A protocol is a road map for your review. It should contain detailed descriptions of your hypothesis, anticipated data sources, data extraction, appraisal tool, team responsibilities, methodology, etc.
Creating a protocol at the beginning of a process adds to transparency and reduces bias by ensuring the review was planned ahead of time. Planning ahead increases the likelihood of adhering to the methodology and reduces the potential for HARK (Hypothesis After Results are Known). Planning ahead also helps the team anticipate challenges, develop workflow, and identify team needs well in advance.
A protocol strengthens the review by requiring teams to clearly state their hypotheses, what new knowledge they hope to generate, and other elements such as a group's working hypothesis, inclusion/exclusion criteria, funding sources, how the team will screen data, etc. By clearly stating and adhering to the research goals and methods, protocols help teams reduce potential bias.
Apart from clearly setting expectations for the team, a well built protocol should give a team a head start on writing their manuscript, because all the things described in a protocol are also foundational parts of a systematic review.
While it is not expected that teams conducting scoping reviews create protocols, it is useful for scoping review teams to create one for the same reasons.
Registering a protocol is important because a registered protocol can help teams avoid duplicating the exact same review question, or build the potential for collaboration between teams on similar projects.
Links for non-health sciences projects