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Dear Colleagues, Would anyone be prepared to respond to this query from Gayle Robins. All good wishes, Olive >>> "Robins, Gayle" <[log in to unmask]> 09/05/2007 06:01 >>> Hello Mrs Goddard When I evaluate a clinical trial, I use the Oxford Centre for Evidence Based Medicine's recommendation as a guideline for whether the information provided by the trial could be considered as best evidence. I note that individual randomised controlled trials with narrow confidence intervals are considered as level 1b on your levels of evidence chart. Please can you advise me where, if at all, subgroup analyses of these level 1b randomised clinical trials would fall on the best-evidence hierarchy. I realise that there are many different types of subgroup analysis: those that are defined apriori versus retrospectively or on an ad-hoc basis; those that address the same outcome of interest that the randomised controlled trial was designed to assess versus other outcomes; and those that are part of a plethora of subgroup analyses of the same trial and so require correction for multiplicity, to name a few. Are any subgroup analyses of level 1b randomised controlled trials ever considered best evidence? Thanks you for your time taken to read this email. I would appreciate any advice that you can give me, or people that I could contact, in this regard. Gayle Robins Team Leader Clinical Trials Insight Adis International Wolters Kluwer Health Ph: 09 4770700 Email: [log in to unmask]