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Systematic Reviews: Searching

Summary of steps in a systematic review literature search

  1. Select a framework (PICO, SPIDER etc).
  2. Using the framework design a researchable question. Record inclusion and exclusion criteria.
  3. Identify free text terms and subject headings relevant to each concept in your framework. Generate related terms and synonyms for free text terms. Ensure your search terms are consistent with your research question.
  4. Conduct a scoping search across one database to identify additional subject terms or free text terms. 
  5. Decide: Which search terms will be truncated, will wild cards,proximity operators or phrase searching be used? This will create your search statement for each concept in your table.
  6. Decide if a date and/or language restriction will be applied to search results. Ideally no language restrictions should be applied.
  7. Select a database for searching and decide which fields will be searched for results.
  8. Conduct a comprehensive search for each separate concept in your framework using  its search statement and selected fields.Apply boolean operators appropriately to combine terms within each search statement.
  9.  Utilize the search history and/or appropriate boolean operators to combine the completed searches for each of the separate concepts from the your selected framework in the selected database.
  10. Apply database limiting commands (date, study types). Decide if search filters are required.
  11. Export results to your reference manager.
  12. Save a record of the search.Note the platform used and the date of the search.

 

Conduct searches across multiple relevant databases (usually in health at least Medline, Embase and the Cochrane library are searched). Adapt searches to the characteristics of the database. Document any modifications when adapting your search to a new database e.g. Are the fields different? Does the database use different subject headings? Conduct supplementary searches across grey literature, as well as  hand searching selected journals and by citation tracking to address bias from published results. ​Whenever possible consult with a librarian in regard to your search strategy, online tutorials and guidelines are available.

Kugley,S., Wade, A., Thomas,J., Mahood,Q., Jorgensen, K., & Hammerstrom, N.S.(2015). Searching for studies: A guide for information retrieval for Campbell Systematic Reviews.Campbell Methods Guide 2016:1 doi: 10.4073/cmg.2016.1

 

PRECISION vs SENSITIVITY

When searching for material for systematic reviews there is a tension between comprehensiveness (SENSITIVITY) and relevance (PRECISION). In general the more comprehensive the search the less relevant are the results.  

​SENSITIVITY =  number of relevant reports identified/Total number of relevant reports in existence

​PRECISION =    number of relevant reports identified/Total number of reports identified (Cochrane Handbook for Systematic Reviews of Interventions).

 

​Developing a search strategy is an iterative process. Search terms are modified, based on what has already been retrieved. There are diminishing returns for search efforts; after a certain stage, each additional unit of time invested in searching returns fewer references that are relevant to the review. The decision as to how much to invest in the search process may depend on several factors, such as the question a review addresses, and the resources that are available.

Recommended sources

Databases used for the systematic review searching will vary according to the topic of the Systematic Review. Some of the major databases  used for health research are listed below.

Embase: European database of biomedical and pharmacologic literature.

Cochrane Library: Includes information on the effects of interventions in health care.

Joanna Briggs Institute EBP (JBI)Provides evidence in various formats for nursing, allied health and medical professionals.

Scopusislink opens in a newwindThislink opens in a new windo​: Access to peer-reviewed titles in health, sciences, engineering, social sciences, psychology, and economics.

CINAHL Plus with Full Text: A collection of full text for nursing & allied health journals. 

  Ovid Medline All: Includes the most complete version of Ovid MEDLINE.

PsycINFO (a.k.a PsycNET): Resource for abstracts of scholarly journal articles, book chapters, books, and dissertations. 

See other discipline Subject Guides for more databases: Medicine, Psychology, Nursing and Midwifery,Social Work and Community, Health Science.

Systematically searching grey literature

A 2015 paper by Godin et al  discusses a systematic process for searching grey literature that involves a combination of 4 different search strategies. These include  "(1) grey literature databases, (2) customized Google search engines, (3) targeted websites, and (4) consultation with contact experts" (p.1). See the paper here for more details on the process and documentation.

Godin, K., Stapleton, J., Kirkpatrick, S. I., Hanning, R. M., & Leatherdale, S. T. (2015). Applying systematic review search methods to the grey literature: a case study examining guidelines for school-based breakfast programs in Canada. Systematic reviews4(1), 138. http://10.1186/s13643-015-0125-0

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Grey literature

Images shows a number of different sized gear cogs working together. Inside the cogs are images of different ideas that might contribute to research

Systematic review literature searching requires detailed and documented searches across all relevant material. Publication bias can be mitigated by ensuring grey literature has also been thoroughly searched. 

 

Grey Literature is information that is published by organizations whose primary task is not publication, e.g. government departments. Searching grey literature is one way to address potential bias in reporting of research results via published material. It can be a daunting task so search those resources that make the most sense for your research question. Here is a list of some grey literature sources and databases.

Check also relevant government departments and peak organizational webpages.

Filters and Hedges

Hedges or filters are pre-designed search strategies for finding particular research study designs or topics. Using a search filter or hedge can save you time. Some filters or hedges have been tested for validity but it is always important for you to review and assess the appropriateness of particular filters to your research project. Below are some well-known sources of filters and hedges.

ISSG search filters resource

SIGN (Scottish Intercollegiate Guidelines Network) search filters

CADTH

Center for Evidence-Based Management (CEBMa)

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