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EPIB-629: Knowledge Synthesis - Library Guide

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Has your review or synthesis already been done?

Has your review or synthesis already been done?

Finding systematic reviews or syntheses on your topic

Once you have a reasonably well defined research question, it is important to make sure your project has not already been recently and successfully undertaken. This means it’s important to find out if there are other research syntheses (including systematic reviews) that have been published or that are in the process of being published on your topic.

If you are submitting your systematic review for funding, for example, you may want to make a good case that your review or synthesis is needed and not duplicating work that has already been successfully and recently completed—or that is in the process of being completed. It is also important to note that what is considered “recent” will depend on your discipline and the topic.

Even if you do find another review or synthesis on your topic, it may be sufficiently out of date or you may find other defendable reasons to perform it again. In addition, looking at other research syntheses published around your topic may also help you refocus your question or redirect your research toward other gaps in the literature.

These tips may not cover every possible type of research synthesis but they provide a decent start.

To find other reviews or syntheses:

To find other reviews or syntheses:

Search databases specifically focused on systematic reviews using a very broad search strategy, databases such as:

The Cochrane Library (including systematic reviews of interventions, diagnostic studies, prognostic studies, and more) is an excellent place to start.

By default, the Cochrane Library will display “Cochrane Reviews” (Cochrane Database of Systematic Reviews, aka CDSR). You can ignore the results which show up in the Trials tab when looking for systematic reviews: They are records of controlled trials relevant to Cochrane reviews. There is also an option to see Other Reviews under "More".

The example shows the number of Cochrane Reviews with hiv AND circumcision in the title, abstract, or keywords.

In addition, you can perform a sufficiently developed search strategy on MEDLINE via PubMed (be as broad in your search as is reasonable) and then use the “Article types” filter for “Systematic Reviews” to see if other reviews have been published on your topic. Systematic reviews found in PubMed and not included in The Cochrane Library may require more careful critical appraisal for quality assessment.

See Systematic Reviews Search Strategy Applied in PubMed for details.

 

Alternative interface to PubMed: You can also search MEDLINE on the Ovid platform. Perform a sufficiently developed search strategy (be as broad in your search as is reasonable possible) and then apply the "limit" under Publication Types for Systematic Reviews (it is, in fact, a search filter, and not a publication checktag/limit; because it is not a checktag/limit, it is not as accurate).

The Systematic Reviews search strategy is based on the version used in PubMed.

From additional limits, under EBM-Evidence Based Medicine, choose Systematic ReviewOnce you have run your search, to limit to systematic reviews: Go to Additional Limits, and under EBM-Evidence Based Medicine, choose Systematic Review

Other approaches: To search for systematic reviews in Embase on Ovid, perform a reasonably developed search strategy (be as broad in your search as is reasonably possible) and then combine your search results with a systematic review filter developed for Embase on Ovid, e.g., filters available at https://sites.google.com/a/york.ac.uk/issg-search-filters-resource/filters-to-identify-systematic-reviews

Example of a filter used to find systematic reviews for BMJ Clinical Evidence (can be copied and pasted into the Embase search box then combined with the concepts of your research question):

(exp review/ or (literature adj3 review$).ti,ab. or exp meta analysis/ or exp "Systematic Review"/) and ((medline or medlars or embase or pubmed or cinahl or amed or psychlit or psyclit or psychinfo or psycinfo or scisearch or cochrane).ti,ab. or RETRACTED ARTICLE/) or (systematic$ adj2 (review$ or overview)).ti,ab. or (meta?anal$ or meta anal$ or meta-anal$ or metaanal$ or metanal$).ti,ab.

Additional, specialized databases you can search to find existing or in-process reviews

Systematic searching

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 attempt not bias 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

Core databases

Selecting databases to search

Need help choosing which database to search? This table shows you the differences between the core databases used in health sciences knowledge syntheses. 

Need help searching the databases? Start with this introduction to searching with subject headings and keywords.

