"Decisions about which studies to include in a review are among the most influential decisions that are made in the review process and they involve judgement" (Lefebvre et al., 2022, s. 4.6.4).
The inclusion and exclusion criteria for the review are usually developed in the planning stage, and are documented in the protocol, if you are using one. They guide you on choosing which of the studies you found will be included and analysed in the review, and help reduce selection bias. It is important to keep records of how many articles were left after each stage of screening to accurately report your process.
It is considered good practice, and is a requirement of some review types, such as systematic reviews, to have more than one person involved in screening articles to reduce the risk of bias. Disputes can be resolved by consensus, or asking another team member.
The screening takes place in stages:
In this stage, you look at the title and abstract of all articles found to remove obviously irrelevant articles. You do not need to provide reasons why you excluded them at this stage, although you do need to keep track of how many were excluded.
In the second stage, you will need to read the full text of each remaining article to assess it against the inclusion and exclusion criteria. You will need to keep records of any reasons for excluding articles, such as lack of relevance to the research question or not the desired population studied.
When you conduct the full text screening of the results, you may find that you are unable to access the full text. In this case, you can contact your liaison librarian, or place a request through Document Delivery.
This final stage is often only included in systematic reviews or meta-analyses, although it may be part of other review types depending on the aims. In this stage, formal assessments of quality and/or risk of bias is undertaken, using standard evaluation tools and checklists, which aids reporting and replication. It is done by more than one member of the research team and only articles agreed on are included. External validity is also assessed, or generalisabilty and applicability.
The following websites have sets of critical appraisal tools for a range of different study types that can be used.