1 Assessment of Outcome Reporting Bias in Studies Included in Campbell Systematic Reviews: Protocol Authors Julia H. Littell 1 Dennis M. Gorman 2 Jeffrey C. Valentine 3 Therese D. Pigott 4 Affiliations 1 Graduate School of Social Work and Social Research, Bryn Mawr College, Bryn Mawr, Pennsylvania, USA 2 Department of Epidemiology & Biostatistics and School of Public Health, Texas A&M University, College Station, Texas, USA 3 Department Counseling and Human Development, University of Louisville, Louisville, KY, USA 4 School of Public Health, Georgia State University, Atlanta, GA, USA Contact person Julia H. Littell Email: jhlittell@gmail.com Address: 124 Grandview Rd., Ardmore, PA 19003 USA Contributions of authors: All members of the review team have expertise in the content area, systematic review methods, statistical analysis, and information retrieval. JL and DG conceived the idea for this project. JL drafted the protocol; DG, JV, and TP reviewed and commented on the protocol. Sources of support: None. Declarations of interest: JL, TP, and JV are co-authors of one or more published Campbell reviews. No member of the review team will be involved in screening or extracting data from any reviews they co-authored. Preliminary timeframe: The first draft of the review will be completed by September 2023. Plans for Updating this review: The review will be updated once every five years, if sufficient resources are available. All members of the review team will participate in updates, depending on their availability.