Which general practices have higher list inflation? An exploratory study

Background. There is a 7% discrepancy between English population estimates based on census figures and those based on the registered lists of GPs. GP income under the 2004 new contract will be based on registered patient populations but a national 'de-ghosting' exercise will ensue, aiming to eliminate list inflation. Objective. To derive an estimate of the variation in list inflation between individual general practices. Methods. Letters were sent to all men aged 20-29 years and registered at practices based in three inner city Primary Care Trusts (n = 42 712). Non respondents received one further reminder. Cards were issued to each GP listing non responders. Patients were deducted from the GP list after six months if the GP did not verify the address. Results. 42 712 letters were sent. 33.5% of registered patients were eventually deducted from the GP list (deduction figures only available for 20-24 year old group). Practice level deduction rates ranged from 7-76%. Practices with higher deduction rates achieved lower vaccination rates for 2 year olds (Pearson's r = 20.25; P = 0.005) and cervical smear rates (Pearson's r = 20.18; P = 0.04); they also had cheaper prescribing costs per ASTRO-PU (Pearson's r = 20.20; P = 0.03). Conclusions. If these findings apply to the whole registered population, the national de-ghosting exercise is likely to result in large changes to the list size of some practices. Without correcting for list inflation, primary care research based on patient list size as the denominator may underestimate various measures of GP activity, particularly in deprived inner city areas. Resource allocation is also likely to be distorted by differences in list inflation.