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 https://training.cochrane.org/handbook/current/chapter-04#section-4-2-2
Systematic searching is:
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 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, such as Breast Neoplasms.
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:
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).
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:
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:
(That said, some databases include lemmatization.)
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.
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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. |
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.
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 (with caution) 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 (EBSCOhost), Embase (Ovid), Scopus, and Web of Science Core Collection. It does not translate 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: It may not translate search fields accurately, and may leave in extraneous data.
The University of South Australia has some handy PDF guides on search translation:
Run your search on other databases
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 as .ris files. These can be imported into citation software or into knowledge synthesis software such as Covidence.
These tutorials will help you explore subject headings, subheadings, keywords, and search strategy refinement in more detail.
Health Sciences Library, McMaster University. (2020, January 7). OVID Medline - Part 1 - Starting Your Search [Video file]. Retrieved from https://hslmcmaster.libguides.com/tutorials/ovid
Health Sciences Library, McMaster University. (2014, October 16). OVID Medline - Part 2 - Refining Your Search [Video file]. Retrieved from https://hslmcmaster.libguides.com/tutorials/ovid
Welch Medical Library, Johns Hopkins University. (2020 June 30). PubMed: Building a Search [Video File]. Retrieved from https://www.youtube.com/watch?v=xGYFDrORpzA
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