Individual patient data (IPD) meta-analysis is a specific type of systematic review. Rather than extracting data from study publications, the original research data are sought directly from the researchers responsible for each study. These data can then be re-analysed centrally and combined, if appropriate, in meta-analyses.

IPD reviews usually require dedicated staff and would be difficult to do in ‘free time’. The approach requires particular skills and usually takes longer and costs more than a conventional systematic review of published or other summary data. However, IPD reviews offer benefits related particularly to the quality of data and the type of analyses that can be done (Stewart and Tierney 2002). For this reason they are considered to be a ‘gold standard’ of systematic review

IPD reviews have produced definitive answers to clinical questions, which might not have been obtained by standard systematic review methodology.