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Systematic Review

This guide aims to provide tools and resources that can be used for conducting a systematic review in medical and health sciences.

Search Filters

The following list of search filters are designed and tested by search experts. You can apply them to limit your search to specific research designs or topics.

Sample Search Strategy

Here is a sample systematic review search strategy in Medline, Embase and Cochrane Library.

Yale MeSH Analyzer

Enter up to 20 PubMed unique identifiers (PMIDs) of publications that are relevant to your research topic. This allows you to analyze any patterns of assigned MeSH terms, i.e., which MeSH terms are more frequently used from the publications.

Developing a Search Strategy

Searching is a critical part of the systematic review. Before you start typing keywords into a database to run a search straightaway, it is crucial to plan your search strategy first. This process enables you to:

  • optimize the search that all (or most) potential studies relevant to your review question can be captured by the search strategy,
  • translate the search among databases easily,
  • run searches in an organised and reproducible way.

Steps to develop a search strategy:

  1. Translate your research question into question formation framework such as PICO framework.
  2. Identify the key concepts of your topic or key elements* from the PICO.
  3. Think of all possible synonyms, variations and related terms for each concept or the PICO elements.
  4. Apply search techniques such as boolean operators, nesting, phrase searching, truncation and wildcards.
  5. Consider if certain keywords have to be searched in particular search fields such as Title & Abstract.
  6. Identify relevant subject headings (e.g. MeSH for Medline, Emtree for Embase, etc) and add them to your search.
  7. Apply search filters or limits to narrow the search (e.g. date/year of publication, age, gender, article type, or language of publication).
  8. Run the search and evaluate the initial search results. Amend the search strategy as required.
  9. Translate the search strategy to other databases relevant to your research topics i.e., translate all subject headings and search operators, map search fields for keyword search, etc.).

* Not all elements of a research question or from the PICO should necessarily be used in the search strategy. Some elements are less important than others. Adding an element to a search strategy increases the chance of missing relevant search results. 

Tips:

  • Check the search strategies used in other systematic reviews most relevant to your review question for hints on keywords, search terms, subject headings and combinations to use.
  • Searching is an iterative process. It is necessary to amend the search strategy in order to conduct a thorough search for relevant studies.
  • Document the search process in a text document 

Suggested Databases to Search

Depending on your review question, you need to identify relevant databases to search in your review. The goal is to ensure your search is comprehensive.

Below are some of the key databases in Medicine and Health Sciences. Click here for the full list of databases.

  • MEDLINE via OvidSP  (with Medical Subject Headings)
    Coverage: 1946 - present
    ► US National Library of Medicine's bibliographic database of citations and abstracts currently from approximately 5,000 biomedical journals in the fields of medicine, nursing, dentistry, veterinary medicine, health care systems, and preclinical sciences. Coverage extends back to 1946 in which OLDMEDLINE records are included.
  • EMBASE (with EMTREE Subject Headings​)
    Coverage: 1910 - present
    ► EMBASE is a biomedical and pharmacological database containing bibliographic records with citations, abstracts and indexing derived from biomedical articles in peer reviewed journals, and is especially strong in its coverage of drug and pharmaceutical research.
  • CINAHL Ultimate (with CINAHL Subject Headings)
    ► CINAHL Ultimate provides nursing and allied health professionals access to leading nursing and allied health journals. It covers more than 50 nursing specialties and includes quick lessons, evidence-based care sheets, and research instruments.
  • Cochrane Library (with Medical Subject Headings)
    Coverage: 1996 - present
    ► The Cochrane Library is a collection of databases that contain high-quality, independent evidence to inform healthcare decision-making. These databases are: Cochrane Database of Systematic Reviews (CDSR), The Cochrane Central Register of Controlled Trials (CENTRAL), and Cochrane Clinical Answers (CCAs).
  • APA PsycInfo (with APA Thesaurus terms)
    Coverage: 1806 - present
    ► Provides abstracts and citations to the scholarly literature in the psychological, social, behavioral, and health sciences.
  • Web of Science (keyword search) 
    ► Multidisciplinary citation database. Web of Science Core Collection covers 20,000+ journals, including 8,850+ from Science Citation Index Expanded (SCIE), 3,200+ from Social Science Citation Index (SSCI) and 1,700+ from Arts & Humanities Citation Index (AHCI).

