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Systematic Review Guide

Search Skills

Your search must be both comprehensive and replicable. In the appendix of your publication you should include a search strategy with sufficient detail that that it can be re-run reliably.

The first step is having a clearly defined question. Your PICO(S) should guide your choice of search concepts. Before you start, it is help to do some brainstorming of the various terms used to describe your topic.

Key Concepts

Before starting your search, ask yourself what are the key concepts of your question?

For example:

In people who ride bicycles (P), are helmets (I) effective in preventing head injury (O)?

The major concepts are: bicycles, helmets, head injury. What are all the words that describe these concepts?

Concept 1 Concept 2 Concept 3
  • bicycle/s
  • bicycling
  • cycling
  • cyclist/s
  • helmet/s
  • head protection
  • protective head gear
  • protective head device
  • head injury / head injuries
  • brain injury / brain injuries
  • concussion/s
  • craniocerebral trauma
  • skull fracture
  • traumatic brain injury
  • TBI

Keyword Searching

  • Keywords are words used within a text. Generally, keywords will search in the record’s title, abstract, author, subject heading fields but it varies according to the database.
  • Unlike Google, most databases will not give you search results with alternate spellings or related terms - the words you write are exactly what you get. The exception to this is PubMed and Web of Science which have a type of “smart search.”
  • Spend some time making lists of all the synonyms for your search concepts. Consider different spellings and word combinations. A good way to find keywords is to scan the titles and abstracts of key articles to see how your concept is described. It is very important to have a comprehensive list of keywords in emerging fields where the usage is not consistent.
  • For example, “knowledge translation”, “translational medicine”, “knowledge diffusion”, “knowledge mobilization”, "bench to bedside” are all terms that may be used for similar concepts.


Example: Keyword search in Ovid Medline



Another way to find synonyms is to check the "Used For" or  "Entry Terms" in a database that uses subject headings. These can be seen when you check the subject heading description.

Subject Headings

Subject headings are pre-defined "controlled vocabulary" words used to describe the content of each item. Subject headings are selected by indexers from a list and assigned to an article to make searching easier. Each database uses its own subject headings - Medline's are called MeSH (Medical Subject Headings).

Keywords MeSH Subject Heading
  • senior citizen
  • elderly
  • older adult
  • aging population
  • geriatric


When you use the subject heading you will capture articles about older people without having to search on all the many other words.


Subject Heading Tutorials


Using Subject headings in Ovid databases (focused on MeSH) (4 min 35)

Using Subject headings in CINAHL (3 min 32)

Boolean Operators

Boolean operators connect your search terms together to either narrow or broaden your set of results. The three basic Boolean operators are: AND, OR, and NOT. Boolean operators must often be capitalized.


Use AND in a search to narrow your results. AND means that that all search terms must be present in the search results

E.g.   bicycles AND helmets AND head injuries


Use OR in a search for similar concepts (synonyms) to broaden your results, so that ANY of your search terms can be present in the search results. Remember “OR is more”.

E.g.   bicycles OR cyclists OR cycling


Use NOT to exclude words from your search and narrow the results. NOT should be used with caution.

E.g.   cycling NOT motorcycles

Parentheses or Brackets

With longer sets of terms you will need to combine them using parentheses just like in math problems.

E.g.   (cyclists OR bicycles) AND (helmets OR “head protection”)


You can use truncation to expand your search and save time. In most databases this done by using an asterisk* at the end of the root word.

For example, child* will find results with the words:

  • child
  • child’s
  • children
  • children’s
  • childhood
  • childish 


Wildcards substitute a symbol (often a question mark) for one letter of a word. This is useful if a word is spelled in different ways, but still has the same meaning.

E.g.    colo?r  will find color, colour

Phrase Searching

A phrase search looks for two or more words as an exact phrase. Databases usually require phrases to be placed within double quotes, for example, “critical care. Without the double quotes, the database will search for the words individually anywhere in the record (i.e. as critical AND care).

Searching Specific Fields

Almost all databases allow you to search specific fields in the bibliographic record such as title, abstract, author, journal title. Searching specific fields such as title and abstract only can allow you to do a more focused search. Check the Advanced Search options if field searching is not available in the basic search.

Search Filters

  • Search filters are pre-defined search strategies that have been developed by experienced searchers to help answer specific clinical questions, limit to certain populations or study designs. Many of them are validated.
  • There are a wide variety of filters available. You would first run your search and then add the search filter to your strategy. If you decide to use a filter, be sure to cite it.
  • Below is a selection of links to search filters.

Cited Reference Searching

Also known as forward and backward citation searching or “snowball” searching, you can check for articles listed in the bibliographies of key articles to see if there are additional relevant studies. You can use Web of Science, Scopus, Web of Science or Google Scholar to link to the articles that have cited key articles.

Saving Search Strategies

Once you have created a search strategy, save it within the database so that you can re-run it later or set up alerts to email yourself new results on a regular schedule. You can do this by registering for a personal account within the respective database.

Keep the search history records so that you can document your work later.

Peer Review of Search Strategies

The Canadian Agency for Drugs and Technologies in Health (CADTH) Peer Review Checklist for Search Strategies (PRESS) is a checklist of items to aid in the assessment of electronic database search strategies. This checklist is recommended for use by librarians undertaking the peer review of systematic review search strategies. 

Keeping Current with Alerts

It is important to continuously monitor the literature for new studies on your topic. Once you have created a search strategy and saved it your personal account within the database, you can use it to run automatic updates or alerts to be sent to your email.

You can also set up table of contents alerts from specific journals.

Each database had a slightly different method for created accounts and alerts. See for example, the instructions for PubMed e-mail alerts.

Updating the Search

Depending on how long it is taking you to carry out the systematic review, you will need to update your literature search to include the latest evidence. If you have saved your search strategies in the respective databases, then it should not be difficult to re-run the search with new date limits. The literature search should be updated prior to being submitted for publication.

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