Objective 　① To document the way in which allocation concealment is described and coded for studies included in Cochrane Reviews.②To feed back any gaps or miscodings to individual review groups.③ To suggest changes and expansions to advice on how to code and describe allocation concealment methods.
Methods 　The coding and description of methods of allocation concealment for studies included in all 1 596 reviews on issue 1, 2003 of The Cochrane Library are being extracted.So far results are available for 10.8% (173/1 596) of reviews containing 1 844 studies, from 10 Collaborative Review Groups (CRGs).Discrepancies, and inconsistencies with the Cochrane Reviewers’ Handbook, are being documented and analysed.
Results 　The current coding of the adequacy of allocation concealment in studies included in Cochrane reviews is not likely to be very accurate.This is due to failure to describe methods of allocation concealment (38.6% of the sample of 1 844 studies) as well as miscoding (at least an additional 9.2%).The most common method for studies coded A was some variation of envelope use (133/675-19.7% of all A codes). The most common "method" for studies coded B was method unclear or not described in the report of the study (426/665, 64% of all B codes).
Conclusions 　Since adequate allocation concealment is so important in protecting against bias in randomised controlled trials, it needs to be accurately coded and described.We need to improve how this is done for studies included in Cochrane Reviews.Since over half the studies coded as D were likely to have been where reviewers omitted to enter a code, the default should be changed from D to "code not supplied".Structural changes to RevMan are suggested-ideally the addition of a separate new study quality assessment table with fixed headings as well as the facility to enter free text.Suggestions for improving coding in particular reviews will be fed back to CRGs in the next stages of this project.Suggestions for additions to the Cochrane Reviewers’ Handbook are also made.

Citation： Philippa Middleton. How Allocation Concealment Is Handled in Cochrane Reviews. Chinese Journal of Evidence-Based Medicine, 2004, 04(10): 711-713. doi: Copy