Background: Selective reporting in trials can affect conclusions of systematic reviews. The Outcome Reporting Bias in Trials (ORBIT) tool was developed to help researchers to identify sources of selective reporting: i.e. when not all analysed outcomes are reported, selective reporting of a specific outcome, and, incomplete reporting of a specific outcome (Kirkham 2010). Its use in systematic reviews helps readers to judge reporting bias better.
Objective: To describe the use of ORBIT classification in Cochrane Systematic Reviews.
Methods: We used the search strategy ["outcome reporting bias in trials" OR "ORBIT tool" OR "ORBIT study"] in the Cochrane Library to identify protocols and publications that performed or plan to perform the ORBIT classification. We conducted descriptive statistics to describe study characteristics.
Results: We identified 68 studies. We double checked all studies to assure the ORBIT classification was planned or used. From those, four studies were excluded and while 14 studies mentioned assessment of outcome reporting bias in trials they did not specify the use of ORBIT for this purpose. There were 29% (4/14) reviews and 71.4% (10/14) protocols. Therefore, 50 studies were included in analysis as they mentioned the ORBIT classification, 54% (27/50) were reviews and 46% (23/50) were protocols. The review groups that adopted the ORBIT classification were Cochrane Metabolic and Endocrine Disorders 54% (27/50), Cochrane Epilepsy 28% (14/50), Cochrane Eyes and Vision 10% (5/50), and Cochrane Musculoskeletal 8% (4/50). There are a growing number of publications using ORBIT classification over time (see Graph 1).
Conclusions: There is a timid growth in the number of Cochrane Review Groups adopting the ORBIT classification in Cochrane Reviews over time. Thus, efforts to disseminate the use of this tool are needed to provide transparent conclusions regarding selective reporting bias.
Reference: Kirkham JJ, Dwan KM, Altman DG, Gamble C, Dodd S, Smyth R, Williamson PR. The impact of outcome reporting bias in randomised controlled trials on a cohort of systematic reviews. BMJ 2010;340:c365. doi: 10.1136/bmj.c365