Estimating the prevalence of dementia using multiple linked administrative health records and capture-recapture methodology.

Background: Obtaining population-level estimates of the incidence and prevalence of dementia is challenging due to under-diagnosis and under-reporting. We investigated the feasibility of using multiple linked datasets and capture-recapture techniques to estimate rates of dementia among women in Australia.

Methods: This work is based on the Australian Longitudinal Study on Women's Health. A random sample of 12,432 women born in 1921-1926 was recruited in 1996. Over 16 years of follow-up records of dementia were obtained from five sources: three-yearly self-reported surveys; clinical assessments for aged care assistance; death certificates; pharmaceutical prescriptions filled; and, in three Australian States only, hospital in-patient records.

Results: A total of 2534 women had a record of dementia in at least one of the data sources. The aged care assessments included dementia records for 79.3% of these women, while pharmaceutical data included 34.6%, death certificates 31.0% and survey data 18.5%. In the States where hospital data were available this source included dementia records for 55.8% of the women. Using capture-recapture methods we estimated an additional 728 women with dementia had not been identified, increasing the 16 year prevalence for the cohort from 20.4 to 26.0% (95% confidence interval [CI] 25.2, 26.8%).

Conclusions: This study demonstrates that using routinely collected health data with record linkage and capture-recapture can produce plausible estimates for dementia prevalence and incidence at a population level.