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Recent data from several countries, including Australia, indicate a notable trend of declining mental health, even before the COVID-19 pandemic. In Australia, this trend is particularly evident in the increasing rates of mental and behavioural issues as reported in the National Health Survey. From 2001 to 2020, these rates more than doubled, with a rise from 9.6 per cent to 21.4 per cent in individuals aged 15 and older. Similar patterns have been observed in many OECD countries, with a significant impact on younger populations.

This study delves into the reasons behind the increasing mental health challenges in Australia, focusing on three different phenomena – period, age, and cohort effects.

  • Period effects are changes experienced by all population groups simultaneously, such as economic crisis or environmental changes.
  • Age effects relate to shifts in the population’s age structure and have been studied through surveys showing a U-shaped pattern in mental well-being across ages (i.e. people are typically mentally well when young, often have a dip in mental wellbeing through their middle years, and then recover in older age).
  • Cohort effects, on the other hand, are unique to specific birth years and are influenced by societal shifts like the rise of social media or smartphone use.

The research employs various modelling techniques to differentiate these effects and assess how each contributes to an overall trend of declining mental health.

The research found that cohorts born recently, especially in the 1990s and later, report worse mental health than earlier cohorts at comparable ages. This trend is increasingly evident in more recent surveys, suggesting a strong cohort effect. The analysis, based on data spanning 20 years from the Household Income and Labour Dynamics in Australia (HILDA) survey, shows that younger cohorts are witnessing a quicker decline in mental health compared to older cohorts. These observations are consistent across various sensitivity analyses, including different ways of defining a cohort and measuring mental illness.

The consistency of these findings across genders,  accounting for various methods of measurement, show interventions are much-needed to address the challenges faced by these younger people. The authors believe that recognising and tackling the factors contributing to this decline, such as technological influences, economic stressors, and broader societal changes, is essential – especially as this burden of mental illness may not resolve itself over time (or certainly not fully), meaning it will have significant health system and economic impacts for decades to come.


Further information

Generational differences in mental health trends in the twenty-first century: Proceedings of the National Academy of Sciences (PNAS),

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