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Systematic and Scoping Reviews Search Methodology

Search Techniques

Several search techniques are common to a variety of licensed databases - subject headings, truncation, Boolean operators, and limits. Depending on your topic, there may also be search filters available to apply to one or more databases.  See these Medline Ovid tutorials for an overview of different techniques.

Techniques to aid the process include using a table in Word or Excel to list the concepts in your research question.  This way you can keep track of potentially relevant subject headings and keywords that you discover when exploring scope notes and thesaurus trees. Another is to use the save search history in most licensed databases to record your search and to set up email alerts for when new articles are found on your topic.

Subject Headings

Many databases include a system of subject headings (which may also be called descriptors). These terms are added to articles by human indexers to make it easier to search for all the articles on a particular concept.   Most other topical, or subject, databases have a system of subject headings, which can usually be found in the thesaurus section of a database. In Medline these are known as MeSH (Medical Subject Headings), in EMBASE as Emtree, and in CINAHL they are Headings.

Keywords

For a thorough literature search, you should search each concept with both keywords and subject headings.

Some databases and grey literature sources only allow searching by keyword, or natural language. Useful techniques include shortcuts, phrase searching and proximity searching:

Shortcuts to search for different spellings

Most databases use wildcards (or symbols) to replace 0 or more letters at the end, or in the middle of words.

For zero or more letters at the end of the word (eg for plural forms, tenses, adverbs etc.),  use the truncation symbol. In most topical databases this is the asterisk *.  It is added to the stem of a word.

  • Example: child* searches for child, child's, children, childhood... anything that begins with "child".
  • Note: The UBC Library catalogue uses the question mark ? as its truncation symbol

For zero or 1 letter in the middle of the word ( eg for British vs North American spelling), use the hash # or question mark ?, depending on the operating system of the search engine

  • Example: P?ediatric or colo?r in Ovid databases; P#ediatric or colo#r in Ebsco databases

For exactly one letter, either within or at the end of a word, use the hash # or question mark ?, depending on the operating system of the search engine.

  • Example: Wom#n in Ovid databases; Wom?n in Ebsco databases
  • Note: it is useful to use at the end of the word where the truncation symbol * may cause unnecessary confusion. For example: arm# in Ovid, or arm? in Ebsco, will find arms as well as army but it will avoid armament, armadillo etc that arm* would find.

Phrase searching

Most databases support searching for exact phrases by putting words in quotes

  • Example: "step down unit"

Proximity, or adjacency, searching

Many databases provide this ability to find more relevant results by an operator to define the relationship between words. The operator symbol differs between operating systems. Ovid databases use ADJ# and Ebsco databases use N# or W#

  • Example: social adj3 support (in Ovid) and social N3 support (in Ebsco) will find the words social and support within 3 words of each other

Tip: Check the help section of the database you're using to find out which of these features are available and how to use them.

Tutorials and Handouts

Boolean Operators

Boolean operators are useful for combining subject headings and keywords.

 

  • Example: Stroke AND balance finds articles with both these concepts
  • Example: Stroke OR CVA finds articles that include either or both concepts

NOT is another operator which will find one concept while excluding another. Use with caution because you may exclude relevant articles this way. See the document below for tips.

Limit or Refine

Most databases include various limiters. These usually qualify human characteristics such as gender, ethnicity or age or publication characteristics such as language, publication date, study design, or type of publication. 

Consult with a librarian about using limits in a systematic review search - it's easy to lose relevant articles when adding limits. 

One way to limit to human studies in Ovid MEDLINE is to combine this line with the last set of your search:

NOT (exp animals/ NOT (exp animals/ AND humans/)

How and when to use study type filters from Countway Library of Medicine, Harvard http://guides.library.harvard.edu/c.php?g=309982&p=2070466

Example Ovid MEDLINE Search Strategy

This document shows a sample search strategy and explains it with reference to the PICO model.

Phrase Searching in Ovid Databases

In general, quotation marks are not needed in order to search for words as a phrase in Ovid databases. However, one exception is when a phrase contains the word "use," which is a command in Ovid. You'll need to put a phrase containing use, or the word use by itself, in quotes in order to avoid an error message. 

Also, if a phrase in Ovid includes one of these words: and, as, for, from, is, of, that, the, this, to, was, were

Ovid will ignore the word in the phrase. This may cause you to find many more results than intended, in particular if you're searching for an exact phrase. Solution - use truncation on that word in your phrase:

"treatment as* prevention"

"female to* male"

See the link below for more details.

Search Filters

Search filters are pre-tested strategies used to find evidence in the medical databases that meets given criteria. They are often used to locate a specific type of study, such as a randomized controlled trial or a qualitative study. Use search filters to increase the chance of finding relevant materials.