Methods

A Systematic review of papers reporting on the prevalence of dementia was performed. Using a Medline and Embase search we found a number of studies using the search terms “Dementia / Prevalence / Incidence / Epidemiology” or “Alzheimer’s Disease / Vascular dementia, Lewy-body disease/ Fronto-temporal dementia/ Incidence / Prevalence / Epidemiology. This was followed by hand searching these papers. A database of studies was compiled and those fulfilling predetermined quality criteria were invited to submit data for the collaborative analysis

Collaborative analysis

Inclusion criteria (Table 1) for involvement in the collaborative analysis were decided by the members of the EUROCODE prevalence working group. These were developed by consensual opinion looking at all methodological domains of this type of epidemiological study. Criteria were aimed to identify those studies of highest quality. Studies fulfilling criteria were invited to participate in the collaborative analysis. Age (by 5 year age group from 50 to >95years) and sex specific raw prevalence case numbers and underlying population were collected from all groups agreeing to participate in the collaborative analysis.

Table 1

Analysis

Age (5 year age range) and sex specific raw data from participating studies was included in the analysis. Data above 95 years was combined. Below this age raw data that could not be presented in 5 year age groups was excluded from the analysis. Age and sex specific prevalence’s were calculated using the total number of prevalence cases from all studies as the numerator and total population examined as the denominator. In this way weighting was achieved by each study’s sample size.

Results

A total of 194 articles were identified from the literature search. 31 studies were identified as possible for inclusion in collaborative analysis and they were invited to submit data. Raw data was obtained from 17 studies and used in the collaborative analysis of dementia prevalence rates in Europe. Table 2 outlines the 31 studies identified for participation and if not finally included the reason for non inclusion in yellow.

Table 2

Prevalence rates from individual studies.

Table 3 shows the basic characteristics of each study included in the collaborative analysis with differences in geographical region, study size and age range of population evaluated.

 Table 3

Prevalence rates from collaborative analysis.

Table 4 shows male age and sex specific prevalence rates of dementia

Table 4

 Table 5 shows female age and sex specific prevalence of dementia

Table 5

Total age specific prevalence rates were calculated by pooling data on prevalence case numbers and underlying population for males and females in each 5 year age range. Table 6 shows these rates

Table 6

Comparison with previous data.

Figures 1 and 2 show graphically the comparison of the current data with that from the EURODEM project.

Figure 1

Figure 2

Discussion

From the current collaborative analysis it appears that for the majority of age groups dementia prevalence has not changed significantly over the last few decades despite the current analyses using completely new data from that included in EURODEM. Within the oldest old however dementia prevalence is higher in females and this level of prevalence has not been previously documented. This finding may be as a result of a higher proportion of studies reporting dementia prevalence in the older age ranges over the last 2 decades and probably reflects a true rate in this previously under reported population.

A comparative table of the estimated number of people with dementia (based on 2006 population statistics) was created by Alzheimer Europe after the end of the EuroCoDe study and can be found at:

http://ec.europa.eu/health/ph_information/dissemination/echi/docs/dementia2_en.pdf

At the end of 2013, these calculations will be updated using 2013 population statistics.