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Systematic Reviews

Conduct literature searches

Step 3: Conduct comprehensive literature searches on your research question to find all the evidence. This is where the librarian is most involved:

  1. Work with a UAB librarian experienced in conducting comprehensive literature searches.
  2. Submit an official request through the Expert/Systematic Review Search Request Form.
  3. Define the main concepts of your topic.
  4. List terms to describe each concept.
  5. A librarian can give advice on which databases should be included in the search (three minimum).
  6. A librarian will create a search strategy and use the included standards/techniques:
    1. Format concepts with the correct Boolean operators.
    2. Use database-specific syntax and subject headings with appropriate use of explosion, subheadings, and floating subheadings, when necessary.
    3. Use of appropriate natural language (keywords), synonyms, acronyms, etc. with appropriate field tags.
    4. Use truncation and spelling variations as appropriate.
    5. Appropriate use of limits and filters.
    6. Check indexing of exemplar articles.
  7. A librarian will translate the search strategy to match the format standards for each database.
  8. Consider the inclusion of grey literature sources - see below for more information. 
  9. Librarian will save a copy of your search strategy and details about your search.

Standards for reporting & documenting your search

PRISMA-S Literature Search Extension is a standard for clear and concise reporting of your search methodology. It is a 16-item checklist that covers multiple aspects of the search process for systematic reviews. It is intended to guide reporting, not conduct, of the search. The checklist should be read in conjunction with the Explanation and Elaboration (Part 3), which provides more detail about each item.

 

Rethlefsen ML, Kirtley S, Waffenschmidt S, Ayala AP, Moher D, Page MJ, Koffel JB; PRISMA-S Group. PRISMA-S: an extension to the PRISMA Statement for Reporting Literature Searches in Systematic Reviews. Syst Rev. 2021 Jan 26;10(1):39. doi: 10.1186/s13643-020-01542-z. PMID: 33499930; PMCID: PMC7839230.

  • Review authors should work closely, from the start of the protocol, with an experienced medical librarian.
  • Searches should aim for high sensitivity, which may result in relatively low precision.
  • Search strategies should avoid using too many different search concepts but a wide variety of search terms should be combined with OR within each included concept.
  • Both free-text and subject headings (e.g. Medical Subject Headings (MeSH) and Emtree) should be used.

 

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 6.2 (updated February 2021). 

  • 3.1.1 Work with a librarian trained in performing systematic reviews (SRs) to plan the search strategy
  • 3.1.2 Design the search strategy to address each key research question
  • 3.1.3 [summarized] independent peer review of search
  • 3.1.4, 3.15 Search bibliographic databases + indexes
  • 3.1.6 Search literature cited by eligible studies
  • 3.1.7 Update the search at intervals appropriate to the pace of generation of new information for the research question being addressed

Institute of Medicine 2011. Finding What Works in Health Care: Standards for Systematic Reviews. Washington, DC: The National Academies Press. https://doi.org/10.17226/13059.

How a Librarian can help with searching the literature

In step 3, partner with a librarian early on in the process:

The goal of a systematic retrieve is to find all results that are relevant to your topic. Because systematic review searches are quite extensive and retrieve large numbers of results, an important aspect of systematic searching is creating a high quality search and limiting the number of irrelevant results that need to be screened. In addition to having a high quality search, the searches should be well-documented and reproducible. Click through the tabs below to review core tenets and guidance from both the Cochrane Handbook for Systematic Reviews, the National Academies Press / IOM and the PRISMA-S Extension.

Librarians are experts trained in literature searching and systematic review methodology. Partner with the Systematic Review Librarians at UAB to save time and improve the quality of your review. Our Librarian Expertise page details how our librarians collaborate with and contribute to systematic review teams.

UAB Libraries Databases

Based on the Bramer Search Method, librarians are advised to use a combination of at least three databases for optimal retrieval of studies. Regardless of the systematic review's topic, "a combination of Embase, Ovid MEDLINE, Web of Science Core Collection, & Google Scholar (only the first 200 relevant citations) performed best, achieving an overall recall of 98.3 and 100% recall in 72% of systematic reviews" (Bramer, 2017). 

The Core Major Biomedical Databases from UAB Libraries that should be considered for inclusion in health-related Systematic Review searches:

 

To learn how to conduct searches in health sciences databases, watch this short tutorial:

Many systematic review topics benefit from using subject-specific databases that offer robust coverage and unique citations within their respective fields. These specialized resources ensure a more comprehensive and relevant evidence base for your review:

 

To explore our full range of databases, visit our Databases page. A librarian is also available to help you identify the most appropriate databases for your research topic or discipline.

Grey Literature: Definition and How to Search

"Grey literature stands for manifold document types produced on all levels of government, academics, business and industry in print and electronic formats that are protected by intellectual property rights, of sufficient quality to be collected and preserved by libraries and institutional repositories, but not controlled by commercial publishers; i.e. where publishing is not the primary activity of the producing body."

