This is an archived version of the Handbook. For the current version, please go to or search for this chapter here.

4.7.1  References to studies

Studies are organized under four fixed headings. Each of these headings can include multiple studies (or no studies). A study is identified by a ‘Study ID’ (usually comprising the last name of first author and the year of the primary reference for the study). A year can be explicitly associated with each study (usually the year of completion, or the publication year of the primary reference), as can identifiers such as an International Standard Randomised Controlled Trial Number (ISRCTN). In addition, each study should be assigned a category of ‘Data source’ from among the following:

Each study can have multiple references. Each reference may be given identifiers such as a MEDLINE ID or a DOI. One reference for each study should be awarded the status of ‘Primary reference’.


Authors should check all references for accuracy.

Included studies

Studies that meet the eligibility criteria and are included in the review.


Excluded studies

Studies that do not meet the eligibility criteria and are excluded from the review.


Studies awaiting classification

Relevant studies that have been identified, but cannot be assessed for inclusion until additional data or information are obtained.


Ongoing studies

Studies that are ongoing and meet (or appear to meet) the eligibility criteria.