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EPIB 629 Knowledge Synthesis

Systematic searching

Systematic searching

Knowledge syntheses involve systematically searching the literature. For example,

Systematic reviews of interventions require a thorough, objective and reproducible search of a range of sources to identify as many relevant studies as possible (within resource limits). This is a major factor in distinguishing systematic reviews from traditional narrative reviews (...)

Higgins JPT, Green S (editors). Cochrane Handbook for Systematic Reviews of Interventions Version 5.1.0. The Cochrane
Collaboration, 2011. Available from http://handbook-5-1.cochrane.org/.

Systematic searching is:

  • Thorough: It involves searching more than one database and using a combination of textwords plus subject headings (the latter when available) to identify relevant literature. It also involves using supplementary search methods in addition to database searching
  • Objective: Search terms include variations in terminology and the searcher should avoid biasing the results of the search through the selection of search terms
  • Reproducible: The searcher is careful to record all the details of the search, including the database and platform with dates of coverage (may differ based on institutional subscriptions), the search strategy as executed, and the date the searches were run

Core databases

Selecting databases to search

Need help choosing which database to search? This table shows you the differences between the core databases used in health sciences knowledge syntheses. 

Need help searching the databases? Start with this introduction to searching with subject headings and keywords.

Database (Platform) Subject coverage Publication types included Dates covered
MEDLINE (Ovid) / PubMed Primary biomedical database for health care research; we recommend searching MEDLINE on the Ovid platform (enhanced options for searching) or via PubMed (free platform) Journal articles, editorials 1946 to present
CINAHL (EBSCOhost) Extensive coverage of nursing and allied health, including nursing and rehabilitation journals not covered by MEDLINE Journal articles, editorials, trade magazines 1937 to present
CENTRAL (Cochrane Library) CENTRAL is a sub-database (identified as Trials) in the Cochrane Library and contains records of randomized and quasi-randomized studies. The majority of the records come from MEDLINE and Embase but additional records from handsearching as well as those flagged in the Cochrane Review Groups' Specialized Registers are also included. Journal articles  
EMBASE (Ovid) European coverage in biomedicine, rehabilitation, pharmacology Journal articles, editorials, conferences 1947 to present
PsycINFO (Ovid) Excellent resource for research on psychological, social, behavioural and mental health questions Journal articles, books, book chapters, & dissertations 1806 to present
Scopus Multidisciplinary; "largest database" of peer-reviewed article records covering the arts, medicine, science, social sciences, and technology Journal articles, books, conference proceedings 1823 to present
Web of Science Core Collection Multidisciplinary; McGill coverage includes the Science Citation Index Expanded 1900- (SCI-EXPANDED), Social Sciences Citation Index 1956- (SSCI), Arts & Humanities Citation Index 1975- (A&HCI), Conference Proceedings Citation Index-Science  1900-(CPCI-S), Conference Proceedings Citation Index-Social Science & Humanities 1900- (CPCI-SSH), and the Emerging Sources Citation Index 2015- (ESCI) Journal articles, conference proceedings 1900 to present

Additional databases

Additional databases

If your question spans multiple disciplines and you would like more information on databases outside of this list, we suggest consulting the subject guides (also known as LibGuides) produced by McGill librarians.

Other high-quality knowledge syntheses published in the area of your research question can also be used for guidance.

Preliminary/exploratory searches in databases you are considering including can also give you a sense of how useful the database will be.

Developing and running the database searches

Developing and running the database searches

We recommend developing the search strategy in one database before translating the search strategy to the other selected databases: This will make it easier to keep track of things. If you subsequently find terms in the other selected databases, you can then go back and add them to the searches that have already been developed.

It is recommended that you have your search strategy peer reviewed. For peer review criteria and critical appraisal search strategies, consult:

  • McGowan J, Sampson M, Salzwedel DM, Cogo E, Foerster V, Lefebvre C. PRESS Peer Review of Electronic Search Strategies: 2015 Guideline Statement. J Clin Epidemiol. 2016 Jul;75:40-6. doi: 10.1016/j.jclinepi.2016.01.021. Epub 2016 Mar 19. PubMed PMID: 27005575.

We also recommend running all the searches on the same day to make it easier to document the date in your manuscript. 

Once you have your searches developed and you are ready to run them, you can the export the records from each database to an EndNote library, which you will keep for your files.

Example of a worksheet

Worksheet for search terms

Keep track of the terms you will be using in your search strategy in whatever way works best for you. Below, we provide an example of a worksheet that can be used for this purpose. Depending on your research question, the list of terms can get quite long and can be difficult to manage if you are not recording them as you are finding them.

Subject headings - definition

Subject headings: Definition

A subject heading is an assigned word or phrase used in some databases to uniformly describe a concept. Searching using this standardized word or phrase, instead of keywords, means you do not need to worry about synonyms and spelling variations.

Example: The subject heading for cancer in MEDLINE (via PubMed) is the MeSH term Neoplasms. This means that all articles selected for indexing in MEDLINE that are about cancer at a general level will be tagged or indexed with this subject heading, or if the article is about a specfic cancer like breast cancer, with a narrower term (note: there is a time delay between the addition of records to MEDLINE and their indexing).

Tutorials on using subject headings

We recommend the following resources if you would like to explore subject headings in more detail:

Keywords - definition

Keywords: Definition

Keyword (or textword) searching is when we search for words which we expect to find in the title, abstract, or author-defined terms of relevant articles; it is how we typically interrogate web search engines. Draw up a list of words or phrases related to each concept in your research question. When using this technique, you will need to be aware of synonyms and spelling variations.

Example: Keywords (or textwords) for cancer can include cancer / cancers / cancerous / neoplasm / neoplasms / neoplastic / tumor / tumors / tumour / tumours etc.

All databases - Boolean operators

Boolean operators

AND

  • retrieves records that include all of your search terms
  • e.g., diet therapy AND bulimia

OR

  • retrieves records that contain at least one of your search terms
  • e.g., (dog OR canine)

NOT

  • retrieves records that contain your first term but exclude your second term
  • e.g., dementia NOT alzheimer's
  • we do not usually recommend that you use NOT in your searches, as you may exclude relevant results

Note: Capitalize your operators as a matter of practice. In some databases, it does not matter whether you enter them in uppercase or lowercase, but others (like PubMed or Google Scholar) require them to be in uppercase.

Boolean operators - Tutorial

Boolean operators can be placed between your search terms to narrow or broaden a search, or to exclude search terms.

You will find below a brief video on how to use the boolean operators:

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