You may want to think about criteria that will be used to select articles for your literature review based on your research question. These are commonly known as inclusion criteria and exclusion criteria. Be aware that you may introduce bias into the final review if these are not used thoughtfully.
Inclusion criteria are the elements of an article that must be present in order for it to be eligible for inclusion in a literature review. Some examples are:
Included studies must have compared certain treatments
Included studies must be experimental
Included studies must have been published in the last 5 years
Subject headings and keywords have different advantages and disadvantages. Keywords can retrieve new articles that do not yet have subject headings assigned to them. You can also use keywords to capture alternative spellings. Subject headings, however, will help you find highly relevant articles, and may mitigate the need to search for synonyms.
When you conduct your search, consider whether it makes sense to use keywords, subject headings, or both.
Exclusion criteria are the elements of an article that disqualify the study from inclusion in a literature review. Some examples are:
Study used an observational design
Study used a qualitative methodology
Study was published more than 5 years ago
Study was published in a language other than English