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Literature Searching

Searching for best evidence in the literature is a key component of evidence-informed public health.  Searching the literature is as much an art as it is a science.  The main approach to literature searching is using bibliographic databases to access the research literature.  However, other approaches to finding relevant literature are also important.


The steps to searching the research literature in bibliographic databases include:

  1. Defining the question
  2. Identifying search terms
  3. Developing the search strategy
  4. Selecting the databases
  5. Conducting the search
  6. Reviewing the results, and
  7. Managing the results.

Defining the Question

Conducting an effective literature search hinges on asking a good question.  The acronym PISCO will help you ask an answerable question. 

Population – Define the population of interest, such as animals, humans, males, females, age groups, etc.,

Intervention – These can be therapeutic, preventative, programmatic, managerial, economic, etc.,



Setting/Comparison – The setting is where the health concern or intervention takes place such as the community, schools, hospitals, Ontario, etc., or alternatively, a comparison can be made against another intervention,

Outcome – The expected results may include reductions or increases in symptoms, benefits, costs, events, prognosis, mortality, etc.

Framing your research question to include these concepts can help to reduce the number of irrelevant articles you retrieve while making sure you do not miss anything on topic. 

You may sometimes wish to omit outcomes as a concept, depending on your question and the breadth of outcomes for which you are looking, but in principle, you will use these main concepts to build your search strategy.  

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Identifying Search Terms

The main concepts making up your question can now be used to develop your search terms.

A simple technique is to create a table with a column for each main concept. In each of the columns, write down all the words and multi-word terms you can think of which convey that concept.



Setting/ Comparison






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Developing the Search Strategy

The search strategy is developed by combining the concepts and terms used to express those concepts.  To do this, most databases use the Boolean Operators: OR, AND, and NOT.


Combining terms with OR will retrieve results that contain any of the terms.  This will broaden the search.  Use OR to combine all the terms which convey the same concept.  Using the table, you will OR together all the terms within a single column.  

Example: to describe the concept of teenagers you would include the terms adolescent OR adolescents OR teenager OR teenagers OR teen OR teens OR youth OR youths


Combining terms with AND will retrieve results that contain all of the terms.  This will limit and focus the search.

Use AND to combine the different concepts.  Using the table, you will AND the columns together after the terms within each column have been OR-ed together.  

Example: In developing the concepts for evidence for the efficacy of school health fairs to address adolescent smoking, the concepts to AND together would include:

(adolescent OR adolescents OR teen OR teens OR teenager OR teenagers OR youth OR youths)


(“health fair” OR “health fairs” OR “health carnival” OR “health carnivals”)


(school OR schools)


(smoking OR smoke OR cigarette OR cigarettes OR tobacco OR cigar OR cigars)


Combining terms with NOT will retrieve results which contain the first term but not the second term.  Since it often eliminates articles that would be of interest, NOT should rarely be used.

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Selecting Databases 

After developing a search strategy select what databases you are going to search. Bibliographic databases are gateways into the research literature and as such, list articles from literally thousands of journals.  There are many different bibliographic databases, each with different subject areas and coverage.  Search those with subjects related to your search topic.  Public health is very inter-disciplinary so be ready to search databases not directly about health and medicine, such as sociology, environment, economic, and education databases.

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Conducting the Search

The developed search strategy is now ready to be put into the search boxes of the database. 

The details for searching different databases may be somewhat different because not all databases are created by the same company.  However all databases have some commonalities to keep in mind.

1.  Controlled Vocabulary

Some databases have controlled vocabulary, which is a thesaurus of set terms, one term for each concept.  Terms which best describe what an article is about are assigned to that article.  Controlled vocabulary can be added to your search terms to improve your search, just OR them with the other terms expressing the same concept.  By including controlled vocabulary, you can minimize the risk of missing a synonym in your keyword search.  To find the controlled vocabulary in a database look for menu items like: thesaurus, subject headings, subjects, subject terms, MeSH, headings, and index or indices.

