In this week's BMJ, Westaby and colleagues compare the value of two sources of data for determining mortality 30 days after congenital cardiac surgery—hospital episode statistics (HES) and the central cardiac audit database.1 They find that the central cardiac audit database is more complete than HES, but that individual centres need investment to improve the completeness and accuracy of their data. Their investigation follows a study published in the BMJ in 2004 that used HES to compare mortality from congenital heart surgery in different UK centres.2 The study suggested that Oxford had significantly higher mortality than the national average, and the results were reported widely by the media. So have we learnt anything new about the relative value of routinely collected versus specifically collected sources of data?

Routinely collected patient data are regularly analysed to investigate outcome. …