To IPD or not to IPD? Advantages and disadvantages of systematic reviews using individual patient data.

Systematic reviews and meta-analyses that obtain original research data on individual participants enrolled in trials have been described as the gold standard of review. However, they may take longer and be more resource intensive than other types of review. The authors describe potential advantages and disadvantages of the individual patient data (IPD) approach, including benefits from improved data quality, benefits afforded by the type of analyses that can be done, and advantages in achieving consensus around results and interpretation by an international multidisciplinary team. Disadvantages and barriers relating to resource and expertise, negotiating collaboration, and software requirements are also discussed. At the outset, reviewers should consider the methodological factors likely to influence results in their particular review setting, together with time and resource constraints, so that an active decision can be made about whether to extract data from published reports, collect additional or replacement summary data from trialists, or collect IPD.