References are divided into two groups: 1) references to studies; and 2) other references. The references to studies comprise included, excluded, and ongoing studies as well as studies awaiting classification. The other references comprise additional references (e.g. those used in the background or discussion sections) and references to other published versions of the review (including the protocol).
Each study has a Study ID (usually made up of the last name of the first author plus the year) used to refer and link to the study within the review. Each study has one or more references. Other references have Reference IDs (usually made up of the last name of the first author plus the year).