3: Dementia prevalence and incidence

Monitoring the number of people living with dementia (prevalence) and the number of new cases of dementia each year (incidence) is required for policy development and service planning for health and aged care systems. Monitoring incidence over time indicates if the rate of diagnoses is increasing, decreasing or stable and whether certain population groups are more affected than others. However, this is difficult given the challenges of obtaining a timely diagnosis and lack of national general practitioner (GP) and specialist data with diagnostic information. See Timeliness of dementia diagnosis and Dementia diagnosis and management for more information.

Addressing the data gap and improving data

There is no single authoritative data source for deriving dementia prevalence in Australia, leading to varying estimates of how many people in Australia have dementia. Estimating dementia incidence is difficult because dementia is a gradual evolution of signs and symptoms rather than an acute event, and incidence requires information such as date of diagnosis and whether a diagnosis was made close to symptom onset (AIHW 2023a). There is no comprehensive source of information on dementia diagnosis date, meaning that dementia incidence is currently unmeasurable. National data on dementia incidence would also facilitate the estimation of dementia survival rates in Australia, which are currently not well understood. Accurate information on the number of Australians living with, and dying from, dementia in Australia is critical for monitoring trends and informing dementia policy and service planning (AIHW 2023a). Better data are also needed for the prevalence of different dementia types (for example, Alzheimer’s disease, vascular dementia) and severities, as well as people with mild cognitive impairment.

The Australian Dementia Network (ADNeT) Clinical Quality Registry, with its goal to register all Australians newly diagnosed with either dementia or mild cognitive impairment (ADNeT 2023), may be a future source of data that can contribute to estimates of dementia incidence at the population level. The ADNet Clinical Quality Registry is described in further detail at Dementia diagnosis and management.

Existing epidemiological studies on healthy ageing, especially when linked with existing administrative data that enable identification of people living with dementia, could also inform better estimates of dementia prevalence and incidence. For example, the Sax Institute’s Analysis of Population Traits and Risk Factors (ADAPTOR) study already links longitudinal data from over 200,000 participants from the 45 and Up Study with data on their use of hospitals, GPs, health services and prescription medication. Adding cognitive measures to existing studies could improve measures of dementia prevalence and incidence in Australia. There are challenges with this approach, as many existing surveys use volunteers which are not representative of the general population, where dementia risks and prevalence may be greater in those not participating in voluntary surveys (Brayne and Moffitt 2022).

Bringing together disparate data sources through data linkage would also help overcome some of the limitations associated with estimating the prevalence of dementia in Australia. Linked administrative data sets are currently being used to monitor dementia, and methodologies could be developed and refined using linked data to model estimates of dementia prevalence in Australia. However, data linkage is dependent on the capture of dementia and the quality of information provided in the individual data sets. At present, improvements are needed in available data sets and more types of data linked together. For dementia, available national data often capture people who have used a health, aged care or other type of support service, or people who died with a record of dementia, which skews towards capturing people who access services and/or who have more advanced dementia. Therefore, improvements in existing population-based studies and national surveys, or the development of new studies are needed to inform the estimation of dementia prevalence and mild cognitive impairment in Australia.

Proposed data improvement activities

There are 7 activities proposed to improve available data on dementia prevalence and incidence in the population. Some activities are directly focused on improving dementia prevalence and incidence data overall, while others are focused on improving or developing new data. Further, some activities are dependent on the completion of other activities in this plan.

Activities to improve dementia prevalence and incidence data include:

  • incorporate dementia data in enduring linked data assets to meet the needs of dementia monitoring
  • increase coverage of existing data for national dementia incidence monitoring
  • investigate approaches to estimate the national prevalence of dementia
  • assess new self-reported dementia data collected in the 2021 Census
  • estimate dementia prevalence in priority population groups
  • develop a Regional Insights portal of dementia data for local areas
  • assess impact of dementia coding changes in ICD-11 when incorporated in the Australian health system.

These activities may involve single projects, or multiple projects to enable monitoring of trends over time, incorporate improvements in data or to focus on a specific population group. Each activity provides information on the intended outcome, priority rating, level of investment required, timeframe for completion of the activity and who is responsible for undertaking the activity.

Activities aimed at improving dementia diagnosis data in primary and secondary health care data would also improve dementia prevalence and incidence data. See Dementia diagnosis and management for additional activities.