Skip to Main Content

EPIB 619 Systematic Reviews & Meta-Analyses

What is a systematic search?

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 (...)

Lefebvre C, Glanville J, Briscoe S, Littlewood A, Marshall C, Metzendorf M-I, Noel-Storr A, Rader T, Shokraneh F, Thomas J, Wieland LS. Chapter 4: Searching for and selecting studies. In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.1 (updated September 2020). Cochrane, 2020. Available from

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

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 are assigned descriptors, similar to hashtags but from a controlled vocabulary, used in some databases to uniformly capture a concept. Searching using these standardized words or phrases, instead of text words, means you do not need to worry as much about synonyms and spelling variations, and also allows you to retrieve more precise results. In MEDLINE, the subject headings are MeSH terms, in Embase, they are EMTREE terms: It is important to keep in mind that the subject headings will in most cases be database-dependent.

Keep in mind that there may be a time delay between the addition of records to databases like MEDLINE and their indexing with subject headings like MeSH terms -- and in some databases, e.g., MEDLINE, some records will never be indexed, even when subject headings are available.

Example: The subject heading for cancer in MEDLINE (via PubMed) is the MeSH term Neoplasms. This means that 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 specific cancer like breast cancer, with a narrower term.

Example: This 1995 article record that is clearly about neoplasms does not contain any MeSH terms capturing that concept given the journal is only indexed (with MeSH terms) in MEDLINE as of volume 12 and this article appears in volume 6.

How you actually use subject headings in a database search (if they're even available) depends on the platform you're searching, e.g., to use the subject heading for 'Neoplasms' in PubMed or Ovid MEDLINE, which can both essentially be used to search MEDLINE:

  • PubMed: The search syntax is "Neoplasms"[Mesh] (You can also enter "Neoplasms"[mh] for the same effect; the safest way to use subject headings is to find them first in the MeSH Database, then to add them to the PubMed Search Builder, and then to Search PubMed). They will then be available in PubMed from Advanced > History and Search Details, and can then be combined with other search lines.
  • Ovid MEDLINE: The search syntax is exp neoplasms/ (The Advanced Search in Ovid MEDLINE at McGill is set up by default to "Map term to subject heading", so if you type in 'cancer', you will get a list of suggested subject headings, with 'Neoplasms' at the top; PubMed does not work that way). 

For thorough searches, you would generally include subject headings and their text word equivalents, plus any alternative terms (related terms, broader terms if needed, specific terms, synonyms, alternative spellings or variants, abbreviations).

Using keywords

Librarians in the health sciences often use subject headings as the foundation of search strategies. However, there are various reasons why we add keywords to a search:

  • For an emerging research topic which may not yet have a subject heading to describe it
  • To retrieve the most recent articles (which have not yet been indexed with subject headings)
  • Occasionally, articles can be incorrectly indexed (e.g., not assigned a relevant subject heading) and may be missed by a search using only subject headings
  • To develop a thorough search strategy for a systematic review or other knowledge synthesis, we always supplement the search with keywords

Keyword (or textword, natural language, or free-text) searching is when we, for example, search for words which we expect to find in the title, abstract, or author-assigned keywords of relevant articles (remember, most article databases do NOT search full text). Draw up a list of words or phrases related to each key concept in your research question. When using this technique, you will need to be aware of synonyms and spelling variations.

You should keep in mind that keywords do not generally account for:

  • Spelling variations
  • Synonyms
  • Plural forms

(That said, some databases include lemmatization.)

Truncation and wildcards for keywords

Truncation symbols are shortcut characters which can help to include variations of your text word without having to type each variation into the search separately. This feature is also known as stemming. The asterisk is the most common truncation symbol.

Depending on the platform you are using to search a given database (e.g., EBSCOhost, Ovid, ProQuest), other truncation and wildcard symbols may be available to use, for example, within words. Please see the database-specific operators and fields for more information.



Depending on the database or platform, use before (uncommon feature, available in Web of Science and Scopus, for example), within (as a wildcard, depends on database/platform), or at the end of a word root or string (most common option) to replace zero to multiple characters. For more information, please see the search tips (below or within the database/platform help files) on wildcard/truncation options available in commonly used databases or platforms in health sciences

e.g. computer* retrieves computer, computers, computerised, computerized, etc.