Database (Platform) Subject coverage Publication types included Dates covered
MEDLINE (Ovid) / PubMed Primary biomedical database for health care research; we recommend searching MEDLINE on the Ovid platform (enhanced options for searching) or via PubMed (free platform) Journal articles, editorials 1946 to present
CINAHL (EBSCOhost) Extensive coverage of nursing and allied health, including nursing and rehabilitation journals not covered by MEDLINE Journal articles, editorials, trade magazines 1937 to present
CENTRAL (Cochrane Library) CENTRAL is a sub-database (identified as Trials) in the Cochrane Library and contains records of randomized and quasi-randomized studies. The majority of the records come from MEDLINE and Embase but additional records from handsearching as well as those flagged in the Cochrane Review Groups' Specialized Registers are also included. Journal articles  
EMBASE (Ovid) European coverage in biomedicine, rehabilitation, pharmacology Journal articles, editorials, conferences 1947 to present
PsycINFO (Ovid) Excellent resource for research on psychological, social, behavioural and mental health questions Journal articles, books, book chapters, & dissertations 1806 to present
Scopus Multidisciplinary; "largest database" of peer-reviewed article records covering the arts, medicine, science, social sciences, and technology Journal articles, books, conference proceedings 1823 to present
Web of Science Core Collection Multidisciplinary; McGill coverage includes the Science Citation Index Expanded 1900- (SCI-EXPANDED), Social Sciences Citation Index 1956- (SSCI), Arts & Humanities Citation Index 1975- (A&HCI), Conference Proceedings Citation Index-Science  1900-(CPCI-S), Conference Proceedings Citation Index-Social Science & Humanities 1900- (CPCI-SSH), and the Emerging Sources Citation Index 2015- (ESCI) Journal articles, conference proceedings 1900 to present

Additional databases

Additional databases

If your question spans multiple disciplines and you would like more information on databases outside of this list, we suggest consulting the subject guides (also known as LibGuides) produced by McGill librarians.

Other high-quality knowledge syntheses published in the area of your research question can also be used for guidance.

Developing and running the database searches

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.

Subject headings - definition

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 will be tagged or indexed with this subject heading or a subsidiary one (note: there is a time delay between the addition of records to MEDLINE and their indexing).

Tutorials

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

Keywords - definition

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.

Comparison table

Subject Headings (SH)

Keywords

Pre-defined "controlled vocabulary" terms

Natural language words 

Need to know the exact controlled vocabulary term

Need to think of all synonyms, spelling variations, etc.

Less flexible. Not always an appropriate SH available

Quick & flexible way to start exploratory searches

Database looks for subjects only in the subject heading or descriptor field

Database looks for keywords anywhere in the record

Highly relevant results

Generates irrelevant results

 

Database and platform cheat sheet

Database and platform cheat sheet: PubMed, Ovid Online, Web of Science

 

PubMed (MEDLINE)

 

Ovid Online

 

Web of Science
Command Search

Subject headings

 

MeSH (Medical Subject Headings)

 

MEDLINE: MeSH
Embase: EMTREE

Avoid cross-searching databases so that you can take advantage of the subject headings, if applicable

NA (includes Keywords Plus, searched by default)


TS=("mycobacterium tuberculosis")

Searching subject headings

"MeSH term"[mesh]


Includes narrower terms by default
"Tuberculosis"[mesh]

exp subject heading/


"Explode" to include narrower terms
exp tuberculosis/

NA

 

Searching major subject headings

"MeSH term"[majr]

Retrieves records in which the MeSH concept is considered a central topic of the article

"Tuberculosis"[majr]

exp *subject heading/

Retrieves records in which the subject heading is considered a central topic of the article

exp *tuberculosis/

 

Searching title/abstract

 

term[tiab]


tb[tiab]

Searches author keywords too

term.ti,ab


tb.ti,ab

Does not search author keywords in Ovid MEDLINE; to search author keywords too, use:

term.ti,ab,kf

tb.ti,ab,kf

 

Searching title terms

 

term[ti]


obesity[ti]

term.ti.


obesity.ti.

TI=(term)


TI=(obesity)

Searching title/abstract/
entry terms

term[tw]


infliximab[tw]

term.mp.


infliximab.mp.

