A mixed methods study of researchers’ experiences of developing core outcome sets

Background A systematic review of core outcome sets (COS) identified 198 COS [1]. A range of methods were used to develop COS. Furthermore, 164/178 studies that described the methods used did not provide an explanation regarding their choice of methodology. There is little guidance about how to conduct or report COS studies and it is currently uncertain which of these methods are the most suitable, feasible and efficient. It is important to investigate COS developers’ choice of approach as this is a new area of research, and in order to formulate guidance in this area we need to try and understand the current situation, including the influences of methodological choices being made.