This policy covers the reporting of search dates in Cochrane Reviews. It is informed by guidance on re-running searches covered in MECIR conduct standard C37. This standard requires that searches for all relevant databases be run (or re-run) within 12 months before publication of the review or review update, and that the results are screened for potentially eligible studies.
For definitions of search types (full, top-up, scoping) see Table below.
- Updates vs. amendments: a review is considered updated and receives a new citation in Cochrane Database of Systematic Reviews (CDSR) when a new search is conducted and the results of the search are fully incorporated. If a scoping search is conducted to determine if an update is required, then the date of this search will not change the 'Date of search' in the review or lead to a new citation version being created. This should be published as an amendment if necessary; see Assigning ‘What’s New’ events to Cochrane Reviews.
- If top-up searches are performed and the results incorporated then that top-up search date becomes the date of the full search (i.e. the date that appears in the ‘Date of Search’ field).
- If top-up searches are performed and the results are NOT fully incorporated then:
- The ‘Date of search’ remains the date of the search for which results were fully incorporated.
- Studies not yet fully incorporated into the review are added to ‘Studies awaiting classification’.
- The 'Search methods' in the abstract should focus on reporting the search dates related to the last fully incorporated studies. Brief mention of a top-up search may be made only if it was conducted for a completed update or new review. Do not refer to scoping searches for updating in the abstract.
- The 'Search methods for identification of studies' in the main text of the review should be used primarily to describe the details of the search for which the results have been fully incorporated, i.e. the dates of individual database searching and the hits retrieved should be based on the search date where results are fully incorporated. If a top-up search has been performed, but the results not yet fully incorporated, the search section may briefly describe this (see example below) and state how many studies have been placed in 'Studies awaiting classification'.
- In the 'Results of the search' section the authors should specify the number of studies yet to be fully incorporated into the review. This should also be reflected in the conclusions (both of the main review and the abstract).
- The PRISMA flow of studies diagram should also reflect the number of studies in the 'Studies awaiting classification' section.
- The 'What’s New' events must describe the number of studies that have been put into 'Studies awaiting classification' if the top-up search is mentioned in the search methods section.
- The search appendix should present only database strategies for searches conducted for which results were fully incorporated.
- If different databases were searched on different dates, the most recent date of the search for each database should be given within the text of the review and the earliest of these dates should be entered as the ‘Date of Search’. In the case of review updates or 'top-up' searches, if there is clear rationale for not searching one or more of the previously searched databases (e.g. because no unique relevant records were identified in the original/previous search, or the database is no longer being updated), the rationale should be stated within the text of the review. In this case, the 'Date of search' should be the earliest date of the searches performed for this smaller set of databases.
Definitions of search types (full, top-up, scoping)
Full search – results fully incorporated
Electronic search strategies run in full in all relevant databases AND all search results are assessed for eligibility as included, excluded, or ongoing studies. Only if all reasonable efforts to classify search results have failed should they be placed in ‘Studies awaiting classification.’*
Top-up search – results not fully incorporated
Electronic search strategies run in full in all relevant databases BUT search results are not all assessed for eligibility, instead they are placed in 'Studies awaiting classification'.
Scoping search for updating
Electronic search strategies run in selected databases to determine if an update is required.
|*See R6 and R34 in MECIR; and definition of updating.|
Examples of reporting top-up searches
The number of instances where a top-up search is performed and potential new studies are identified but not fully incorporated before publication should remain low. The following examples show how such searches should be described in various sections of a systematic review:
Do not change the 'Date of search' or the 'Assessed as up-to-date' (see Note for editorial base staff) in the Cochrane Review 'Information’ section. Also, if less than 10 trial reports then list here in parentheses and link. For example:
"The search was updated in month/year and n trial reports added to ‘Studies awaiting classification’ (e.g. Bertini 2005; Crowther 2005; Gillen 2004)."
The focus should remain on the text about previous searches (fully incorporated) but the top-up search may be mentioned. For example:
"We searched the Cochrane Central Register of Controlled Trials, MEDLINE, Embase, and CINAHL (June 2013). We updated this search in September 2014, but these results have not yet been incorporated."
Search methods for identification of studies
The search should be reported as per MECIR reporting standards R34 to 39, including the dates for each source. At the end of the search methods section, it is appropriate to add the following text:
"We performed a further search in [month/year]. Those results have been added to 'Studies awaiting classification' and will be incorporated into the review at the next update."
Do not list all databases and the dates. If a top-up search in reported in this section, only a single month (or range of months) and year should be shown.
Results: Description of studies
This section will differ depending on the review, so add text where it is most appropriate); for example:
"[insert number] study reports from an updated search in [month/year] have been added to 'Studies awaiting classification'."
Discussion: Potential biases in the review process
Acknowledge the potential impact of un-incorporated studies as a source of potential bias, especially if studies concerned are potentially important in terms of sample size or direction of effect; for example:
"We attempted to conduct a comprehensive search for studies, but the fact that [insert number] studies have not yet been incorporated may be a source of potential bias."
Authors’ conclusions (Implications for practice)
This is not an implication for practice as such, but users should be alerted to the issue of un-incorporated studies, particularly if the studies concerned are potentially important in terms of sample size or direction of effect; for example:
"The [insert number] studies in 'Studies awaiting classification' may alter the conclusions of the review once assessed."
Note for editorial base staff
One date should be used to reflect the search and full incorporation of all search results into the review; this date is the ‘Date of search’. Standard practice has been to publish the 'Assessed as up-to-date' field and not the 'Date of search'. Until the 'Assessed as up-to-date' field is removed from RevMan these two dates must be the same. If these fields have been completed by a member of the author team, editorial base staff must check that there is agreement between dates.