You cannot conduct a search with a full sentence in a bibliographic database, you need to breakdown your research question. 


Before starting your search, what are the main elements your research question?

Ask yourself: What do I need to know? How can I determine if something is relevant to my study or project?



Are helmets effective in preventing head injury for cyclists? 


What are the most essential elements to search? 

bicycles (The context of your question involves bicycles or people who ride them)

helmets (You want to know if helmets are effective)

head injury (You want to determine if helmets prevent head injury)


Keywords are words referred to as your natural language; words you developed to describe your topic or concepts. 

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 has 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" terms in a database that uses subject headings. Here are the “Used For” terms in the scope note (description) for the MeSH subject heading “Translational Medical Research”

Subject headings are pre-defined "controlled vocabulary" words used to describe the content or topic of a publication. Subject headings are selected by indexers from a list and assigned to an article. 

Each database uses its own subject headings - Medline's are called MeSH (Medical Subject Headings).



Keywords  MeSH Subject Heading

senior citizen
older adult
aging population




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

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. 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:

Wildcards substitute a symbol 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

Databases usually require phrases to be placed within double quotes, for example, kidney transplant”. Without the double quotes, the database will search for the words individually anywhere in the record.

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 are pre-defined 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.

BMJ Clinical Evidence Study Design Filters

CADTH's Search Filters to Identify Economic Evaluations
A group of search filters developed and tested using a gold standard set of economic evaluations and statistical analysis.

Clinical Queries in PubMed Search Page
Specialized PubMed searches intended for clinicians to limit retrieval to articles that report research conducted with specific methodologies. Clinical Queries in PubMed Tutorial

Cochrane Search Filters
The Cochrane Collaboration has developed highly sensitive search strategies for identifying randomized trials

InterTASC Information Specialists' Sub-Group Search Filter Resource
A collaborative venture to identify, assess and test search filters designed to retrieve research by study design or focus.

McMaster University Health Information Research Unit (HiRU) Hedges
Search filters developed and validated by researchers in HiRU are available for use on PubMed’s Clinical Queries page and Health Services Research Queries page, Ovid’s Additional Limits page for MEDLINE, Embase and PsycINFO; EBSCOhost’s main searching page for CINAHL; and HiRU’s Nephrology filters and Knowledge Translation (KT) filters.

More PubMed Topic Specific Queries
Starting point for all the PubMed special queries, including comparative effectiveness research, health services research, AIDS, health disparities and more.

Scottish Intercollegiate Guidelines Network (SIGN) Search Filters
SIGN has devised suitable strategies for search filters in Ovid Medline, Ovid Embase and CINAHL. Filter available include: Systematic Reviews, Randomized Controlled Trials, Observational Studies, Diagnostic Studies, Economic Studies, Patient issues.

You may have also set out other limits in your systematic review protocol such as date limits or age limits. We recommend that carry these out at the end of your search.

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.

Use Web of Science, Scopus or Google Scholar to link to the articles that have cited key articles.

Once you have created a search strategy, you can save the search history. You can save it within the database or set up email alerts of new publications based on your search strategy. Register for a personal account within the respective database to save your search history. 

Saving the search history can help:

Keep track of your searching methods important for publication

Provide a base to refine or improve the search strategy

Determine searches with the most relevant results


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.

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.

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 is also typically updated prior to being submitted for publication.

You may wish to check if any key articles have been retracted. Try searching Retraction Watch.

You can also limit the results in PubMed to retracted publications