Data extraction in meta-analysis

Extracting data for meta-analysis can be very frustrating because authors often don’t report the summary data that you want, that is, the same statistics and the right statistics for the meta-analysis software e.g. mean and standard deviation. There are some great resources for data extraction to help you convert data from what’s reported into what you want, but perhaps randomised trials are better served (for example, by the excellent Cochrane Handbook) than other study designs. There are other resources but they’re scattered around and are sometimes not accessible to all those who may want to carry out meta-analysis, as some methods involve complicated equations.

The aim of this blog is to provide a series of useful tips on data extraction, to shed light on, and raise awareness of the different methods and equations that are available to convert data into what you need for meta-analysis. I’ll also try to demystify the maths by giving worked examples and only offering the derivation of the equations as an optional extra.