Practices are intended to earn more for quality points in clinical areas in which they have disease prevalence above the national average.
However, a flaw in the formula means that practices with abnormally high prevalence figures can deny income to even those practices with above-average prevalence (GP, 13 October).
This is because the prevalence formula is based on the range of prevalence, which can be hugely increased by a single practice.
In 2006/7, one practice in County Durham that only treats nursing home patients recorded 55.5 per cent of its 254-strong list as having dementia - 139 times the national average.
As a result 8,350 other practices received identical prevalence weighting for dementia. Quality points were valued the same for practices with anything from no prevalence to almost seven times the national average.
A London care home registered as a GP practice has the highest disease prevalence in England in seven clinical quality domains, with prevalence up to 12 times the national average in areas such as stroke, chronic kidney disease and AF.
GP has calculated that practices with an average list size and slightly above-average prevalence in most of the disease domains could be losing up to £5,500 in a year.
GPC chairman Dr Laurence Buckman said the GPC and NHS Employers were looking for solutions.
'Either we change the formula or we try to exclude those practices and find another way of rewarding them fairly,' he said.
'If we change the formula then you often find that the new solution does things you don't expect. If we exclude these practices from the formula, how do you reward them fairly? There is no obvious or simple solution here.'
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