An important part of the SR process is defining what will and will not be included in your review.
Inclusion and exclusion criteria are developed after a research question is finalized but before a search is carried out. They determine the limits for the evidence synthesis and are typically reported in the methods section of the publication. For unfamiliar or unclear concepts, a definition may be necessary to adequately describe the criterion for readers.
Some examples of common inclusion/exclusion criteria might be:
*note of caution: research is published all over the world and in multiple languages. Limiting to just English can be considered a bias to your research.
Empty reviews are when no studies meet the inclusion criteria for a SR. Empty reviews are more likely to subject to publication bias, however, they are important in identifying gaps in the literature.