Background: Individual participant data (IPD) have been used in many systematic reviews of randomised controlled trials. Commonly-cited benefits include the ability to perform meta-analyses of time-to-event outcomes, the ability to undertake subgroup analyses and to ensure data quality. Many published IPD reviews have involved large collaborative groups and large numbers of studies. We report the unique benefits of IPD in a small-scale review in ophthalmology.
Methods: Systematic review of studies comparing internal limiting membrane (ILM) peeling during macular hole surgery versus no peeling.
Results: IPD were received from the three identified fully-published studies. The authors of a fourth study were not willing to provide data until full publication but limited data were available from an abstract. The review was able to answer key questions about the effectiveness of ILM peeling. Benefits of IPD in this review included the ability to standardise the unit of randomisation (eye or patient), to include only randomised participants in one study with an unusual format, to explore timing of assessments, to include information from both IPD and published data, to conduct subgroup analyses by stage of macular hole and to conduct adjusted analyses controlling for study, size and duration of the macular hole.
Conclusions: This was a successful collaboration and a review of published data alone would have been very difficult. The benefits, however, were very different to those in a previous large-scale IPD review conducted by the primary author. In particular, the ability to standardise the unit of randomisation was crucial to the success of this review. This project demonstrates that there may be a variety of reasons to seek IPD, even in smaller systematic reviews.