Curiouser and curiouser: the changing numbers in dementia diagnosis

ZPrS_Z4mTom Dening is Professor of Dementia Research at the Institute of Mental Health at the University of Nottingham. He tweets at @TomDening

Dementia is getting more common as the population of the UK and, for that matter, the world gets older. But just how common? How many people are out there? It’s a really important question for us all.

There have been some interesting developments over the last year. Until then, the official figure was 800,000 in the UK. This was based on projections from the MRC Cognitive Functioning and Ageing Study (CFAS), data that were collected during the 1990s, and updated based on the demographic profile of the elderly population since then. So this figure was based on numbers around 20 years old.

Therefore it was important to replicate the study and eventually CFAS II was funded and carried out. The team reported their findings in the Lancet last year. The most important result was that instead of an expected prevalence for dementia of 8.3% in people aged over 65 (giving over 800,000 cases) they found a prevalence rate of 6.5%, which would result in a lower total number of around 670,000. In other words, the total might be as much as 20% less than generally assumed. The most likely reason for this would be a cohort effect – i.e. people born later in the 20th century had enjoyed better health, nutrition, education etc and therefore were living into old age in better general health and with less burden from vascular disease.

The response to this was mixed. To me, it seems like jolly good news if public health has improved and there is less dementia than we expected. Other authorities expressed concern that the CFAS II figures might be overoptimistic, and concerns about having more than one figure being used. It was agreed to establish a Delphi process to review the evidence. The Delphi method is a systematic, interactive forecasting method by which a panel of experts, led by a facilitator, use a series of iterated questions to arrive at a consensus. The advantages of this method are obvious – you can use all the known literature and experts can respond to new findings, hopefully reaching the Truth in the end. From the outside, it may look like a clique.

The results of the process have been published by the Alzheimer’s Society in their Dementia 2014 report, though so far only an overview is available.  The crucial figure is now 835,000, or 850,000 in 2015. Slightly surprisingly, this total number has gone up rather than down, despite the CFAS II findings. It represents a prevalence of 7.1% in people aged 65 and over.

At the same time, the Department of Health and NHS England, concerned at apparently low (and variable) rates for diagnosing dementia, have been trying to improve the situation. Most of the effort has been concentrated on GPs, with the aim to have at least two-thirds of people with dementia having a diagnosis. Clearly, the size of the task depends on the denominator: the CFAS II figure suggests that the required number would be about 440,000 and the Dementia 2014 figure would be nearly 600,000.

The third development is that it is widely reported that NHS England has now introduced an incentive payment for GPs based on patients diagnosed with dementia. Payments to GPs are increasingly based around incentives of various kinds but this particular initiative has drawn a lot of criticism (see, for instance, comments on as it has been suggested that this creates financial pressure to push patients into a particular diagnostic category, which can of course have serious implications. Clearly, there is public unease about this, even if some of it is based on a misunderstanding of the complex world of GP payments.  Will £55 push unscrupulous GPs to make fraudulent diagnoses of dementia? Possibly not, but it may subtly alter the threshold at which people are diagnosed as having the condition.

It is a complex and changing situation, but it would be unfortunate if we do too much that causes older people or their families to feel suspicious about the activities or motivations of their doctors. When I explain the NHS to visiting scholars from the planet Zar, they are very interested in the Dementia Challenge. A thoughtful student asked me, “So why is it that the Earthlings are counting more of these cases than actually exist and why are they asking doctors to diagnose a made-up number of cases, and is it good for anyone that they get paid for this?” Good question.

One thought on “Curiouser and curiouser: the changing numbers in dementia diagnosis

  1. Thank you for a very helpful & clear summary of the (complex and evolving!) situation.
    My one query is: who is making the diagnosis of dementia?
    Where I practice, our local (generally extremely good) GPs very rarely make this diagnosis themselves. In fact, if anything they have historically often avoided doing so, even in fairly advanced cases, because of the lack of infrastructure to support people after the diagnosis has been made. Patients with suspected dementia are generally referred to the memory clinic for formal assessment and diagnosis.
    Thus, although GPs may well receive payments for diagnosis, the diagnosis itself (rather like cancer 2 week wait cases generally made and/or ratified by MDTs) is made in secondary care by an expert team. I therefore see no conflict of interest here.
    Maybe things are done differently elsewhere? It seems to me that this diagnosis is one that is particularly important to be made properly, for those who wish a diagnosis. It is equally the case that it is a diagnosis which can be difficult to be sure of. For both these reasons, would it not be sensible to leave the diagnostic process in the hands of those with the expertise and resources to undertake the process, currently mainly in secondary care – assuming the necessary resources are available?

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