Implementation science research priorities for Universal Health Coverage:Methodological lessons from the design and implementation of a multi-country modified Delphi study

Delphi studies are rapidly gaining prominence in global health research. However, researchers' modifications to the Delphi method are often not well-described or justified, limiting opportunities to systematically learn from these studies when the methods are applied to other topics and settings. This paper aims to describe an approach to implementing a modified Delphi study and reflect on the research process in the context of a multi-country study of implementation science research priorities to advance Universal Health Coverage (UHC). We review trends in the use of the modified Delphi method in global health research, outline our three-phased modified Delphi approach, and share reflections on five decision points for implementing the study: 1) identifying and recruiting participants for the expert panel, 2) addressing participant attrition between rounds, 3) justifying the most appropriate cutoff points, 4) incorporating new items raised by participants in open-ended survey sections, and 5) ensuring maximum variation in perspective in the panel of experts. Insights from this work foster greater understanding of the underlying assumptions for, and interpretation of, 'modified' in modified Delphi studies. This study will encourage critical dialogue about points of methodological contention in Delphi methodology and thus, are relevant for scaling the use of modified Delphi studies in public health, including global health research.