We thank Dr Ch’ng et al for their interest in our article.1 They raise an interesting point concerning retrospective and prospective studies. We acknowledge in our paper that the study methods we used were different from those used in the original single-centre study by Ch’ng et al. However, we do not agree that our study was retrospective.

UKOSS has a planned programme of studies2; participating clinicians at the 226 collaborating hospitals receive notification of this programme with individual study documentation before the commencement of any study and are asked to identify cases prospectively (ie, in the future). We do ask for retrospective reporting of the clinical details of cases clinicians have prospectively identified, and this is wholly different in methodology from the retrospective study originally conducted by Ch’ng et al. Furthermore, we do not believe that this …