Evidence Synthesis (Systematic Reviews)

Literature searches for evidence synthesis are different than literature searches for narrative reviews or other types of research. A quality evidence synthesis literature search is: 

• Comprehensive - You want to find as many relevant studies as possible. This requires searching across multiple databases and using a combination of keywords and controlled vocabulary (e.g. MeSH in Medline or PubMed, EMTREE in Embase...)
• Transparent - you will need to document your search strategies for each resource so that others know how you found your evidence.
• Replicable - You will likely have to update your searches before publishing, or at regular intervals for publications like clinical practice guidelines, which need to stay current.

The information presented below is a very basic overview of this process.

If you don't have any one on your team who has done a search like this, contact your subject librarian! 

• Controlled Vocabulary - a standardized set of terms used to categorize and retrieve information
  • PubMed: Medical Subject Headings (MeSH)
  • EMBASE: Emtree Thesaurus
  • CINAHL: Cinahl Headings
• Keywords - terms used by authors to describe concepts
• Truncation - a symbol (*) added to the end of the term to capture alternate endings
  • EX: genetic* = genetic, genetics, genetically
• Phrase searching - put terms in quotation marks to search them as a phrase
  • EX: "heart attack" 
• Field searching - searching terms in specified parts of the database record. This command will vary depending on which database you are searching.
  • EX: "heart attack"[Title/Abstract] or "heart attack"[tiab] searches for the phrase in the title and abstract of a PubMed record
  • EX: "heart attack":ti,ab  searches for the phrase in the title and abstract of an Embase record
  • EX: "myocardial infarction"[mesh] searches for the controlled (MeSH) term in PubMed
• Boolean Operators - logic commands used to combine search terms
  • OR  = expands retrieval, used to combine similar terms in a concept
    • lung OR pulmonary 
  • AND = limits retrieval; used to combine concepts 
    • lung AND cancer
  • NOT = limits retrieval by removing terms
    • lung NOT brain

• Parentheses - used to build a search with a combination of Boolean operators
  • EX: (lung OR pulmonary) AND (cancer OR neoplasm OR carcinoma)

Putting it together - an example of a PubMed search using all of the tools listed above:

 ("Lung Neoplasms"[Mesh] OR "lung cancer"[tiab] OR "lung neoplasm*"[tiab] OR "pulmonary cancer*"[tiab] OR "pulmonary neoplasm*"[tiab]) AND ("Immunotherapy"[Mesh] OR immunotherap*[tiab])

1. Start with your research question 

In patients with breast cancer, does practicing yoga reduce cancer related fatigue compared to other forms of exercise?

2. List out the main concepts of your question

Concept 1: Breast cancer 

Concept 2: Yoga

Concept 3: Fatigue

3. Identify the controlled vocabulary and keyword synonyms for each concept (Note: we are using PubMed syntax for this search)

Concept 1: Breast Neoplasms"[Mesh]; "breast cancer"; "breast neoplasms"; "mammary cancer"; "mammary neoplasms"; "breast carcinoma"...

Concept 2:  "Yoga"[Mesh]; yoga

Concept 3: "Fatigue"[Mesh]; fatigue; tired; tiredness; exhaustion; sleepy; sleepiness

4. Create a search strategy for each concept using the Boolean operator "OR" to combine similar terms. This is also the time to add truncation, phrases, and and fields 

Concept 1:

"Breast Neoplasms"[Mesh] OR "breast cancer*"[tiab] OR "breast neoplasm*"[tiab] OR "mammary cancer*"[tiab] OR "mammary neoplasm*"[tiab] OR "breast carcinoma*"[tiab]

Concept 2:

"Yoga"[Mesh] OR yoga[tiab]

Concept 3:  

"Fatigue"[Mesh] OR fatigue*[tiab] OR tired[tiab] OR tiredness[tiab] OR exhaustion[tiab] OR sleepy[tiab] OR sleepiness[tiab]

5. Combine the concepts using "AND"

You can put parenthesis around each concept and present the strategy in a single line:

("Breast Neoplasms"[Mesh] OR "breast cancer*"[tiab] OR "breast neoplasm*"[tiab] OR "mammary cancer*"[tiab] OR "mammary neoplasm*"[tiab] OR "breast carcinoma*"[tiab]) AND ("Yoga"[Mesh] OR yoga[tiab]) AND ("Fatigue"[Mesh] OR fatigue*[tiab] OR tired[tiab] OR tiredness[tiab] OR exhaustion[tiab] OR sleepy[tiab] OR sleepiness[tiab])

Or combine the search strings using the search numbers (here is a screenshot from PubMed)

6. Review your results and modify your search as necessary

 You may find additional terms to add to one or more of the concepts.  You may also notice that some terms are retrieving many irrelevant results and need to be removed or modified. You may go through this process many times before you find the right strategy. 

Most of the information for your evidence synthesis project will come from bibliographic databases of scholarly journal articles. There is no single database that indexes all of the literature on a topic so you should search AT LEAST three databases. The databases you choose depend on the topic areas covered in your research question. 

Subject area research guides are a good place to start when identifying databases and other potentially useful resources for your topic: Research Guides - Guides Home - Guides at Penn Libraries

Recommended Databases in the Health Sciences

• PubMed
  NLM's public access version to Medline, the premier database for biomedical literature.

Search Help: PubMed: Tips & Tricks - Guides at Pennn Libraries

• EMBASE 

Covers biomedical literature. Includes over 1,800 biomedical titles not offered by Medline/PubMed

Search help: How do I search in Embase? - Embase Support Center 

• Scopus 

Indexes journals in the sciences, social sciences, and arts and humanities. Allows for cited reference searching.

Search help: Scopus LibGuide - LibGuides at Elsevier 

• Web of Science 

Indexes journals in the sciences, social sciences, and arts and humanities. Allows for cited reference searching.

Search help: Web of Science Essentials 

• CINAHL/Nursing 

Indexes journal articles in nursing and allied health professions.

Search help: CINAHL Databases - Advance Searching Tutorial 

• APA PsycInfo 

Indexes literature in psychology and related fields.

Search help: Using APA PsycInfo - Psychology - Guides at Penn Libraries 

What is grey literature and why should I search for it?  

Grey literature refers to resources produced outside of commercial publishing. White papers, policies, reports, and registered clinical trials all fall under the umbrella of "Grey literature". Government organizations, businesses, professional associations, often produce grey literature. Grey literature may provide more current and/or detailed information than traditional published works and items cited in grey literature may provide additional studies for your report.

Resources for grey literature 

Penn Libraries Guide: Grey Literature in the Health Sciences