TS=(term)


TS=(infliximab)

Phrase searching

 

terms in phrase[tw] OR "terms in phrase"[tw]

NB: Do NOT use quotations around truncated phrases in PubMed as PubMed will then ignore the truncation symbol; PubMed will phrase search by default when the search field is specified after the phrase (except [all fields])


participatory research[tw]

terms in phrase.mp. OR "terms in phrase".mp.


participatory research.mp.

"terms in phrase"
TS=("participatory

research")

Truncation

 

terms in phrase*[tw]


rheumatoid nodule*[tw]

terms in phrase*.mp. OR terms in phrase$.mp.


rheumatoid nodule*.mp.

"terms in phrase*"
TS=("rheumatoid

nodule*")

Adjacency searching

(to search for a term within x terms from another term)

NA; AND terms together instead (or phrase search)


(patient[tw] AND outcome*[tw])

termA adjn termB


patient adj2 outcome*.mp.

NEAR/x (by default,

NEAR = NEAR/15)
TS=(brown NEAR "spider bite")

All databases - Boolean operators

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

Boolean operators - Tutorial

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:

Search filters or hedges

What is a search filter?

Search filters, sometimes also called hedges, are search strategies that usually include a series of pre-elaborated free-text terms/textwords/words/phrases plus subject headings for a given concept, idea, or study design; these search strategies have already been developed to find literature on the concept/idea/study design of interest within a particular database/platform (e.g., for the MEDLINE database on the Ovid platform). They may or may not have been validated for their sensitivity/specificity/precision, but when available, they are a useful tool to take advantage of work that others have already done to identify terms to find literature on a given concept.

Useful sources of general search filters

Additional filters not listed above

In addition to using search filters or hedges, you may find it useful to consult other systematic reviews or knowledge syntheses related to at least one of the concepts of your search, to see how they developed the search strategy for the concept of interest. One trick, for example, is to search the Cochrane Library by restricting the term of interest to the title field in the record, and then looking at the search strategy in the full-text, as it is often well documented in Cochrane reviews. Ideally, you should check a few reviews given the quality of the searches can be quite heterogeneous.

 

RCT search filters for MEDLINE on Ovid, EMBASE on Ovid, and PubMed

Use these pre-formulated search strategies (database-specific) to increase the sensitivity of a search for randomized controlled trials. to do so, just copy and paste the appropriate strategy into the database search box:

RCT search filters/hedges

PubMed highly sensitive filter/hedge for RCTs, modified with addition of randomised[tiab]:

((randomized controlled trial[pt]) OR (controlled clinical trial[pt]) OR (randomized[tiab] OR randomised[tiab]) OR (placebo[tiab]) OR (drug therapy[sh]) OR (randomly[tiab]) OR (trial[tiab]) OR (groups[tiab])) NOT (animals[mh] NOT humans[mh])

Source:

Box 6.4.a, http://handbook-5-1.cochrane.org/

 

MEDLINE on Ovid highly sensitive filter/hedge for RCTs, modified with addition of randomised.ab.

((randomized controlled trial or controlled clinical trial).pt. or randomized.ab. or randomised.ab. or placebo.ab. or drug therapy.fs. or randomly.ab. or trial.ab. or groups.ab.) not (exp animals/ not humans.sh.)

Source:

Box 6.4.c, http://handbook-5-1.cochrane.org/

 

Embase on Ovid filter/hedge for controlled trials:

crossover-procedure/ or double-blind procedure/ or randomized controlled trial/ or single-blind procedure/ or (random* or factorial* or crossover* or cross over* or placebo* or (doubl* adj blind*) or (singl* adj blind*) or assign* or allocat* or volunteer*).tw.

Source:

6.3.2.2. What is in The Cochrane Central Register of Controlled Trials (CENTRAL) from EMBASE? http://handbook-5-1.cochrane.org/

(NB: does not remove animal studies as the MEDLINE version does)

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Exporting search results to EndNote

Exporting search results into EndNote

Note: This procedure helps you keep track of the information that will be needed to report the methods in the article and also to fill in the PRISMA flow diagram.

Have the right EndNote library open in the background before you begin exporting.

