Writing a protocol

As with any formal clinical research, writing a detailed protocol is an essential first step in any systematic review. Developing a protocol makes a systematic review more rigorous as the methodology is specified at the outset. For example, rules concerning eligibility are made in advance of any results, and subset and subgroup analyses are pre-planned rather than ad hoc. Any deviations from the protocol should be explained in the completed review. Protocols are also valuable in helping to identify problems and clarify issues early in the project. A good protocol can also be invaluable in explaining and promoting the proposed review to potential collaborating trialists, serving to demonstrate the importance of the question, the appropriateness of methodology and competence of those undertaking the review, all of which can be important in persuading them to participate. Specifying inclusion criteria means that trials can be evaluated for suitability at an early stage. Although there may be a temptation to obtain data from all trials at the outset of the meta-analysis, a more measured approach makes it less likely that trials will have to be withdrawn or excluded after data have been prepared and provided. Time spent at this stage more than makes up for itself later, although it does mean that initiating collaborations maybe delayed. Box 11.2 shows some of the items that should be considered for inclusion in a systematic review protocol.

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