Performing searches

Search multiple databases

Each database or platform provides access to different collections of resources. Searching multiple databases can help ensure you don’t miss out on crucial studies. When searching across multiple databases, remember:

Search each database separately

  • Each database contains different journals, uses different syntax and subject headings, and should therefore be searched separately.
  • Do not select multiple databases and search them simultaneously.
  • Do not rerun a search created on one database (e.g. Medline) in another one (e.g. Embase).

Use subject headings and keywords

  • Some databases, such as Scopus, use only keywords. However, many medicine and health databases, including as Medline and Embase, use a combination of keywords and subject headings. 
  • Subject headings are a controlled vocabulary assigned to articles to describe their content. To get the best results, your search strategy should include both keywords and subject headings.
  • Keywords can be used across multiple databases, but subject headings are specific to individual databases. This means you’ll need to adapt your search strategy to fit each database you search. See Flinders University's guide to translating searches across multiple databases.

Use syntax

  • Syntax search operators can be used to modify and improve the results of keyword searches. They will vary according to the database. 
  • See Flinders University's database syntax guide for a comprehensive table of operators used across different databases.

Database search guides

The “right number” of results

There is no magic number of search results that a comprehensive search should retrieve. The number of results will vary depending on the topic and the area of study. For example, established fields will find more results, while new fields will yield less. 

A comprehensive search strategy must be: 

  • inclusive enough to capture as many relevant results as possible 
  • specific enough to keep irrelevant results to a minimum.

If your search returns too few results:

  • include more synonyms for your keywords
  • add broader subject headings and/or use the “explode” function in Ovid databases, which selects a subject heading and all of its subheadings
  • reduce the number of main concepts in your search
  • use the Boolean operator “OR” to include more relevant words or concepts.

If your search returns too many results:

  • be more selective with your subject headings (if you have used the “explode” function, try removing it)
  • add more main concepts
  • remove or replace keywords with particularly broad or ambiguous meanings
  • use the Boolean operator “NOT” to exclude irrelevant words or concepts.

Check your search results

To ensure your search is working correctly and retrieving relevant results:

  • Find a small sample of relevant articles (5–10) using Google Scholar or PubMed and check if your search retrieved them
  • Identify additional search terms and subject headings using the PubMed PubReMiner. This tool will also identify relevant journals that can be used when handsearching. 

When to stop searching

When conducting a systematic review, you must search enough databases to confidently state that all relevant literature has been found. You will need to run each search multiple times to refine it. 

When running an iterative comprehensive search, you will reach a point where you see the same key citations appear in each set of results, meaning further refinements of the search are unnecessary. This is called a saturation point. 

Indicators of saturation include:

  • Your searches don’t find any “new” results.
  • You identify no new data.

Document your searches

  • Include a PRISMA flow diagram in your methods section, along with the search strategies themselves. 
  • Record your database search strategies in a document to refer to when writing up your methodology. 
  • Save your searches in whichever platform you are using to access your databases (e.g. Ovid, EBSCO).
  • Keep track of how many records were obtained from each database. You can do this by creating folders or groups in your reference manager. 

Refer to the Cochrane Handbook for tips on which elements of your search need to be documented.

Use EndNote

Create an EndNote library to organise references and facilitate the screening process for your systematic review. 

The following fields are directly extractable from EndNote library records: 

  • database name and platform
  • export date
  • number of results from each database
  • duplicates found.

Create an EndNote group for each database you search. Use groups to:

  • track the number of references exported from each database and how many were selected at each stage of the screening process
  • organise the stages of the systematic review process such as searching, search updates, and screening 
  • report numbers in the PRISMA flow diagram.

Additional search methods 

To ensure that you’ve located all relevant studies, consider supplementing your comprehensive search with one or more of the following search methods:

Handsearching 

Search specific journals that apply to your research area. Journals selected for handsearching should be identified from your database searches (Aromataris & Riitano, 2014; Booth, 2016) or a tool like PubReMiner.

Contacting authors

Contact authors of conference papers or relevant studies to clarify details of a study or request more data. They may also provide papers that weren't retrieved through your comprehensive search (Aromataris & Riitano, 2014; Booth, 2016).

Citation chaining 

Review the reference lists of articles you have already found to identify additional papers. If your comprehensive search finds a systematic review, look at its references to include the studies it reviews. 

Grey literature 

Searching grey literature is crucial for capturing unpublished studies.

Studies that are located by any of these methods (including grey literature) should be recorded in the “identified through other sources” box in your PRISMA flow diagram.

Rerun database searches

Many publishers will ask you to rerun your search if six months or more has lapsed between the last search and the date of submission. 

  1. Rerun your saved searches
  2. Filter results just for the last year to identify any new relevant articles
  3. Update your PRISMA flow diagram accordingly. 

Refer to this document for instructions on how to use EndNote to manage references when rerunning systematic review searches:

  • Related information

    Systematic reviews Planning your search Screening results

  • Contact

    For more help with planning and performing searches:

    Contact the Library Speak to a librarian