In many databases it is possible to limit the search using built-in limiting options, such as language, year of publication, and peer-reviewed. Depending on a database other limiting options, e.g. age group or publication type, can also be available. When undertaking a search for a systematic reviews, be careful in using the limits so that relevant articles are not left out.
By using these limiting options, it is also possible that the most recent studies might not be found; this is because their details might not yet been fully entered into databases. The reporting and reproducibiity of the search strategy also suffers from the use of limiting options, as the database algorithms are not transparent, i.e. we do not know for certain what exactly the search engine is doing.
NOTE. In a systematic review, all limiters must be defined before the search is undertaken, and described in the protocol. You also need to be consistent when applying the limits.