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Systematic Reviews- Legacy (2020-2022): Design and Conduct Literature Searches

Created by Health Science Librarians

Role of the librarian in this stage

When designing and conducting literature searches, a librarian can advise you on: 

  • How to create a search strategy with Boolean operators, database-specific syntax, subject headings, and appropriate keywords 
  • How to apply previously published systematic review search strategies to your current search
  • How to test your search strategy's performance 
  • How to translate a search strategy from one database's preferred structure and syntax to another

Contact HSL About Your Review

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Ready to start a systematic review? HSL Librarians can help!

Fill out the Systematic Review Request Form and the best-suited librarian will get back to you promptly. Our systematic review service is only available to faculty, staff, students, and others who are affiliated with UNC Chapel Hill.

Partner with a librarian

The goal of a systematic search is to retrieve all results that are relevant to your topic. Because systematic review searches can be quite extensive and retrieve large numbers of results, an important aspect of systematic searching is limiting the number of irrelevant results that need to be screened. Librarians are experts trained in literature searching and systematic review methodology. Partnering with a librarian will save you time and improve the quality of your review.

Documenting searches

Systematic review quality is highly dependent on the literature search(es) used to identify studies. To follow best practices for reporting search strategies, as well as increase reproducibility and transparency, you should document various elements of the literature search for your review. To make this process more clear, a statement and checklist for reporting literature searches has been developed and is available on PRISMA's website and can be found below.

At a minimum, certain elements should be documented and reported like where you searched like databases, including name (i.e., Scopus) and platform (i.e. Elsevier), websites, registries, and grey literature searched. In addition, this also may include citation searching and reaching out to experts in the field. Search strategies used in each database or source should be documented, along with any filters or limits, and dates searched. If a search has been updated or was built upon previous work, that should be noted as well. It is also helpful to document which search terms have been tested and decisions made for term inclusion or exclusion by the team. Last, any peer review process should be stated as well as the total number of records identified from each source and how deduplication was handled. 

If the search strategy for your systematic review is being created and run by your review team's librarian, the search documentation will be handled entirely by the librarian.

You can document search strategies in word processing software you are familiar with like Microsoft Word or Excel, or Google Docs or Sheets. A template, and separate example file, is provided below for convenience. 

*Some databases like PubMed are being continually updated with new technology and algorithms. This means that searches may retrieve different results than when originally run, even with the same filters, date limits, etc.

Precision vs. sensitivity

Systematic searches balance precision and sensitivity. Precise searches will retrieve some relevant results but have a high risk of missing relevant literature. Sensitive searches retrieve most of the relevant literature but will also retrieve a higher proportion of irrelevant results. As demonstrated by the image below, it is impossible to achieve high precision and high sensitivity at the same time. Librarians search in an iterative manner to refine results and achieve an ideal balance of precision and sensitivity.

precise vs sensitive searches using circles to represent each search and dots to represent literature. precise searches are in a small circle showing a high number of relevant articles inside the circle. Sensitive searches are inside a much larger circle showing a higher number dots representing relevant and irrelevant literature inside.

Image reused from the University of Toronto Libraries

Turn your research question into search terms

Use PICO or another question development framework to translate your research question into search terms. 

Element Example


Patient(s) / Population(s)


infants diagnosed with necrotizing enterocolitis (NEC)




early enteral re-feeding




 late enteral re-feeding




NEC recurrence

Gather synonyms

There are many different types of synonyms to consider including in systematic searches.

Terms with similar meaning:

  • Early enteral re-feeding
  • Early enteral nutrition

Terms that have different spellings:

  • Re-feeding
  • Refeeding


  • Necrotizing enterocolitis
  • NEC

Concepts described inconsistently:

  • Quality of life
  • Satisfaction

Broad versus specific terms:

  • Necrotizing enterocolitis
  • Enterocolitis

Keywords versus controlled-vocabulary:

  • Necrotizing enterocolitis
  • "Enterocolitis, Necrotizing"[Mesh]

Discipline-specific jargon:

  • Enteral nutrition
  • Force feeding

There are several resources to consider when searching for synonyms. Scanning the search results of preliminary searches may help you identify additional search terms. Wikipedia, or other encyclopedias, may be helpful when looking for additional terms. Other databases can also help you identify synonyms. For example, PubChem can be used to look up drugs to find additional names and chemical compounds.