Note: We do not generally recommend using Safari as your browser during this process, although it can be used with some tweaking.

For more instructions on using EndNote or other software programs, please see the Citation Guide

The steps below cover Ovid MEDLINE, Embase Classic+Embase on Ovid, PubMed, and Web of Science.

Exporting from Ovid Online

Ovid MEDLINE

We often start by exporting records from Ovid MEDLINE, if applicable (you may have decided to only use PubMed to search MEDLINE; those instructions are below):

  1. In EndNote, create a new library for the records from the database in question (MEDLINE on Ovid) and have the library ready in the background
  2. From Ovid, export complete reference in groups of <= 1000 (e.g., 1-1000, 1001-2000), do this until all of your records are exported (Export > Export To: EndNote; Select Fields to Display: Complete Reference; Export Citations)

  1. Move batches of exported records to the library you created and check the final number of records in the library against the number of results listed in database
  2. From Ovid MEDLINE: Download the search history for your records: Export (1, 1-10) > choose Microsoft Word format, check off Search History, and save the Word document to your documentation folder, with a useful filename in a format like SearchTerms-yyyymmdd-MEDLINESearch-xRecords
    • Not including the records themselves, the search history can then be copied and pasted into an appendix of the article, to document the search strategy with exactness. Avoids transcription errors
  3. Save the search history to your personal Ovid account (free) and identify the search by database name and date; this greatly facilitates rerunning the search later if an update is needed
  4. Create a compressed version of the EndNote library for your records

Embase Classic+Embase

  1. In EndNote, create a new library for the records from the database in question (Embase Classic+Embase) and have the library ready in the background
  2. From Ovid, export complete reference in groups of <= 1000 (e.g., 1-1000, 1001-2000), do this until all of your records are exported (Export > Export To: EndNote; Select Fields to Display: Complete Reference; Export Citations)

  1. Move batches of exported records to the library you created and check the final number of records in the library against the number of results listed in database
  2. From Ovid Embase: Download the search history for your records: Export (1, 1-10) > choose “Microsoft Word” format, check off “Search History”, and save the Word document to your documentation folder, with a useful filename in a format like SearchTerms-yyyymmdd-EmbaseSearch-xRecords
    • Not including the records themselves, the search history can then be copied and pasted into an appendix of the article, to document the search strategy with exactness. Avoids transcription errors
  3. Save the search history to your personal Ovid account (free) and identify the search by database and date; this greatly facilitates rerunning the search later if an update is needed
  4. Create a compressed version of the EndNote library for your records

Exporting from PubMed

PubMed

  1. In EndNote, create a new library for the records from the database in question (PubMed) and have the library ready in the background
  2. From PubMed, Click on Send To > Choose Destination: File > Format: MEDLINE > Create File

  1. In Firefox: Open with EndNote

  1. If the file was saved to your computer instead of automatically being imported into EndNote, import the file into EndNote (In EndNote menu: File > Import > File and locate the saved PubMed file on your computer) > Select PubMed (NLM) filter (if not visible, click “Other Filters…” to find it)

 

  1. Save the search history for your records: From PubMed: Click Create alert under the search box or from the Advanced screen, click Download history to maintain the line-by-line version (if applicable). The search is saved in an agglomerated format but this is useful if you need to rerun the search later for an update
  2. Create a compressed version of the EndNote library for your records

Exporting from Web of Science

Web of Science

  1. In EndNote, create a new library for the records from the database in question (Web of Science) and have the library ready in the background
  2. In Web of Science, Click on the arrow for the Save to EndNote online dropdown menu and select Save to EndNote desktop
  3. Export full records in groups of up to 500 (e.g., 1-500, 501-612)
  4. Move batches of exported records to the library you created and check the final number of records in the library against the number of results listed in database
  5. From Web of Science: Copy and paste the search history into a Word document, adjust the formatting
  6. You can save the search history as a file on your computer and this file can later be uploaded to Web of Science to re-execute the search; this is useful later if an update is needed
  7. Create a compressed version of the EndNote library for your records

Creating a backup, compressed EndNote library for your records

Create a backup, compressed EndNote library for your records

  • Before merging the libraries, create compressed libraries of each of the EndNote libraries from the individual database searches: Keep these compressed libraries for your records
  • Using the uncompressed versions of those libraries, bring all the records from your separate searches in to one EndNote library if you haven’t done so already: From EndNote menu, File > Import > File > locate individual .enl files; Import: EndNote library. You will perform deduplication in this library.

