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Why patients are not like badgers

Owen Paterson, the Environment Secretary, has got egg on his face. Having spent months arguing the case that our countryside was rife with consumptive badgers spreading disease left, right and centre, it turns out that there aren’t as many of the elusive creatures as he thought. The original estimate of 2,400 badgers in the area of the cull has proved to be rather embarrassing, since the company responsible for performing the cull has only managed to kill 850 - well short of the 70% target required to make the cull effective. Whether it’s the badgers that have moved the goalposts, as Mr Paterson claims, or his department has fudged the figures to make the target easier to hit, the new estimate for badgers in the wild has been revised downwards to 1,450.

Whatever the rights and wrongs of the badger cull, there is an important lesson to be learned - making estimates of what is out there is difficult, and if you set a target based on those estimates things can go horribly wrong. Prevalence estimates of disease have been with us for a long time. They help us to understand the epidemiology of particular diseases, and track changes over time; they are useful for estimating the provision of necessary resources when designing health policy - but what they have not been used for, until now, is to set diagnostic target rates.

I may be mistaken, but it seems to me that when the government set a target diagnosis rate of 65% for dementia, they were doing something quite new in health policy, and setting a dangerous precedent in doing so. Diagnosis rates are reported to be below 50%, but are based on questionable estimates that are 20 years out of date. The latest figures suggest that there are fewer cases of dementia than we thought - but the government shows no sign of revising its figures. The target, inevitably, is linked to proactive policies to find new cases - the hospital CQUIN and the GP DES being the prime examples. The question we need to ask, however, is this: what if the estimates are wrong?

When it comes to badgers, at least we can take comfort in the fact that other woodland creatures are unlikely to be mistaken for a badger and included in the cull to make up the numbers. Unfortunately, patients with dementia don’t walk round with distinctive black and white markings, and there is every possibility that all manner of other cases could be caught up in the net of dementia in the drive to increase diagnosis. From mild cognitive impairment to depression, delirium or just plain natural ageing, overdiagnosis is a very real danger.

If we accept this misuse of prevalence data in the dementia debate, and fail to expose the dangers of setting target diagnosis rates, then we can expect more target-driven initiatives to follow - and overdiagnosis, with all its attendant harms, will rise to new heights.

Dr Martin Brunet is a GP in Guildford and programme director of the Guildford GPVTS. You can tweet him @DocMartin68