A systematic review of core outcome set development studies demonstrates difficulties in defining unique outcomes

Abstract

ObjectivesCore outcome set (COS) development often begins with a systematic review to identify outcomes. Reviews frequently show heterogeneity in numbers of outcomes reported across trials. Contributing to this is a lack of a uniform definition for an outcome. This study proposes a first working definition for a unique trial outcome to support reporting a quantitative assessment of outcome reporting heterogeneity (ORH). Study Design and SettingEligible COS literature (development papers, protocols, and reviews) were identified using the COMET database, Ovid MEDLINE, and PubMed. Outcome numbers, definitions, timing, and grouping methodology were examined. ResultsOne hundred and thirty two studies were included. 82 (88.1%) studies (excluding protocols) reported a total number of unique outcomes (median, 82; range, 12-5776; IQR, 261). Timing of assessment was reported in 32 (31.4%) studies. Methods to group similar outcomes were reported in 8 (7.8%) articles. No study defined how outcomes were agreed as different and how final numbers of unique outcomes were determined. It is proposed that a unique outcome requires original meaning and context. Thus ORH is suggested to be the reporting of multiple unique outcomes across trials related to one health care condition. ConclusionThis review identified inconsistencies in how authors define, extract, group, and count trial outcomes. Further work is needed to refine our proposed definitions to optimize COS development and allow a quantifiable measure of ORH.