A Research Guide for Systematic Literature Reviews

Subject headings (or subject terms, index terms, etc.) are a controlled vocabulary used by databases in order to describe concepts and things. In modern terms, they're like hashtags. 

They are the organizational framework of databases (at least those databases that use them), and they can be used to precisely and systematically search those databases.

The two videos to the right cover the use of subject headings on PubMed. While the videos are specific to PubMed, they should capture the essence of subject heading searching and could be applicable to other databases that use subject headings (CINAHL Plus with Full Text, APA PsycINFO, ERIC, etc.). 

Nearly all databases/search engines include Boolean Operators. Understanding how they work is crucial to being an efficient searcher. 

AND:

• Narrows your search by combining two or more search terms.
• Example: Hypertension AND "DASH Diet" 
  • would retrieve articles about how the DASH diet can help to mitigate hypertension. 

OR: 

• Broadens your search by looking for either term. 
• Example: (Hypertension OR "high blood pressure") AND "DASH DIET" 
  • ​​​​​​​would retrieve articles about how the DASH diet can help to mitigate hypertension OR high blood pressure. 

NOT: 

• Narrows your search by specifically filtering out one (or more) search term
• Example: (Hypertension OR "high blood pressure") AND "DASH DIET" NOT diabetes 
  • ​​​​​​​would retrieve articles about how the DASH diet can help to mitigate hypertension OR high blood pressure (while ignoring articles that also mention diabetes). 

Using search fields effectively is an important step towards becoming an efficient searcher. 

Often the default search field will be something like "all fields" or "search everything." This search field will retrieve lots of results as it's looking for your keywords in any and every part of the article (title, abstract, full text, metadata, etc.). 

You can, however, choose more focused options. We'll provide screenshots with examples from a few databases. 

PubMed: In this case I'm searching for "DASH Diet" in either the title or abstract of the article, and for "hypertension" as a MeSH Major Topic. 

Scopus: Here we've used Scopus' TITLE-ABS-KEY field along with their AUTHOR-NAME field. 

Most databases have a "help" document of some sort - this is a good place to learn more about their search field options. 

Truncation (or "wildcard searching") is a way of searching for variable or branched spellings of search terms. 

In this case, searching for "Darwin*" means I am telling the database to search for the following terms: Darwin, Darwin's, Darwinian, Darwinism, etc. 

You can also sometimes place a wildcard in the middle of a term. You may use this if you have questions about how a certain word may be spelled (think "color" or "colour"). 

Remember to always check the "help" or "search tips" document in the database you are using. Some databases use truncation in different ways. 

Proximity searching is an extremely powerful search mechanic. 

In this case, by searching for "undergraduate n5 research" I am telling the database (ERIC) to find articles that have the search term "undergraduate" within 5 words of the search term "research" in the abstract. This can be a useful alternative to running a phrase search (putting quotations around a phrase). 

Remember to always check the "help" or "search tips" document in the database you are using. Some databases use proximity searching in different ways. 

Grey Literature includes sources that do not fall into "traditional" publishing categories: theses/dissertations, government documents/reports, white papers, patents, conference proceedings, newsletters, unpublished or unfinished clinical trials, etc. 

The 12th International Conference on Grey Literature (Prague, 2010) provided the following definition: 

"Grey literature stands for manifold document types produced on all levels of government, academics, business and industry in print and electronic formats that are protected by intellectual property rights, of sufficient quality to be collected and preserved by libraries and institutional repositories, but not controlled by commercial publishers; i.e. where publishing is not the primary activity of the producing body."

Using "site searching" can be a useful way of finding grey literature (especially government reports). 

Examples of site searching: 

• childhood obesity site:.gov (would only retrieve results from .gov sites). 
• childhood obesity site:nih.gov (would only retrieve results from The National Institutes of Health website)

Other Google resources that could be useful are linked below:

Handsearching important journals & reference tracking are ways of making sure that relevant articles do not fall through the cracks. 

Handsearching (or browsing) journals is recommended because some journals are not indexed in databases. 

Reference tracking can be done in low-tech (simply scanning reference lists of included articles) or high-tech (using citation tracking features on databases) ways. 

You might consult a librarian (or your reporting standards) to see if these methods are suitable for your review. At least one study has concluded that reference tracking is not an effective use of a review team's time. 

Below is a list of databases that provide reference tracking features: