Pitfalls in estimating secular changes in incidence and prevalence of dementia from administrative datasets

Abstract INTRODUCTION Administrative datasets can be used to calculate population incidence and prevalence of dementia. It is unclear how changes in data sources may affect these estimates. METHODS We obtained linked administrative health data for individuals 60 years of age or older in Western Australia for 1989–2019 ( n = 893,243) including hospital admissions, emergency department, cause‐of‐death, aged care assessment (from April 2003), and mental health services. RESULTS There was a marked increase in prevalence and incidence estimates over time. There appeared to be two phases: an initial increase attenuated by 1995–1999 and a rapid increase since 2000–2004 corresponding to inclusion of aged care assessments. There was a decrease in 2015–2019 coinciding with the unavailability of aged care assessment data. DISCUSSION An apparent secular change in rates of dementia over 31 years may be a product of increased propensity to record dementia diagnosis and availability of additional aged care data. Consistent comprehensive data coverage is required.