Skip to Main Content
Go to Penn Libraries homepage   Go to Guides homepage

Systematic Reviews: Literature Search

This guide is intended to provide related information for the users who prepare to write systematic reviews.

Tips for Finding Databases

  •  Ulrich’s (global series directory) – to check where a journal is indexed
  • Journal Citation Reports (e.g. PubsHub, Web of Science) - to find out the journals with impact factor and other criteria on a particular subject
  •  Library guides on a subject of interest
  • Other systematic review – check the Methodology part to find out the databases searched for that particular topic
  • Database vendors web pages, e.g. EBSCO, OVID
  • Google  (topic AND database)

Grey Literature

  •  Definition 

1997- The Luxembourg Convention on Grey Literature;  expanded New York 2004
“...that which is produced on all levels of government, academics, business and industry in print and electronic formats, but which is not controlled by commercial publishers i.e. where publishing is not the main activity of the producing body”

  • Formats

Conference Abstract
Dissertation & Thesis
Registered Trial
White paper
Book Chapter

  •  Why search grey literature

Reduce publication bias
More access to global literature
Often more current

  • Types of grey literature

Clinical trial registries
Regulatory Information
Conference proceedings
Unpublished studies
Studies reported in languages other than English

  • Resources for grey literature 

·         Campus guide on grey literature

·         NYAM grey literature report  

         Canada’s federal HTA agency

Overview of Literature Search

• To reduce bias, multiple databases need to be searched

• Suggested main databases to be searched in health care field
      -Cochrane Library

• Search specialized databases or websites for your topic additional to the suggested main databases

• Search scientific information packets, e.g., manufactures of products under review, for specific topics 

• Search cited references of main literature search results

 •Hand search in targeted journals

• Keep personal communications (e.g., principal investigators, colleagues, authors, experts in a discipline) to get subject experts' opinions on resources and search strategies

• Conduct Google/Google Scholar search to find additional documents

•Search strategy may be influenced by inclusion and exclusion criteria

•Search grey literature

Search Terms

Techniques for harvesting terms

  •  Supplied by investigator
  • Identified in database records
    - Terms or phrases identified from a controlled vocabulary system within a particular database
    - Terms or phrases identified from preliminary search results in a relevant database
    - Terms or phrases identified from the search strategies of other systematic reviews on the topic

One technique of collecting terms in PubMed

  •  Identify the concepts in your search topic and list each in the term collection form
  •  Find MeSH terms, text words and phrases associated with that particular concept and list them in the term collection form
     - MeSH Browser could help to identify relevant MeSH terms
  •  For each concept, perform searches by combining MeSH with text words and phrases associated with that concept
  • Generate preliminary search results by combining all concepts search sets with appropriate boolean operators
  •  Exam results, looking for MeSH that reflect concepts, looking in title and abstract for author-generated terms that reflect the concepts
  •  List all the new MeSH terms and text words and phrases into the term collection form
  • Conduct a refined search by using all the relevant MeSH terms and text words and phrases identified in your first round search and the preliminary search results
  • Continue this circle until no new significantly relevant terms generated in your refined searches 

Methodology Filters

Methodology filters can help to get rid of undesirable study designs so as to reduce the size of a large retrieval. However systematic review attempts to maximize sensitivity in terms of retrieving all relevant documents. Therefore it is always preferable not to employ filters.

Sometimes retrieval sets are literally unmanageable. You‘d probably want to implement a methodology filter.

If you have to limit, use at all possible validated filters, which have been tested against gold-standard sets of bibliographic records. 

Iteration of Search

•Develop search strategies
- Identify appropriate search resources
- Collect search terms
- Adopt applicable search field qualifiers
- Utilize methodology filters
- Combine all search terms in a logical way
•Refine search strategies
•Communicate with PI or research team
•Update search

Signal of Stopping Search

•Keep revising your search strategies based on results got along the way
•When the last two or three searches in a database did not generate a significant number of new records, it might be the time to stop

Other guides

Search Tips

Penn Libraries Home Franklin Home
(215) 898-7555