Data collection

Data collection, collation and verification are time-consuming aspects of any systematic review or meta-analysis. For those that use data extracted from published reports, several weeks may be required to allow time to read each paper carefully and extract the appropriate data. This stage may take many months for those that use IPD. The trialists need to be contacted and invited to provide the desired information. The data then need to be transferred checked and verified before any analyses can be done. The value of writing a clearly specified protocol (see Section 11.5.2) cannot be over-emphasized, as collecting the wrong data or finding out that additional information is required during the data collection phase can be both costly and time-consuming. Thus, a clear idea of what questions maybe reasonably addressed, which endpoints will be used and usually a clear idea of how any final analyses will be organized is an essential precursor to data collection.

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