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LEEDS MEDICAL STATISTICS GROUP SEMINAR The next seminar in our series will be: Prof. DEBORAH ASHBY from St Bart's & the Royal London MDS. "Casting a sceptical eye over the data: implementing Bayesian data monitoring in cancer clinical trials" 2pm, Friday 5th February, 1999. Abstract: Many clinical trials organisations use regular interim analyses to monitor the accruing results in large clinical trials. Classical rules, such as the group-sequential procedures of Peto, O'Brien and Fleming or Pocock have traditionally been based on P-values. However, none of these rules formally assess the impact that the results of a clinical trial might have on clinical practice. Thus a trial might be terminated early because of apparent treatment benefit, but fail to influence future clinicians to modify their future treatment policy. Bayesian rules have been proposed that have the potential to overcome these difficulties (Freedman, Spiegelhalter and Parmar, Statistics in Medicine, 1994). Like many Bayesian techniques, they were originally presented as reanalyses of trials that have already been published. They are now being used `live' (Fayers, Ashby and Parmar, Statistics in Medicine, 1997). We present details of their implementation in a trial of surgery with and without pre-operative chemotherapy for oesophageal cancer. Practical issues encountered will be discussed, including the choice of prior distribution and `clinically relevant' values for use in monitoring, and presentation of ideas to clinical members of the data monitoring committee. As one clinician put it `It's just casting a sceptical eye over the data'. Seminars are held at 34 Hyde Terrace, Leeds University. Everybody welcome. Further details and directions are available from Darren Greenwood. Email: [log in to unmask] Phone: 0113 233 4831 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%