“A comprehensive search forms the foundation of any systematic review and consists of writing specific search strategies in different online databases to retrieve eligible studies.” ¹

Selecting several databases ensures that your search is comprehensive. A well-cited guide on how to conduct a systematic review in medical research suggests, at a minimum, a combination of Embase, MEDLINE, Web of Science, and Google Scholar. Cochrane and Scopus are also common databases for biomedical systematic reviews.

• PubMed is the most common database to use. It is “a free resource supporting the search and retrieval of biomedical and life sciences literature”³ PubMed includes citations indexed in Medline, uploaded by journals, and archived in PubMed Central. The distinctions between PubMed, Medline, and PubMed Central are explained here.

• Embase is a subscription database maintained by Elsevier. It has comprehensive indexing and tagging of the biomedical literature.

• Web of Science is a subscription service run by Clarivate that indexes citations in several different science disciplines.

• Google Scholar allows the use of Google search techniques but restricts results to academic literature, including journal pages, PubMed, university pages, and pre-print archives. The comprehensive nature of sources Google draws from means that searches often return thousands of results, many of which are duplicates, making comprehensive screening of Google Scholar results difficult. Most sources are available in more structured databases, but Google Scholar can be advantageous to find pre-prints for new topics that have few published papers or for topics that fall outside of typical science disciplines.

• Cochrane contains many clinical trials, including some publications that are not indexed in PubMed. Cochrane can be searched without a subscription, but a subscription is necessary to download complete search results.

• Scopus is the largest abstract and citation database of peer-reviewed literature. It includes scientific journals, books, and conference proceedings.

• Psychology databases

• PsycINFO and CINAHL can be used “if the research question is related to the field of psychiatry, psychology and/or to nursing and allied health”. ¹
• PsycNet can also be used to search for “social and behavioral science content”²

• Consider consulting with a librarian for further help with your search.

Tips for building effective search terms can be found here. The best place to start when creating search terms is with the PICO (Population, Intervention, Control, and Outcome) elements identified during search planning. Common search terms include the condition of interest (ex. the disease)

Other search terms to consider include restrictions on publication date and language.

Boolean operators AND, OR, NOT can be used to specify the search further

• AND can be used to “narrow your results”¹ and “tell the database that ALL search terms must be present in the resulting records”⁵
• OR can be used to “connect two or more similar concepts”¹ and “broaden your results, telling the database that ANY of your search terms can be present in the resulting records”⁵
• NOT can be used to “exclude words from your search”¹ and “narrow your search, telling the database to ignore concepts that may be implied by your search terms”⁵

As you review your search results, take note of additional terminology and abbreviations used in these studies that could be included in the search terms to ensure relevant studies aren’t missed.

Finding Grey Literature

Metadata collected should include identifying information, such as DOI or PubMed ID, URL, author, and year, as well as information necessary for screening, such as title and abstract. If you are not using AutoLit, a system for removing duplicates and indicating screening status (i.e. included, excluded, or unscreened), exclusion reasons (ex. not relevant to the review topic, preclinical), and collecting full texts should be implemented.

1. Muka T, Glisic M, Milic J, et al. A 24-step guide on how to design, conduct, and successfully publish a systematic review and meta-analysis in medical research. CKGE_TMP_i Eur J Epidemiol CKGE_TMP_i . 2020;35(1):49-60. doi:10.1007/s10654-019-00576-5
2. APA PsycNet Overview. American Psychological Association. Accessed October 26, 2021. https://www.apa.org/pubs/databases/psycnet
3. PubMed Overview. National Library of Medicine. Accessed October 26, 2021. https://pubmed.ncbi.nlm.nih.gov/about/
4. Scopus: Access and use Support Center. Scopus. Updated July 29, 2021. Accessed October 26, 2021. https://service.elsevier.com/app/answers/detail/a_id/15534/supporthub/scopus/#tips
5. Database Search Tips: Boolean operators. MIT Libraries. Accessed October 28, 2021.https://libguides.mit.edu/c.php?g=175963&p=1158594