Studies are organized under four fixed headings:
Studies that meet the eligibility criteria and are included in the review.
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.
Studies that are ongoing and meet (or appear to meet) the eligibility criteria.
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:
Published data only;
Published and unpublished data;
Unpublished data only;
Published data only (unpublished sought but not used).
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.