Keywords - examples

Example: Keywords (or textwords) for cancer can include cancer / cancers / cancerous / malignancies / malignancy / malignant / metastasis / metastases / metastatic / neoplasia / neoplasm / neoplasms / neoplastic / tumor / tumors / tumour / tumours etc.

  • Note that cancer is a very broad concept that refers to many specific types of cancer as well, such as astrocytomas / carcinoma / chordoma / craniopharyngioma / ependymoma / esthesioneuroblastoma /  glioblastoma / glioma / leukemia / leukaemia / lymphoma / medulloblastoma / melanoma / mesothelioma / myeloma / myelodysplastic syndromes / myeloproliferative disorders / osteosarcoma / retinoblastoma / rhabdomyosarcoma / sarcoma / thymoma etc.
  • To search for a combination of textwords, combine synonyms with OR with the use of truncation/wildcards when applicable, e.g., in Ovid databases: (cancer* OR malignan* OR metasta* OR neoplas* OR tumo?r* OR astrocytoma* OR carcinoma* OR chordoma* OR craniopharyngioma* OR ependymoma* OR esthesioneuroblastoma* OR glioblastoma* OR glioma* OR leuk?emi* OR lymphom* OR medulloblastoma* OR melanom* OR mesothelioma* OR myeloma* OR myelodysplasi* OR myeloproliferative OR osteosarcoma* OR retinoblastoma* OR rhabdomyosarcoma* OR sarcoma* OR thymoma*).mp. etc.
    • Note that the asterisk is a fairly universal symbol for truncation, but other wildcards (e.g., replacing 0 or 1 character with ? in Ovid) will differ depending on the platform used (e.g., Ovid versus EBSCOhost versus Scopus versus Web of Science)
    • The search syntax for searching for textwords will also differ depending on the platform (e.g., (terms).mp. in Ovid can be translated as TS=(terms) in Web of Science)
  • Such a list of terms for a broad concept like cancer is far from exhaustive: Consider narrowing the focus of your question to a particular type of cancer, for example, when possible, or justifying use of broader terms only

Translating and running searches

We recommend developing the search strategy in a primary 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 search(es) that has (have) already been developed as well as integrate them into the remaining searches.

You can use a tool called SRA Polyglot to help with the search translation from MEDLINE on Ovid or from PubMed to a number of databases, such as CENTRAL (Cochrane Library/Wiley), CINAHL (EBSCO), Embase (Ovid), Scopus, and Web of Science Core Collection. It does not correct the subject headings, however, and you will need to do that manually (identifying the applicable subject headings in CINAHL and Embase, for example, then updating the searches accordingly, and removing them from databases in which they may have become redundant or nonsensical, e.g., when words are inverted). We also caution that using it properly requires more advanced database searching skills.

The University of South Australia has some handy PDF guides on search translation:

Run your search on other databases - instructions for translating a search to Scopus, Web of Science, CINAHL, SPORTDiscus (EBSCOhost), Cochrane Library, ERIC (ProQuest), and ProQuest Dissertations and Theses Global

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 then export the records from each database to an EndNote library or export the records as .ris files. These can be imported into citation software or into knowledge synthesis software such as Covidence.

Tutorials on searching

These tutorials will help you explore subject headings, subheadings, keywords, and search strategy refinement in more detail.


Ovid MEDLINE part 1 - Starting your search (using subject headings)

Health Sciences Library, McMaster University. (2020, January 7). OVID Medline - Part 1 - Starting Your Search [Video file]. Retrieved from 

OVID Medline - Part 2 - Refining your search (using keywords, operators, and limits)

Health Sciences Library, McMaster University. (2014, October 16). OVID Medline - Part 2 - Refining Your Search [Video file]. Retrieved from


PubMed: Building a search

Welch Medical Library, Johns Hopkins University. (2020 June 30). PubMed: Building a Search [Video File]. Retrieved from

Additional tutorials:


CINAHL Part 1: Starting your search

Health Sciences Library, McMaster University. (2020, January 7). CINAHL Part 1 - Starting Your Search [Video file]. Retrieved from

CINAHL Part 2 - Refining your search

Health Sciences Library, McMaster University. (2014, May 15). CINAHL Part 2 - Refining Your Search [Video file]. Retrieved from

Liaison Librarian

Profile Photo
Genevieve Gore
Liaison Librarian, Schulich Library of Physical Sciences, Life Sciences, and Engineering
Contact: Website

Need help? Ask us!

McGill LibraryQuestions? Ask us!
Privacy notice