Meta-analyses that are based on individual patient or participant data (IPD) use the same basic approach as any other well-conducted systematic review and meta-analysis. However, they involve the collection of the original data from all the relevant trials worldwide. This means trial groups need to be persuaded to supply their trial data, and these data need to be prepared and checked before being included in the meta-analysis. Therefore, to succeed, an IPD meta-analysis relies on extensive collaboration between researchers. It also takes more time and resource than a meta-analysis based on results extracted from published trial reports. However, the IPD approach can improve the quality of both the data and the analyses and so the reliability of the results. Therefore, it is considered the gold standard.
IPD meta-analyses are less common than other types of systematic review. They were first used to summarise the effects of treatments for cardiovascular disease and cancer. They are now used in a range of healthcare areas e.g. to examine the effects of treatments for Alzheimers disease, dyspepsia, epilepsy, malaria, HIV infection and hernia.
The CTU Meta-analysis Group is one of only a few groups worldwide that regularly does IPD meta-analyses. Practical guidance on IPD meta-analysis published by the Group is listed below. Further information on IPD meta-analyses can be found on the Cochrane Collaboration IPD Meta-analysis Methods Group website.
For our current methodological research relating to IPD meta-analysis see CTU Hub for Trials Methodology Research.
General IPD meta-analysis references
Stewart, L. A., Tierney, J. F. and Clarke, M. (2008) Reviews of Individual Patient Data, in Cochrane Handbook for Systematic Reviews of Interventions: Cochrane Book Series (eds J. P. Higgins and S. Green), John Wiley & Sons, Ltd, Chichester, UK. doi: 10.1002/9780470712184.ch18
Stewart LA, Tierney JF.
To IPD or Not to IPD? Evaluation & the Health Professions 2002;25(1)76-97. Read the abstract
Stewart LA, Clarke MJ, on behalf of the Cochrane Working Party Group on Meta-analysis using Individual Patient Data. Practical methodology of meta-analyses (overviews) using updated individual patient data. Statistics in Medicine 1995;142057-79. Read the abstract
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