The Personality & Total Health (PATH) Through Life project is a large, on-going, population-based, longitudinal cohort study comprising approximately 7500 participants ranging from early to late adulthood. The project aims to track and define the lifespan course of depression, anxiety, substance use and cognitive ability, identify environmental risk and protective factors within these domains, and examine the relationships between depression, anxiety and substance use with cognitive ability and dementia.

The PATH Through Life project is a 20 year longitudinal cohort study of 7,485 young (aged 20–24 at baseline), midlife (aged 40–44 at baseline) and older (aged 60–64 at baseline) adults randomly sampled from the electoral roll of the Australian Capital Territory and the nearby city of Queanbeyan.

The original aims of the project are outlined below.

• To delineate the course of depression, anxiety, substance use and cognitive ability with increasing age across the adult life span.
• To identify environmental risk, genetic risk and protective factors influencing individual differences in the course of these characteristics.
• To investigate interrelationships over time between the three domains of: depression and anxiety, substance use, and cognitive ability and dementia.

These broad aims relate to clinical outcomes that constitute the major burden of disease within the Australian community, and continue to provide the core direction for the project. Additional aims incorporated into the third wave of data collection (currently underway) focus on the mental health related impact of various personal, social and lifestyle transitions and events experienced by the different age cohorts. These include:

• infertility, fertility and pregnancy
• changes in family structure, relationship formation and separation
• menopause
• retirement.

Several design features of the PATH project contribute to its unique standing among population based longitudinal cohort studies.

• Obtaining measures of genetic, biological (including MRI), psychosocial and lifestyle risk and protective factors for mental health and wellbeing.
• Use of a narrow age cohort design with longitudinal follow ups as an optimal means of separating age and cohort effects.
• Assessment of participants across the full adult lifespan, permitting investigation of developmentally significant, but under studied periods such as midlife
• Recruitment and follow up of a young-old population, providing important pre-clinical data for studying the development of age related changes in memory and cognition.