The Umbrella review protocol should describe the process of study selection for all stages of selection (based on title and abstract examination; based on full text examination) and the procedures for solving disagreements between reviewers. Selection is performed based on inclusion criteria pre-specified in the review protocol. For any systematic review, study selection (both at title/abstract screening and full text screening) is performed by two or more reviewers, independently. Any disagreements are solved by consensus or by the decision of a third reviewer.