Abstract
Many retrospective observational studies have been published in the recent literature. In the current issue of this journal two papers deal with retrospective analysis of observations after different surgical interventions: one concerns surgery for hilar cholangiocarcinoma, the other surgery for oesophageal carcinoma. Studies of this design are hard to interpret due to a number of methodological issues: (a) cohort effects: both the patient population and diagnostic procedures may have changed over time; (b) the learning curve of the healthcare provider, in this case the surgeon; and (c) confounding by indication: the data studied is biased by medical decision-making. However, the results of these studies inform healthcare providers and patients about survival and complication rates, among other things. Although they are not properly designed according to basic evidence-based medicine guidelines, these studies still provide us with clinically relevant information about current experience of medical interventions.