Medical Database Guides

Refer to the Medical Database Guides for information on searching Medline (Ovid), PubMed, EMBASE (Ovid), CINAHL Ultimate (EBSCOhost), and Cochrane Library.


Grey Literature to Search

What is Grey Literature?

Grey literature refers to materials and documents not controlled by commercial publishers and it is usually not discoverable in databases, making it difficult to search for and retrieve. Grey literature is produced by the government, academia and industry.

Grey Literature is also defined as:

"Information produced on all levels of government, academia, business and industry in electronic and print formats not controlled by commercial publishing i.e. where publishing is not the primary activity of the producing body."  Source: ICGL Luxembourg definition, 1997, Expanded in New York, 2004

Searches for studies should be as extensive as possible in order to reduce the risk of publication bias. It is highly desirable to search relevant grey literature sources such as reports, dissertations, theses, databases and conference abstracts/papers. (Source: MECIR Manual C28)

Examples of grey literature include:

  • theses and dissertations
  • trade publications, conference papers and conference proceedings
  • fact sheets, pamphlets, bulletins and newsletters
  • government documents, government reports, parliamentary proceedings, bills, issues papers, discussion papers and policy papers
  • practice guidelines and standards
  • interviews, surveys and speeches
  • informal communications e.g. emails and memorandums
  • online materials e.g. websites, webinars, podcasts, videos, tweets, blogs
  • market reports, annual reports and working papers.

Source: Grey literature - Tip Sheet from Queensland University of Technology Library

More examples of grey literature: GreyNet International - Document types in Grey Literature

Key sources for Theses and Dissertations:

Click here for more databases on Dissertations and Theses.

Key sources for Conference Abstracts & Proceedings:

Some library databases also include conference papers:

Search Tips: To limit search results to conference papers, look for the filters or limits on “Publication Type”, “Content Type”, or “Article Type” and select "meeting/conference abstracts", "proceedings paper", or "conference papers".

Many clinical trials are in progress, grey or unpublished. It's important to include searching unpublished and ongoing studies in your SR to minimise bias.

Source: Cochrane Handbook, 4.3.3

Key sources for Trials Registers:

  • ClinicalTrials.gov - is a database provided by the U.S. National Library of Medicine for searching privately and publicly funded clinical studies conducted around the world.
  • CENTRAL (Cochrane Central Registrar of controlled Trials) - contains randomized controlled trial (RCT) and quasi-RCT (q-RCT) records. Most CENTRAL records are taken from PubMed/MEDLINE and Embase, but records are also derived from other published and unpublished sources, including CINAHL, ClinicalTrials.gov and WHO ICTRP.
  • ISRCTN (International Standard Randomised Controlled Trial Number) Registry - is a numeric system for the unique identification of randomised controlled trials worldwide.
  • WHO ICTRP (WHO's International Clinical Trials Registry Platform) - provides a single point of access to ongoing and completed clinical trials. Trial records are harvested from key clinical trial registries, including but not limited to: ANZCTR (Australian New Zealand Clinical Trials Registry), ClinicalTrials.gov, EU Clinical Trials Register, and ISRCTN (International Standard Randomised Controlled Trial Number).

According to Cochrane Handbook, 4.3.3, "Research has shown that even though ClinicalTrials.gov is included in the WHO ICTRP Search Portal, not all ClinicalTrials.gov records could be successfully retrieved via searches of the ICTRP Search Portal." Therefore, you may also want to search individual trial registers.

  • Grey Matters: a practical search tool for evidence-based medicine - a free online resource for searching health-related grey literature provided by The Canadian Agency for Drugs and Technologies in Health (CADTH).
  • Mednar - a deep web search engine for retrieving medical information in real time.
  • OpenGrey - provides open access to 700.000 bibliographical references of grey literature (paper) produced in Europe covering Science, Technology, Biomedical Science, Economics, Social Science and Humanities.
  • The Grey Literature Report - the report is a publication produced by the The New York Academy of Medicine between 1999 - 2016, alerting readers to grey literature publications in health services research and selected urban health topics (content update ceased from 2017).
  • Institutional Repository for Information Sharing (WHO Library IRIS) - provides access to to reports, statistics, guidelines and regulations on global health matters from WHO as well as from other sources of scientific literature produced around the world.