EPIB 619 Systematic Reviews & Meta-Analyses

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

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.

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

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 with MeSH terms, and some records will not be indexed at all).

How the subject headings are actually used in a database (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:

• 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)
• 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)

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

PubMed tutorials:

Using MeSH in Pubmed  (3 min 02)

• What is MeSH?

CINAHL (on EBSCOhost) tutorial:

Using Subject Headings in CINAHL (3 min 32)

Ovid MEDLINE tutorials:

Advanced Search on the Ovid Platform (with a focus on Ovid MEDLINE, using MeSH subject headings as well as subheadings) (13 min 25)

See also:

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

Health Sciences Library, McMaster University. (2014, October 16). OVID Medline - Part 1 - Starting Your Search [Video file]. Retrieved from https://www.youtube.com/watch?v=Qm2tuuxqftg#action=share

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://www.youtube.com/watch?v=wtO-KdQRtUg&feature=youtu.be

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.

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

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 searching tips listed by database

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.

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)

Useful libary guides

Health Sciences Research Basics

Systematic Reviews, Scoping Reviews, and Other Knowledge Syntheses

Systematic Review Service

Rayyan for Screening Records in Systematic Reviews