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Systematic Reviews and Meta Analysis

A resource for finding data sources, filters, and standards to support systematic searches of the biomedical literature.

Data Sources

Databases You Will Probably Search

No one database can cover the literature for any topic. For medical topics, a combination of PubMed (or other search of PubMed data) plus Embase, Web of Science, and Google Scholar has been shown to provide adequate recall (Syst Rev. 2017;6(1):245). For topics that reach beyond the biomedicine, other databases need to be considered.

  • PubMed
    PubMed is both the search platform provided by the National Center for Biotechnology information and the database. PubMed includes MEDLINE (records indexed with MeSH terms) but also material in process, older records from before the inception of MEDLINE, and material from journals not included in MEDLINE. The PubMed database is available on independent platforms including Ovid SP, Web of Science, and several others.
  • Embase
    Note: Embase requires users to either create an individual account (free) or log in with an institutional email address to enable the export of records. Before you start a session, 'log in" at the upper right. You can either create an account or use your Harvard email (recommended).  Embase includes materials second tier European and Asian journals not included in MEDLINE as well as conference abstracts. The Emtree controlled vocabulary is well developed. Embase records include more Emtree terms than MEDLINE records do MeSH term. Hence, results sets can often be significantly large in Embase, especially for drug-related searches.
  • Cochrane Central Register of Controlled Trials
    Cochrane Central contains trials from both MEDLINE and Embase plus many trials from other, non-indexed sources; limited to randomized and non-randomized controlled trials.  MeSH for MEDLINE records, but no other controlled vocabulary. To limit to results in Central, click the "Trials" limit to the left of your results.
  • Web of Science Core Collection (includes the Science Citation Index)
    Broad coverage of all sciences.  Will cover some journals at the edge of the biomedical sciences missed by PubMed and Embase. Some meeting information. No controlled vocabulary. Alternatively, the Elsevier database Scopus can be used. Harvard does not license access to Scopus.
  • GoogleScholar
    Consider as a supplement to the literature databases. It can improve sensitivity because it searches the full-text of articles. Screening the first 200-400 records in a search is recommended.
  • ClinicalTrials.gov
    Registers trials that are recruiting, completed, or terminated. Some records includes results.  Searching here helps identify unpublished trials. See below for other registries.

These database can be an effective complement to your search.  They can be essential in their specialized topic areas.

  • BIOSIS Previews
    Although it is primarly useful for biologists, it contains a lot of meetings and some medical journals.  Controlled vocabulary is not suitable for medical searching.
  • CINAHL
    Nursing and other health related information; excellent source for issues in patient care.  Well developed controlled vocabulary.
  • PsycINFO
    Cognitive and behavioral therapies are well covered.  Controlled vocabulary.
  • Google Scholar
    Add as an additional source. Here are some search tips.
  • WHO Global Index Medicus
    Search all WHO regional indexes, including the South-East Asia and Western Pacific Pacific regional databases.
  • Sociological Abstracts
    The primary index for sociological literature.  May be useful for community-related studies or interpersonal issues. Controlled vocabulary.
  • 3ie Impact Evaluation Repository
    Investigating an ecomomic or social intervention? The 3ie Impact Evaluation Repository is a currated database for evidence of what works in international development in low- and middle-income countries.
  • EconLit
    Economics. Almost any social intervetion and many medical ones get studied by economists.
  • RePEc IDEAS
    A repository of economics literature. It includes bibliographic metadata from many archives.

Resources for Meetings and Other Grey Literature

Truely unbiased searches look for unpublished literature in a number of places, included meeting abstracts, white papers, clinical trial registries, and searching by hand.

  • GreyNet
    GreyNet is an organization dedicated to promoting and facilitating the use of grey literature. Includes of listing of grey literature resources, GreySource.  OpenGrey, a former multidisciplinary database of technical reports, meetings, dissertations, and official publications is now archived in GreyNet. 
  • Grey Literature Report
    A bi-monthly publication of the New York Academy of Medicine, the GLR includes listings of recently published reports in health science and public health. The archives are tagged with MeSH terms and are searchable.
  • BIOSIS Previews
    Meetings! BIOSIS Previews includes proceedings of many meetings that may not be electronically available elsewhere.
  • ProQuest Dissertations & Theses Global
    A central authoritative source for locating doctoral dissertations and master's theses. Provides full text for most indexed dissertations from 1990-present. Includes theses and dissertations from the Harvard T.H. Chan School of Public Health, Harvard Medical School, and Harvard School of Dental Medicine.
  • greylitsearcher
    A web-based tool for performing systematic and transparent searches of organizational websites

Identifying sources for grey literature and being sure you've done enough is a challenge. The Canadian Agency for Drugs and Technologies in Health (CADTH) feels your pain and has produced a checklist that might help guide your grey research. The Grey Matters checklist provides an organized source of health technology assessment sites, regulatory agencies, trial registries, and other databases in a form that can help ensure the completeness of you search.

Clinical Trial Registries

When you search Cochrane Library/Trials, you will see results from both ClinicalTrials.gov and ICTRP. 

More information about trial registries and solving the problems associated with searching them is available through this site:
Medical and health-related trials registers and research registers
which is maintained by Julie Glanville and Carol Lefebvre and hosted by the York Health Economics Health Consortium.

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