Creating a new EndNote library for deduplication and backup after deduplicating

Create a new EndNote library for deduplication and backup after deduplicating

Removing duplicates

See the instructions on deduplicating in EndNote.

Create a compressed library for backup after having removed all duplicates, with a filename like SearchTerms-yyyymmdd-Deduplicated—xRecords.enlx. This will be the library for screening.

Deduplication Method

Create a new EndNote library for deduplication and backup after deduplicating

 
Removing duplicates

Create a compressed library for backup after having removed all duplicates, with a filename like SearchTerms-yyyymmdd-Deduplicated—xRecords.enlx. This will be the library for screening. You can export the deduplicated library to Rayyan, for example, or other synthesis software, to facilitate the screening process, which usually involves more than one reviewer.

 

Bramer et al. have published more detailed and developed instructions on how to remove duplicates from an EndNote library.

Important information to document

Important information to document for the search

Record the information in a separate document:

Information Example
Names of databases/platforms searched Ovid MEDLINE
Database time coverage 1946-Present
Date searched January 12, 2018
Number of records from each database before deduplicating

Ovid MEDLINE: 1023

Ovid Embase: 2046

Number of records after deduplicating 2056
Search strategy from each database

Ovid MEDLINE

1. Silicone gels/
2. Silicone elastomers/
3. Silicon*.tw.
4. (gels or gel).tw.
5. Cica care.tw.
6. Or/1–5
7. Cicatrix, hypertrophic/
8. (hypertrophic adj3 scar*).tw.
9. Hypertrophic cicatrices.tw.
10. Hypertrophic cicatrix.tw.
11. Or/7–10
12. 6 and 11

 

Finding full text

Finding full text

Here are the steps I usually take when tracking down full-text articles. 

First, I like to perform these steps with VPN running in the background if off campus, for Google in particular;

I use EndNote to collect my references (or other citation management software, if the option is available):

  • Given I have usually exported my records to EndNote, I use the Find Full Text feature in EndNote to automatically download as many full-text articles to my EndNote library as I can (usually in batches no greater than 20, but that's just a suggestion); they get added to the .Data folder but I don't usually access that folder as the article can be viewed and annotated directly from the EndNote reference
    • You can configure file naming conventions for your .Data PDF folder so that they're easier to identify, if you ever want to go in there and make a copy of a PDF, for example (otherwise, the PDFs are very hard to identify): Go to Preferences > PDF Handling and change the PDF Auto Renaming Options
  • Instructions on setting up Find Full Text

If that doesn't work:

  • I do a quick Google Scholar search http://scholar.google.ca for the article title and see if I can quickly get to full-text that way (I need to be using VPN for this to work well if off campus, or at least need to set up Google Scholar with “Find full text” links--works with or without a Google account: http://screencast.com/t/phPoO8BT3g); if that doesn’t work:
  • I copy and paste the journal title (rather than the article title) into the McGill WorldCat catalogue available at http://www.mcgill.ca/library (you can use quotations around the journal title for more precise results; best to use the full journal title over the abbreviated format) and check availability of the journal title through McGill (you can limit by format in the left-hand column to Journal/Magazine > then when you get the right journal record look at “view now” for e-access info followed by “availability” information if we don’t have it online); for e-access, you might have to click on a few URLs before getting to the right place; pay particular attention to the information about the time coverage available at McGill); if it’s not available online, it may be available in print:
  • Even if I don't get any results in the McGill WorldCat catalogue, I check the Classic Catalogue available at http://catalogue.mcgill.ca/F to make sure we really don't have the journal in print. To get articles that are available at McGill only in print, you can request a scanned copy of an article through the catalogue. The instructions can be found here: http://www.mcgill.ca/library/services/borrowing/students/scan-requests
  • If it’s seemingly not available at McGill:

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