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Systematic, Scoping, and Rapid Reviews

Searching for Studies

A search for a systematic or scoping review aims to be objective, comprehensive (as much as possible within the limits of resources and time) and reproducible. Usually, the goal is to locate all published and unpublished literature that is relevant to your research question.

The process is iterative, usually beginning with preliminary searches to become familiar with key articles and the terminology used in the literature. Preliminary searches inform the development of a detailed database search strategy that is developed for one database and then translated for other databases.

Librarian Expertise

Librarians are trained in information retrieval and have the expertise needed to construct comprehensive searches for systematic and scoping reviews. Research has shown that librarian involvement in systematic reviews results in higher quality searches and reporting (Koffel, 2015; Meert, Torabi & Costella, 2016; Rethlefsen et al., 2015). Chapter 4 of the Cochrane Handbook advises that "review authors should work closely, from the start of the protocol, with an experienced medical/healthcare librarian or information specialist" (Cochrane Handbook, Chapter 4).

Librarian support for systematic and scoping reviews at Memorial

Database Searching

Begin with a preliminary search of one or two databases to learn the terminology used in the literature as well as key studies, authors, etc.

Develop the preliminary search into a detailed search strategy for one database.

Break your research question into main concepts and write a search strategy that uses both text words and subject headings (if available in that database) combined using Boolean (logic) operators (AND, OR, NOT).

  • Text Words - words or phrases that you expect to appear in the title, abstract, or elsewhere in the item record
    • Phrase searching - put phrases in quotation marks to search for terms together instead of separately e.g. "medical student"
    • Truncation / Wildcards - use an asterisk after part of a word to find words with alternate endings. e.g. teach* finds articles with teach, teaches, teaching, teacher, teachers.
  • Subject Headings - words chosen from a controlled vocabulary (database thesaurus) to describe the themes of the article. Subject headings vary across databases. Some databases do not have subject headings.
  • Boolean operators - terms used to connect parts of your search (AND, OR, NOT)
    • AND - used to combine different concepts; finds articles that mention both of the terms  e.g. (students AND exercise)
    • OR - used to join synonyms or related terms; finds articles with one or more of the terms listed e.g. (teacher OR educator)
    • NOT - used to exclude articles that mention a specific term e.g. (nursing NOT breastfeeding). Using NOT in systematic or scoping review searches is generally not recommended as it can cause you to miss relevant articles that mention a term in passing.
  • Parentheses - put search terms for each concept in parentheses e.g. (teach* OR educat*) AND (exercis* OR sport*)
  • Proximity/ Adjacency Searching - some databases allow you to search for terms near each other (syntax for proximity searching varies widely across databases) e.g. clinical* adj3 deteriorat*

Search Filters

Search filters (also known as hedges) are search strings designed to find specific selections of records, such as studies on a specific population (e.g., adult studies only) or studies with a specific design (e.g., randomized controlled trials). Some filters have been validated (tested against a gold standard), and some have not.

If you use a search filter, always report this in your methods and cite the source of the filter.

Sources of Search Filters

Search Peer Review

It is good practice to have your search strategy peer reviewed. The PRESS (Peer Review of Electronic Search Strategies) Guideline was developed for librarians to use when peer-reviewing librarian-authored searches:

Usually, the draft search for one database is peer reviewed so that any necessary changes can be made before translating the search for other databases.

Translating Your Search

Once you have a complete search for one database (ideally peer reviewed), translate the search for each additional database to be searched. This involves revising the search syntax (field tags, truncation symbols, etc) and checking for equivalent subject headings in each database thesaurus (if applicable).

Polyglot Search is a tool that can assist with search translation from PubMed or Ovid MEDLINE to other databases, but it is still imperative that you familiarize yourself with the syntax of each database and double check the search strings for accuracy.

Grey Literature

Grey literature is literature that is not formally published. It includes documents such as dissertations, reports from governments or organizations, working papers, conference abstracts or proceedings, clinical trial documentation, and more.

Depending on the research question, searching sources of grey literature can help to ensure a more comprehensive review.

Potential information sources for finding grey literature

Other Search Methods

In addition to database and grey literature searching, a variety of supplementary search methods may be employed to ensure comprehensive coverage in a systematic or scoping review.

Citation Searching

It is common to review the reference lists of all included studies, and sometimes other systematic reviews on the same topic, to check for studies that may have been missed. This is known as backward citation searching. It can be done manually or using a citation index.

Similarly, some review teams search for newer papers that have cited the studies included in the review. This is known as forward citation searching.

Citation searching can be done using one of the following citation indices:

Handsearching

Handsearching refers to manually reading through the tables of contents of print journals to identify additional relevant studies. This is rarely done by hand anymore, now that most journals are searchable online, but it can be a useful process if a specific journal has been identified that is not indexed in any of the databases you have searched.

Documenting and Reporting Your Search

Be sure to document the search in detail, including:

  • each database searched, the platform used, and the date last searched
  • the details of other searches undertaken, such as trial registries, websites, citation searching, etc.
  • the line-by-line search strategy for every database and other sources searched
  • any limits or filters used
  • any peer review process
  • the number of results from each database and other sources searched
  • the number of duplicates identified and removed and the process used

PRISMA-S Search Reporting Guideline

PRISMA-S is an extension to the PRISMA Statement for Reporting Literature Searches in Systematic Reviews. It is 16-item checklist that covers multiple aspects of the search process for systematic reviews.