Dementia trends in England and WalesBMJ 2017; 358 doi: https://doi.org/10.1136/bmj.j3132 (Published 05 July 2017) Cite this as: BMJ 2017;358:j3132
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It is good to see a modelling exercise that links improvements in vascular health with the decline in dementia incidence. Until very recently public sector bodies have been working with projections for dementia that simply scaled up the CFAS I prevalence figures, an assumption that was inconsistent with improved vascular health, and which had no evidence base at all. At its limit this resulted in GPs being incentivised to find the ‘missing patients’ – and even then they couldn’t be found, as CFAS II finally clarified .
In the light of this it is not clear that the aggregate projection of a 57% increase in prevalence to 2040 is soundly based. The total projected increase amounts to 438,000 cases, of which about 357,000 is attributable to the 90 and over age group (figure 3). This represents a tripling of the numbers of people with dementia in this age group alone, although most demographic projections show that the 90+ population will only double in size. Why the modelling should be showing this implausible rise in age specific prevalence is unclear, but there are likely to be many assumptions underpinning the transition probabilities that could be reviewed to improve model calibration (for example CFAS II shows the greatest reductions in incidence in the 90+ age group ).
In similar vein the aggregate prevalence estimates show a steady upward trend from the base year of 2010, currently estimated at about 3% per year (figure 2). This might be expected if there was an historic upward trend, but my understanding of the CFAS II findings is that overall (unadjusted) numbers in 2007 were not dissimilar to those in 1993 (the estimated age standardised prevalence fell by 24%) . I am not aware of any recasting of past estimates to indicate what the underlying trend prior to 2010 is likely to have been, but 3% pa growth seems unlikely.
In the Balance of Care Group we have undertaken many policy and local service development studies over the last 20 years examining the potential for development of services for people with dementia. Our impression is that the very high projections that planners have had to work with until now have limited ambitions to develop linked community services, and we seem to have ended up with increasing reliance on care homes to do the heavy lifting.
So, while I agree with Albanese in the accompanying editorial  that it’s the prevalence figures that matter to policy makers and planners, there may be an opportunity here to inject a degree of optimism into the debate - which is rarely if ever heard - and which further fine tuning of this interesting model might well reveal.
The Balance of Care Group
 Matthews, F. E. et al. A two-decade comparison of prevalence of dementia in individuals aged 65 years and older from three geographical areas of England: results of the Cognitive Function and Ageing Study I and II. Lancet 382, 1405 (2013).
 Matthews, F. E. et al. A two decade dementia incidence comparison from the Cognitive Function and Ageing Studies I and II. Nat. Commun. 7:11398 doi: 10.1038/ncomms11398 (2016)
 BMJ 2017;358:j3132
Competing interests: No competing interests