The use of the NHS Central Register when estimating patient survival

National and international comparisons of survival of patients are hampered by the bias introduced when different sources of data are used to confirm a patient's continuing survival. Three methods are proposed for processing survival data which, when used in conjunction, will provide limits for the extent of this bias. Using data on heart valve replacement patients it is shown that the use of the United Kingdom National Health Service Central Register, supplemented by data from routine hospital clinic visits, will lead to a maximum overestimate of survival of 1.7% over 10 years, and in practice the overestimate will be much less. It is proposed that for publications two survival curves should be calculated using the most favorable and unfavorable assumptions about patients "lost to sight". This will provide upper and lower bounds to the survival, the difference between these curves being dependent on the quantity of missing data.