2.  Search Fields

Most databases allow you to search in different fields including the abstract, article title, journal title, and author fields.  Typically by default, if no other field is selected, the database will search all of them.  This is generally the most comprehensive way to search but other options are available.

3.  Truncation Marks

Major databases typically all have truncation marks.  A truncation mark should be placed at the stem of a word.  The database will then retrieve all words with that stem.  In most databases, the truncation mark is an * (asterisk).  For example adolescen* will find adolescent, adolescents, and adolescence.

4.  Limits

Most databases also have pre-set limits you can set to further refine your search.  Some standard limits include language, publication year, and peer-reviewed journals only.  Limits can be very useful, just be sure you know what the limit is actually removing so you do not accidentally exclude useful articles.

5.  Help File

All databases will have some sort of help file or help section.  This section will explain the database’s interface, where different features are, what the search syntax is, and how to search the database effectively whether you are a beginner or advanced searcher.

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Reviewing your Results

Once you have conducted your search, look through the results that you are getting to see how relevant they are and how many there are.  Based upon these two factors, you will probably need to revise your search strategy.  If there are a lot of irrelevant results, look to see what part of the search is causing them to be retrieved and see if you can remove that part of the search without losing relevant results.  Also, look through the relevant results for any terms that you can add to the search to find more relevant results.  

Depending upon how broad or narrow the results are, you might need to revisit your initial search question and either broaden it or focus it more, then go through the searching process again.  You might also retrieve articles that involve different disciplines than you originally thought, leading you to search different information sources than originally planned.

The thing to remember is that there is no such thing as a perfect search and that the process is not linear.  The more comprehensive you want your search to be, the more irrelevant results you will get.  The more focussed your search, the more likely you are to exclude relevant articles.  You will have to find the appropriate balance for your particular information need.

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Managing your Results

Once you have settled on a final search strategy, you need to manage your results.  In most databases you can either select specific articles to export or export all of the results.  Exporting the results generally allows you to create a reference list in a word or text document or to input the citations into a reference management software if you have one, such as Endnote, RefWorks, or Reference Manager.  Some databases also allow for you to save the results right to a personal account within the database platform.  Once you have a saved list of the articles you want, you can begin looking for them in full text.  Some databases will have some full text right in the results, but for most articles you will need a subscription or copy of the journal or book.  If you do not have access to these, contact the library to request a copy. 

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Other Approaches to Literature Searching

Although searching bibliographic databases is the main source of relevant literature, it is still possible for literature to remain unidentified that is highly relevant to your search question.

Other means of finding relevant evidence includes:

  • Searching the reference lists of already identified research articles,
  • Hand searching relevant journals that may not be included in traditional bibliographic databases,
  • Consulting experts that may have attended conferences or involved in initiatives that address your question,
  • Searching for evidence that has not been traditionally published, commonly referred to as grey literature, and,
  • Searching the websites of professional organizations, institutions, associations and government agencies1

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A Word About Grey Literature

Grey literature is “that which is produced on all levels of government, academics, business and industry in print and electronic formats, but which is not controlled by commercial publishers.”2

It can be government publications, NGO white papers, technical standards, policy briefs, or university theses among many other things.  Information in the grey literature is often of high quality and reflective of current thinking not only from policy makers but of front line workers and the general public.  It often fills a gap in the published journal literature.  It is called grey literature because it is often hard to find.  Several publications that will help you understand and find grey literature include OPHLA’s Public Health Grey Literature Database and Public Health Grey Literature Sources (PDF, 125KB),  Grey Literature Report from the New York Academy of Medicine Library, and Grey Matters by the Canadian Agency for Drugs and Technologies in Health.

Date of creation: February 28, 2013
Last modified on: August 24, 2015




1Aveyard, H., & Sharp, P. (2009). Guide to evidence based practice in health and social care. New York: Open University Press.
2The New York Academy of Medicine Library. (n.d.). What is grey literature? Retrieved from