Meta-analyses using individual patient data

Systematic reviews of randomized controlled trials often provide the most reliable information on which to base treatment policy. However, to be reliable, such reviews need to contain a high proportion of all the relevant randomized evidence. This relates both to the need to find all trials and the need to analyse data on all participants. One way to achieve this is through a collaboration in which those responsible for the trials supply data on each randomized patient for an individual patient data meta-analysis. However, such projects require more time and resources than more conventional reviews and are still rare. This paper illustrates how they can help to achieve the aim of using complete data in a systematic review.