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Systematic Reviews: Searching

Before You Begin.....

Minimizing bias in locating, selecting, coding and aggregating individual studies for a systematic review is essential. A systematic approach to searching the literature will help to identify all of the best available literature that addresses your specific clinical question.

  • Define your question, using the PICO(S) OR PCC model
  • Check for existing reviews / protocols that have already been published.
  • This helps to ensure that the work has not already been done and 
  • provides examples of search strategies for your topic.


Search Tips

1. Identify synonyms and related terms

Create a list of terms for each PICO OR PCC element to ensure the search retrieves as many relevant studies as possible

  • check search terms used in other similar reviews or papers
  • always use a combination of subject headings and text words(keywords)

2. Build a search strategy

Combine search terms identified for Patient, Intervention and Comparison. It is not usually necessary to include the Outcome in the search strategy

  • use OR to search for all synonyms for Patient, Intervention and Comparison
  • use AND to combine Patient AND Intervention (AND Comparison if required)

Remember the search strategy will not search the entire full text of articles - it only searches the subject headings and text words(keywords) in the abstract.

Or get rid of 2. and use simple image to show Boolean operators combining synonyms and PIC elements.

3. Truncate text words

All databases allow truncation to ensure retrieval of all possible variations of a word

eg. therap* wil find therapy, therapies, therapist, therapeutic, therapeutics

Each database uses a different truncation symbol so check the database help for details.

4. Use proximity operators

Proximity or adjacency searching allows you to specify the proximity of words to each other

eg. state adj wide will find state wide, statewide


Formulate an Answerable Question

Use the PICO model to develop a well-formulated question to guide the review process

Where to Search


Ensure you search a wide range of subject specific databases in order to capture the full extent of published journal literature on your topic. Databases all index a different set of journals, and while you can expect some overlap you will also find unique content in each database. 
Most subject areas will have specific core databases that the majority of systematic reviews will use, and then subject-specific databases depending on the topic.  
If you're not sure where to start, you can:

  • visit our major databases(see links below).
  • consult other systematic reviews to view the list of databases they have searched;
  • consult a Librarian.
  • in the health and medical sciences area consult the Cochrane Handbook chapter on searching for studies.


Supplementary search techniques may be used as part of your scoping searches, to locate a gold set of relevant articles for testing your search, or in order to develop a search strategy on a niche topic.  Citation searching is a search method that can be done forward or backward in time.

Forward citation searching retrieves records that have cited an item also known as "cited by".  This provides you with more recently published articles that may be relevant for your topic.

Backward citation searching involves records that an item has cited (these will be located in the article's reference list). This is also known as snowballing - using known relevant articles to identify other key articles  or search terms.
The main citation databases are Scopus, Web of Science and Google Scholar

Citations and references of key articles are an important supplementary source of published literature and will often help you to discover additional
studies that have not appeared in the search results of your database searches.

Using resources such as Google Scholar will make this a simple process. Search for a key article you already know of, and then use the database's functionality to link to citations and references for that article. 
PubMed PubReminer and OVID Reminer tools assist in finding additional specific and similar citations from your primary search results.
Trial Registers and repositories of results - Many of the clinical trial registers include information about trials that are in progress as well as those that have been completed.  Examples are in link below:

Clinical Trial Registry

Other reviews and guidelines - Some useful examples are:

Other desirable sources

Hand searching involves examining manually key journals, conference proceedings and other relevant publications page by page. Hand searching is to overcome deficiencies in indexing or database coverage. Conference proceedings are important to hand search because individual conference papers are rarely indexed.

Grey literature sources include reports, dissertations, theses etc. For information click on Grey literature tab above.

Citation indexes such as Web of Science and Scopus allow you to track literature over a period of time.

Individuals and organisations - relevant personnel and associations/societies/groups should be identified and tracked down for information about unpublished or ongoing studies for possible inclusion in reviews. 

Internet - An Internet search can identify websites of relevant organisations, companies, academic centres which can then be scanned for relevant research studies. It may be worthwhile to try more than one search engine as you can often get different results from different search engines even when using the same search. 

Search Filters

A search filter is a defined search strategy designed to find certain types of articles in a particular database.

Search filters may be designed to retrieve records using a specific study design, for example, randomised controlled trials or systematic reviews;  or on a specific subject. 

The following sites include examples of pre-tested search filters:

Cochrane Handbook - Section 6.4.11 
Filter for identifying RCTs

InterTASC Information Specialists' Sub-Group
The ISSG has developed a quality checklist to assess published filters designed to retrieve records by specific study design

Scottish Intercollegiate Guidelines Network (SIGN) Search Filters
SIGN has devised strategies for running each search filter in Ovid Medline and Embase, and CINAHL.

McMaster Hedges
McMaster University filters for diagnosis, therapy, prognosis, etiology/harm and economic analysis for Medline, Embase and PsycINFO

PubMed Clinical Queries Filters
These search strategies help find citations that correspond to a specific clinical study category.

BMJ Clinical Evidence
Study design search filters for Ovid Medline and Embase

PubMed Search Strategies Blog
This blog has been created to share PubMed search strategies.

Search filters for palliative care, heart failure, dementia, residential aged care and dementia.

Lowitja Institute
Filters for Aboriginal & Torres Strait Islander health literature.




Alerts are an effective means of keeping track of the latest research. Many databases and journals offer free alert services through emails and RSS feeds. Types of alerts include:

  • Search alerts -this is a saved search which alerts you when a book or article that matches your search terms is published
  • Table of Contents (TOC) alert, which provides the table of contents of a newly published issue of a particular journal - use Browzine
  • Citation alerts which let you know when a particular article is cited by a new article


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