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:
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.
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.
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 by 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 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 specific cancer like breast cancer, with a narrower term.
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).
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
Health Sciences Library, McMaster University. (2020, January 7). CINAHL Part 1 - Starting Your Search [Video file]. Retrieved from https://www.youtube.com/watch?v=mLL76nwhYUY
Health Sciences Library, McMaster University. (2014, May 15). CINAHL Part 2 - Refining Your Search [Video file]. Retrieved from https://www.youtube.com/watch?v=0kszOLxyI6g&feature=youtu.be
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; it is how we typically interrogate web search engines like Google. 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.
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: Capitalize your operators as a matter of practice. In some platforms or search systems, it does not matter whether you enter them in uppercase or lowercase, but others (like Google Scholar) require them to be in uppercase to work properly.
Use parentheses to set the order of execution of the Boolean logic. Parentheses work in most but not all systems (e.g., they work on the Ovid, PubMed, EBSCOhost, ProQuest, Scopus, and Web of Science platforms, but they are ignored in Google and Google Scholar)
e.g., (chest OR thorax OR thoracic) AND (imaging OR radiographs OR radiography)