In 2005 it was estimated that the number of people with dementia in Australia reached 200,000 [1
]. Recent projections indicate that if there is no risk reduction at the population level, the number of people with dementia in Australia will exceed 730,000 by 2050 [2
]. In Australia, dementia will cause the largest burden of disease for women and 5th largest for men by 2016 [3
]. These Australian figures were derived using a similar methodology to European studies that project future population characteristics by age and sex [4
] and took into account prevalence estimates from four meta-analyses of mostly European studies [5
]. Consequently, estimates of dementia prevalence in Australia are typically based on non-Australian studies and it is necessary to compare those estimates derived from European and North America studies with large scale Australian studies.
Many of the dementia prevalence studies included in the source meta-analyses [5
] were published 15 to 50 years ago, with the actual data often having been collected years prior to publication. For example, one meta-analysis is based on articles published between 1945 and 1985 [8
], another analysed articles published between 1981 and 1991 (mean publication year 1988) [6
] and a third covered publications between 1987 and 1994. Not all studies contributing to these meta-analyses were population-based studies as some of the samples were drawn from medical practitioner lists [6
]. Diagnostic criteria for dementia have changed since these studies were conducted and the methodology of meta-analyses has also become more rigorous with the publication of guidelines [9
] and the development of the Cochrane Collaboration.
Whilst acknowledging that meta-analyses are the preferred method for aggregating data on dementia prevalence [1
], their limitations prompt closer scrutiny of complementary sources of data. This is particularly important because prevalence estimates are used for service planning, and estimates of health care costs and burden of disease. When projected up to the population, small differences in prevalence rates have large implications for estimating health care costs. For example, 1% increase in dementia for the year 2003 in Australia would have cost approximately AUD $217 million [11
The aim of the present study was to compare prevalence of probable dementia and cognitive impairment using MMSE cut-offs [12
] with dementia prevalence estimates[1
] generated by application of techniques used in meta-analyses of European studies. The MMSE, was chosen because it is the most widely used screening instrument for dementia. Furthermore, the MMSE is used almost universally in clinics [13
], is recommended as a dementia screen by the U.S. Preventive Services Task Force [14
], has been translated into many languages, and has psychometric properties that have been well documented in many contexts [15
The current methodology was adopted not only because existing projections have relied on estimates that are at least 15 years old and largely based on meta-analyses of European data, but also because there is no national study of dementia prevalence in Australia that uses clinical diagnoses. This is in part due to the cost of acquiring dementia diagnoses and the logistical difficulty of conducting a national prevalence study over such a large land mass, in comparison to geographically smaller countries. Data come from two sources: Australian Bureau of Statistics (ABS) Surveys and a pooled, harmonized, dataset from DYNOPTA [16
]. The latter includes three independent regional studies that have reported dementia prevalence in Australia, but none of these studies individually is large enough on which to base national estimates. These include the Sydney Older Persons' study (SOPS) that used a clinical diagnosis [17
], the Canberra Longitudinal Study (CLS) that used an algorithm based on data collected by a trained interviewer [19
], and the PATH Through Life Study (PATH) [20
] that includes a clinical assessment but which to date has identified very few cases because the sample is too young. These three studies all included the Mini-Mental State Examination as did a fourth study contributing to DYNOPTA, the Australian Longitudinal Study of Ageing (ALSA). While the latter did not include a clinical assessment of dementia, it included a cognitive assessment, and cognitive decline and impairment has been a focus of the investigators. The ABS surveys recently have incorporated the MMSE, providing an additional source of data to evaluate for the estimation of probable dementia prevalence.