Background: Guideline development often requires the consideration of a large body of evidence, including many subgroups and outcomes. In such situations, systematic review authors may face trade-offs between rigor and feasibility. We confronted this situation in conducting a systematic review addressing the health effects of red meat consumption to inform a nutrition guideline.
Methods: Initially, we planned to include all randomized trials and observational studies reporting on the health effects of red meat. A preliminary search suggested that there would be more than a thousand articles meeting our eligibility criteria. We considered restricting eligibility on the basis of the number of included participants or study designs at lower risk of bias. Ultimately, we chose to include all randomized trials and cohort studies enrolling at least 1000 participants. We also refined our outcomes and subgroups of interest to make the review as manageable as possible, while still retaining all information that would be useful to the panel in making recommendations. As an example, with consensus of the guideline panel, we chose to only extract data on cancer outcomes with hypothesized associations with red meat consumption, rather than all cancer outcomes that we had initially intended to present. We also chose to restrict abstraction of data on surrogate outcomes to randomized trials.
Results: Of 10,406 references retrieved for title and abstract screening, we selected 1393 for full-text screening, of which 443 proved eligible. Data abstraction for these references is in progress and with the modifications we have instituted, has proved manageable. We will present our experiences in managing this large systematic review, including problems we have encountered and our approaches in dealing with them with the objective of maintaining high methodological rigor despite the size of the review.
Discussion: With exponential growth in the number of publications, more researchers are likely to find themselves conducting very large systematic reviews. While a plethora of methodological guidance exists for systematic reviewers, our work augments what to now has been limited guidance on dealing with the logistical challenges of very large reviews.
Patient/healthcare consumer involvement: Public representatives were involved in developing the research questions.