Controlled vocabulary

Controlled vocabulary is a set of terminology assigned to citations to describe the content of each article. Many databases assign controlled vocabulary terms to citations, but their naming schema is often specific to each database. For example, the controlled vocabulary system searchable via PubMed is MeSH, or Medical Subject Headings. More information on searching MeSH can be found here.

Searching with controlled vocabulary can improve the relevancy of search results. Not all citations are indexed with controlled vocabulary terms, however, so it is important to combine controlled vocabulary searches with text word searches. For example, combining controlled vocabulary and text words in PubMed would look like this: ("Enterocolitis, Necrotizing"[Mesh] or necrotizing enterocolitis[tw] OR NEC[tw])

As mentioned above, databases with controlled vocabulary often use their own unique system. A listing of controlled vocabulary systems by database is shown below.

Database Controlled Vocabulary Indicated By Example

Medical Subject Headings (MeSH)

[MeSH] "Chronic Disease"[Mesh]
Embase EMTREE /exp 'chronic disease'/exp
CINAHL CINAHL Headings MH or MM (MH "Chronic Disease")
PsycINFO APA Thesaurus DE DE "Chronic Illness"
Sociological Abstracts Thesaurus of Sociological Indexing Terms MAINSUBJECT.EXACT MAINSUBJECT.EXACT("Chronic Illness")

Controlled vocabulary may be outdated and some database allow users to submit requests to update terminology.

Boolean operators

Boolean operators are used to combine terms in literature searches. Searches are typically organized using the Boolean operators OR or AND. OR is used to combine search terms for the same concept (ie, refeeding). AND is used to combine different concepts (ie, refeeding and necrotizing enterocolitis). An example of how Boolean operators can affect search retrieval is shown below. Using AND to combine the two search terms will only retrieve results where both terms are used. Using OR to combine the two search terms will retrieve results that use either term separately or both together. It is important to note that, generally speaking, when you are performing a literature search you are only searching the title, abstract, keywords and other citation data. You are not searching the full-text of the articles.

boolean operator example using a venn diagram. the venn diagram displaying a search combined using AND retrieves a small subset of results that use both terms together. The venn diagram displaying a search combined with OR retrieves either search term separately and both combined.

Choose databases

Databases can be multidisciplinary or subject specific. Choose the best databases for your research question. Databases index various journals, so in order to be comprehensive, it is important to search multiple databases when conducting a systematic review. Consider searching databases with more diverse or global coverage (ie, Global Index Medicus) when appropriate. A list of popular databases is provided below. You can access UNC Libraries' full listing of databases on the HSL website (arranged alphabetically or by subject).

Translating searches to other databases

Databases often use their own set of terminology and syntax. When searching multiple databases, you need to adjust the search slightly to retrieve comparable results. Resources to help with this process are listed below.

Hand searching

Literature searches can be supplemented by hand searching. One of the most popular ways this is done with systematic reviews is by searching the reference list and citing articles of studies included in the review. Another method is manually browsing key journals in your field to make sure no relevant articles were missed. Other sources that may be considered for hand searching include: clinical trial registries, white papers and other reports, pharmaceutical or other corporate reports, conference proceedings, theses and dissertations, or professional association guidelines.

Grey literature

Grey literature typically refers to literature not published in a traditional manner and often not retrievable through large databases and other popular resources. Grey literature should be searched for inclusion in systematic reviews in order to reduce bias and increase thoroughness. There are several databases specific to grey literature that can be searched.

Search filters and hedges

Search hedges are search strategies or filters that have been expertly developed, or at times validated, for sensitivity and precision. Search hedges can be incorporated into your search to save time and improve efficiency. Search hedges, also know as filters, are not the same as the general filters found in various databases. Search hedges should be used carefully as they are database specific.