Table 1 Defining the social determinants and scenarios of improvement

Social cohesion

Based on the Scanlon–Monash Index of Social Cohesion, this represents the willingness of members of society to cooperate with each other in order to survive and prosper. There are five domains this index seeks to capture: belonging; worth; social justice and equity; political participation; and acceptance and rejection⁷⁵. The five domains are transformed to a single composite index using factor analysis and assigning weights to each indicator, with 2007 as the reference year assigned the starting index of 100. Further detail on the methods used by the Scanlon–Monash research group can be found in a report by Markus et al.⁷⁶, and https://www.monash.edu/mapping-population. The average annual decline between 2011 and 2023 in the Scanlon–Monash Index was by 0.788 units, and this was assumed to continue each year of the model timeframe in a linear fashion as part of the business-as-usual scenario.

Scanlon–Monash Index of Social Cohesion⁷⁵

The social cohesion index continues to decline in future years but at a reduced rate by applying a multiplier of 0.95 to the baseline average annual rate of change from January 2024 onward. Each year, the index will decrease by 0.7486 (0.788 × 0.95).

Early life and childhood behavioral and emotional difficulties (shortened to ‘childhood difficulties’ in text, tables and figures)

Childhood difficulties (early life and childhood behavioral and emotional difficulties) refers to the outcome of a brief screening questionnaire (SDQ) that measures behavioral and emotional difficulties in children and young people⁶⁷. In our model, the population aged less than 12 years is partitioned to one of three levels of distress: ‘close to average’, ‘slightly raised’ or ‘high’ SDQ levels. Higher levels of SDQ can be an indicator of early life difficulties, adverse experiences or trauma. Rates by which people flow between the three levels of SDQ are dependent on age, rates of engagement with the mental health services system, rates of treatment and the population levels of social cohesion.

The Longitudinal Study of Australian Children, Growing up in Australia^77,78

The rate at which children transition to higher levels of SDQ was reduced by applying a multiplier of 0.95 from January 2024 onward.

Homelessness

Following the Australian Bureau of Statistics (ABS), homelessness refers to a state in which an individual does not have a permanent living arrangement, no fixed place of residence, and no suitable or adequate accommodation alternatives⁷⁹. People aged 15 and older enter homelessness at rates that are dependent on age, levels of psychological distress, unemployment and substance misuse. For people under the age of 15 years, rates of entering homelessness are dependent on age.

ABS⁸⁰

The rate at which people enter homelessness was reduced by applying a multiplier of 0.95 from January 2024 onward.

Unemployment

Following the ABS, unemployment is defined as a state in which an individual who is of working age and ability, and who is actively seeking and available for work, is not employed in any paid work or self-employed work. People can transition between the states of being sufficiently employed, underemployed, unemployed or not-in-the-labor-force.

ABS^81,82,83

The rates at which people enter unemployment from being sufficiently employed or underemployed was reduced by applying a multiplier of 0.95 from January 2024 onward.

Discontinue secondary education

Discontinuing secondary education refers to when a student enrolled in any high school grade between grade 7 and 12 withdraws their enrollment. Rates of discontinuation are dependent on levels of psychological distress in the population aged 12–17 years.

Australian Curriculum, Assessment and Reporting Authority (ACARA)⁸⁴

The rate at which students discontinue secondary education was reduced by applying a multiplier of 0.95 from January 2024 onward.

Discontinue tertiary education

Discontinuing tertiary education refers to when an individual attending education for a qualification at certificate III or above withdraws their enrollment. Rates of discontinuation are influenced by psychological distress.

ABS^83,85

The rate at which students discontinued tertiary education was reduced by applying a multiplier of 0.95 from January 2024 onward.

Substance misuse

We followed the ABS’ definition of 12-month substance use disorder, and here, we refer to this as substance misuse. Substance misuse refers to the use of alcohol and other drugs in a way that produces harm to the consumer of the substance and others. Harm associated with substance misuse can include a deterioration of an individual’s mental and physical health, financial state, social connectedness, education and employment. The rate at which people develop substance misuse is dependent on homelessness, levels of young people aged 15–24 not in education nor employment, levels of psychological distress and recovery from substance misuse treatment services.

ABS^86,87

The rates at which people developed 12-month substance use disorder was reduced by applying a multiplier of 0.95 from January 2024 onward.

Underemployment

Based on the ABS’ definition, underemployment refers to a state in which an individual is employed in paid work but has indicated that they would prefer to work more hours. People can transition between the states of being sufficiently employed, underemployed, unemployed or not-in-the-labour-force.

ABS^81,82,83

The rates at which people transition from being sufficiently employed into underemployment were reduced by applying a multiplier of 0.95 from January 2024 onward.