 or 2), urgent (triage score of 3) or semi and non-urgent (triage scores of 4 or 5) and length of stay in the ED. The final main acute diagnosis reached on discharge from the ED was also collected together with the discharge destination. Among admitted patients, three possible admission departments were recorded: CCU, ICU and medical ward. The medical ward was used to categorise all adult hospital departments that did not have intensive specialised care. The admitting ward of patients transferred to another public or private hospital was also recorded and accounted for in this analysis. All diagnoses were identified using ICD-10-AM codes.

Each individual’s residential postcode was merged with the Australian Bureau of Statistics to obtain the Socio Economic Index For Areas (SEIFA) [19], estimated from the 2011 census data. SEIFA is a composite index of relative advantage or disadvantage based on geographic areas across Australia, with higher scores indicating less socioeconomic disadvantage. The SEIFA was further used to calculate a Relative Index of Inequality (RII) which is a regression-derived index summarising the magnitude of socioeconomic disadvantage while taking into account the sample size and the relative disadvantage experienced by each individual [20]. The estimated RII was further introduced as quintiles categorised according to the score’s distribution in the sample.