Assessing the magnitude of changes from protocol to publication—a survey on Cochrane and non-Cochrane Systematic Reviews

OBJECTIVE: To explore differences between published reviews and their respective protocols in a sample of 97 non-Cochrane Systematic Reviews (non-CSRs) and 97 Cochrane Systematic Reviews (CSRs) in terms of PICOS (Patients/Population, Intervention, Comparison/Control, Outcome, Study type) elements and the extent to which they were reported. STUDY DESIGN AND SETTING: We searched PubMed and Cochrane databases to identify non-CSRs and CSRs that were published in 2018. We then searched for their corresponding Cochrane or PROSPERO protocols. The published reviews were compared to their protocols. The primary outcome was changes from protocol to review in terms of PICOS elements. RESULTS: We identified a total of 227 changes from protocol to review in PICOS elements, 1.11 (Standard Deviation (SD), 1.22) changes per review for CSRs and 1.23 (SD, 1.12) for non-CSRs per review. More than half of each sub-sample (54.6% of CSRs and 67.0% of non-CSRs) (Absolute Risk Reduction (ARR) 12.4% [−1.3%; 26.0%]) had changes in PICOS elements. For both subsamples, approximately a third of all changes corresponded to changes related to primary outcomes. Marked differences were found between the sub-samples for the reporting of changes. 95.8% of the changes in PICOS items were not reported in the non-CSRs compared to 42.6% in the CSRs (ARR 53.2% [43.2%; 63.2%]). CONCLUSION: CSRs showed better results than non-CSRs in terms of the reporting of changes. Reporting of changes from protocol needs to be promoted and requires general improvement. The limitations of this study lie in its observational design. Registration: https://osf.io/6j8gd/.