7.4.3  Individual patient data

Rather than extracting data from study publications, the original research data may be sought directly from the researchers responsible for each study. Individual patient data (IPD) reviews, in which data are provided on each of the participants in each of the studies, are the gold standard in terms of availability of data. IPD can be re-analysed centrally and, if appropriate, combined in meta-analyses. IPD reviews are addressed in detail in Chapter 18.