- The Twelfth International Conference on Grey Literature in Prague in 2010. 

Examples of grey literature include: conference abstracts, presentations, proceedings; regulatory data; unpublished trial data; government publications; reports (such as white papers, working papers, internal documentation); dissertations/theses; patents;  and policies & procedures.

Inclusion of grey literature into a systematic review is recommended in order to help minimize publication bias. The inclusion of grey literature in systematic reviews is widely recognized as important and international organizations have incorporated this information in their guidelines and manuals for working on reviews and meta-analyses.

  • AHRQ: Finding Grey Literature Evidence and Assessing for Outcome and Analysis Reporting Biases When Comparing Medical Interventions
    This is a chapter from AHRQ's "Methods Guide for Effectiveness and Comparative Effectiveness Reviews."
  • Cochrane Handbook: Unpublished and Onging Studies
    From the Cochrane Handbook for Systematic Reviews of Interventions. Version 5.1.0 [updated March 2011]
  • Cochrane Handbook: Including unpublished studies in systematic reviews
    From the Cochrane Handbook for Systematic Reviews of Interventions. Version 5.1.0 [updated March 2011]
  • The Joanna Briggs Institute Reviewer's Manual
    Aromataris E, Munn Z (Editors). Joanna Briggs Institute Reviewer's Manual. The Joanna Briggs Institute, 2017. Available from https://reviewersmanual.joannabriggs.org/
  • PRISMA for systematic review protocols (PRISMA-P)
    Item 9: "Describe all intended information sources (such as electronic databases, contact with study authors, trial registers or other grey literature sources) with planned dates of coverage."

Searching the grey literature can be a daunting task. You should search those resources that make the most sense for your research question. At a minimum, consider searching unpublished trial data through trial registries as well as conference abstracts. Also check out the papers and reports of relevant stakeholder organizations.

The links below may shed some additional light on the process.

Sources of Grey Literature

Online clinical trial registries can be valuable sources for identifying completed but unpublished clinical trials. These resources often provide otherwise inaccessible information, including additional details about published studies. While some registries include study results, even the identification of a trial—regardless of result availability—can be useful, as reviewers may contact the principal investigator directly for further information. Many pharmaceutical companies also host trial registries on their own websites, though the quality and completeness of these vary.

 
Additional resources to consider:
  • CenterWatch: Profiles over 875 clinical research centers and 600 companies. It provides tools to locate research centers by medical expertise or region, as well as to identify industry providers by the type of services offered.
  • ClinicalResearch.com: Offers trial listings and information for both participants and researchers.
These resources can help identify ongoing, completed, or unpublished research projects relevant to systematic reviews. They are particularly useful for locating grey literature and minimizing publication bias:
 
  • NIH RePORTER: A searchable database of NIH-funded research projects. Includes links to resulting publications and patents. Useful for identifying funded but unpublished or ongoing studies.
  • HSRProj (Health Services Research Projects in Progress): Maintained by the National Library of Medicine, this database provides detailed information on ongoing health services research and public health projects in the U.S.
  • AHRQ Grants On-Line Database: A searchable database of Agency for Healthcare Research and Quality–funded research grants. Allows filtering by program area, priority populations, and Recovery Act projects.
  • HSRR (Health Services and Sciences Research Resources): Provides descriptions of datasets, instruments, and software tools used in health services research, behavioral and social sciences, and public health. Includes links to relevant PubMed records when available.
  • NTIS (National Technical Information Service): A repository of U.S. government-funded scientific, technical, engineering, and business-related research reports. Useful for accessing older or obscure government publications and grey literature.

These organizations and repositories offer access to international research outputs, systematic reviews, and grey literature. They can be valuable for identifying health interventions, public health studies, and region-specific evidence not indexed in traditional databases.

  • Centre for Reviews and Dissemination (UK): Based at the University of York, CRD conducts and supports systematic reviews and maintains key databases including DARE, NHS EED, and HTA, which provide high-quality evidence on health and social care interventions.

  • INAHTA (International Network of Agencies for Health Technology Assessment): A non-profit network of 50+ member agencies from around the world. Focuses on sharing evidence-based assessments to inform health policy and decision-making.

  • INIST (Institut de l’Information Scientifique et Technique): Part of the French National Center for Scientific Research (CNRS), INIST develops tools and services to enhance access to international scientific and technical information, especially from basic and applied research.

  • WHO International Clinical Trials Registry Platform (ICTRP): Aggregates clinical trial data from registries worldwide to ensure transparency and accessibility of global clinical research.

  • Lenus (Irish Health Repository): Managed by the Health Service Executive (HSE) Library, Lenus provides open access to Irish health research, including theses, reports, and evaluations.

  • NARCIS (Netherlands): Formerly the national portal for Dutch research information, NARCIS provided access to publications, datasets, and researcher profiles (note: now integrated into the Dutch Research Portal via NWO/DTL).

