EPIB 629 Knowledge Synthesis

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:

• 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

Need help choosing which databases to search for a health sciences review? 

• Chapter four of the Cochrane Handbook states that it is mandatory to search CENTRAL, MEDLINE, and Embase (the latter when available to the review team, which is the case at McGill) for all Cochrane reviews (4.3.1.1). Other databases are also suggested in the technical supplement to chapter 4, particularly if you are performing region- or subject-specific searches covered in more specialized databases (e.g., CINAHL, PsycINFO, or regional databases).
• Bramer et al. (2017) recommend searching the following based on their analyses: Embase, Ovid MEDLINE ALL, Web of Science Core Collection, and the first 200 records in Google Scholar. Keep in mind that Web of Science Core Collection may include different indexes depending on the institutional subscription. 
• See the table below for other frequently searched databases in health sciences, or consult a health sciences librarian.

The Cochrane group also has a living list of resources you can consult.

This table lists some of the differences between the core databases used in health sciences.

• Global Index Medicus

If your question spans multiple disciplines and you would like more information on databases outside of this list, we suggest

• Consulting the library guides (also known as LibGuides) produced by McGill librarians to get a sense of resources available at McGill.
• Referring to other high-quality knowledge syntheses published in the area of your research question. Cross-reference the methods sections of well-conducted syntheses published in the field of your synthesis topic.
• Consulting topic experts for further guidance
• Conducting preliminary/exploratory searches in databases you are considering including, to give you a sense of how useful the database will be.
• Try the Search Smart database: Allows you to compare over 90 databases and their search systems. Note that not all databases are available at McGill. To quickly check most of our database subscriptions, see Databases A-Z.

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

• 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 as .ris files. These can be imported into citation software or into knowledge synthesis software such as Covidence.

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 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:

• 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).

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

Ovid MEDLINE

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 https://hslmcmaster.libguides.com/tutorials/ovid 

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 https://hslmcmaster.libguides.com/tutorials/ovid

PubMed

PubMed: Building a search

Welch Medical Library, Johns Hopkins University. (2020 June 30). PubMed: Building a Search [Video File]. Retrieved from https://www.youtube.com/watch?v=xGYFDrORpzA

Additional tutorials:

• PubMed Subject Search
• PubMed Subject Search: How It Works

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

Boolean operators

• Boolean operators work in many but not all databases, and not all operators may be available
• Some databases will have a different syntax to enter an operator, for example in Scopus, NOT is entered as AND NOT
• Refer to the database help files to find out if and how Boolean operators are supported

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.

OR

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

AND

• retrieves records that include all of your search terms
• e.g., ultrasound AND tuberculosis

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

Proximity operators

• Many bibliographic databases also allow use of proximity operators
• The operator, if available, is dependent on the database and platform being searched
• e.g., on the Ovid platform, adjn is used: primary adj3 care
• Please see the database-specific operators and search fields

Parentheses/brackets

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)

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:

Useful libary guides

Health Sciences LIterature Searching Basics

Systematic Reviews, Scoping Reviews, and Other Knowledge Syntheses

Librarian Involvement in Systematic Reviews, Scoping Reviews, and Other Knowledge Syntheses at McGill University