Accessibility statement

Individual Participant Data (IPD) meta-analysis

Systematic reviews with IPD meta-analysis have the same underpinning principles and follow many of the same procedures as conventional systematic reviews. For example, following a protocol that pre-specifies the methods to be used, having clear inclusion and exclusion criteria and comprehensive strategies for identifying eligible studies.

However, instead of extracting summary data (such as numbers of babies born before 37 weeks, or mean maternal age) from journal articles or trial reports, IPD meta-analyses centrally collect, validate and re-analyse individual-level data on each participant included in each included trial (such as the age of each individual woman and the gestational age at which her baby is born).

Individual-level data enables more powerful and flexible analysis, particularly for time to event outcomes and of potential effect modifiers - where we can explore whether there are particular types of individual who benefit more or less from the intervention being investigated. The IPD approach also provides opportunity to seek unpublished trials and updated follow-up, collect unreported outcomes and data from participants excluded from published analyses. Where differing measurement scales or instruments have been used these can sometimes be translated to common scores or measures enabling synthesis of data that could not otherwise be combined.