  • RIAN (Ireland): The national open access research portal for Ireland. Aggregates research from Irish institutional repositories, including dissertations, articles, and technical reports.

  • UK Clinical Research Network (UKCRN) Study Portfolio: A searchable portfolio of studies supported by the NIHR Clinical Research Network. Includes studies from England, Wales, Scotland, and Northern Ireland.

  • Virtual Health Library (VHL/BVS): Coordinated by the Pan American Health Organization, the VHL provides access to Latin American and Caribbean health science literature and grey literature across multiple regional databases (e.g., LILACS).

  • WHO Publications: The World Health Organization’s official platform for reports, guidelines, technical documents, and global health research outputs.

Many pharmaceutical companies maintain registries or databases of their sponsored clinical trials. While the level of transparency and data availability varies, these sites can provide results for completed studies that may not be published in peer-reviewed journals. They are valuable for identifying unpublished or supplemental trial data relevant to systematic reviews.

 

 

Note: Transparency and usability of pharmaceutical company trial registries can vary. Researchers are encouraged to verify data availability and consult ClinicalTrials.gov or the EU Clinical Trials Register for broader context or supplementary information.

The drug and device approval process often requires submission of detailed clinical data that may not be available through traditional publication channels. These regulatory sources can help reviewers identify potential publication bias and gather supplementary trial data. While some documents may be redacted or only available post-approval, they offer valuable insight into both published and unpublished research.

Primary Sources:

  • Drugs@FDA: Hosted by the U.S. Food and Drug Administration, this database can be searched by drug name or active ingredient. Within each drug’s page, select “Approval History, Letters, Reviews, and Related Documents” to access internal FDA reviews, which often summarize clinical trial data submitted during the approval process.

  • Devices@FDA: Includes approval documents and summaries for medical devices cleared by the FDA from 1995 onward. Documents often include clinical trial results, safety summaries, and effectiveness data.

  • Health Canada Drug Product Database (DPD): A comprehensive source for drugs approved in Canada. Some entries include links to drug monographs, which may summarize trial data or reference supporting clinical studies.

  • European Public Assessment Reports (EPARs): Published by the European Medicines Agency (EMA), EPARs provide detailed scientific assessments for all centrally authorized medicines in the EU. These reports typically include summaries of pre-approval clinical trial data.

Additional Resources:

  • FDA Dockets Management: The FDA’s public docket system for administrative proceedings and rulemaking. It includes documents such as hearing transcripts, public comments, and presentation materials. Occasionally, these contain unpublished trial data discussed in regulatory settings.

  • FDA MedWatch: The FDA’s safety reporting system, providing safety alerts, labeling changes, and voluntary reporting tools for adverse events related to medical products.

  • Drug Information Portal: Managed by the National Library of Medicine, this portal aggregates information on drugs from multiple sources, including the FDA, CDC, and NIH. Useful for quickly locating regulatory and research context for a specific drug.

These tools and repositories can help identify non-commercial, non-peer-reviewed, or hard-to-find literature such as reports, theses, preprints, protocols, and institutional research. They are essential for reducing publication bias and ensuring comprehensive systematic reviews.

  • Google Scholar: A freely accessible web search engine that indexes scholarly literature across disciplines. It includes journal articles, theses, books, abstracts, and court opinions. Note: Coverage is broad but not transparent, and search algorithms are proprietary.

  • Grey Literature Report (Archived): Formerly maintained by the New York Academy of Medicine, this quarterly publication indexed public health grey literature. Though no longer updated after 2016, past reports remain useful for historical context.

  • Joanna Briggs Institute (JBI): An international organization based at the University of Adelaide that produces systematic reviews and other forms of evidence syntheses focused on feasibility, appropriateness, and clinical effectiveness in healthcare. JBI reviews are often included in Ovid and JBI’s own EBP Database.

  • OAIster: A union catalog of millions of records from open access repositories, managed by OCLC. Useful for locating grey literature, dissertations, and institutional reports.

  • OpenDOAR (Directory of Open Access Repositories): A global directory of academic open access repositories, searchable by country, institution, or subject. Helps identify sources for unpublished or institutionally archived research outputs.

  • PROSPERO (International Prospective Register of Systematic Reviews): A global registry for systematic reviews in health and social care. Records review protocols at inception, helping promote transparency and reduce duplication. Also enables comparison between planned and reported methods/results.

  • Registry of Open Access Repositories (ROAR): An international registry that indexes open access repositories to support the growth of open scholarly communication.

  • Sigma Repository (formerly Virginia Henderson Global Nursing e-Repository): An open-access platform hosted by Sigma Theta Tau International, dedicated to sharing nursing-focused research, education materials, and evidence-based practice projects. Especially useful for identifying grey literature in nursing.

Credits

This page was based on pages from the University of North Carolina Health Sciences Library and Duke University Medical Center Library & Archives guides on screening in systematic reviews. We are grateful for their support and assistance.