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Library Research FAQ

FAQ and introduction to using A.T. Still Memorial Library for online research and learning

Introduction to Literature Searching

Literature searching can seem daunting at first, especially if you haven't done it before (or haven't done it in a while). This page will introduce you to some of the essential information you need to know on how to search for literature in academic databases such as PubMed or Still OneSearch. 

Note that is only meant to be a brief introduction to get you started. As searching experts, the librarians are always happy to help you understand searching, refine your search strategies, and help you find the information you need for research projects or to answer clinical questions.

Define Your Research Question

A well-formulated research question:

  • starts your entire search process
  • provides focus for your searches
  • guides the selection of literature sources

Your question should not be so narrow that you can't find any articles related to the topic, but shouldn't be so broad that it will be impossible for you to synthesize the current research. 

You do need to know a little bit about your topic to begin formulating a question. If you think you have a topic you'd like to focus on, do a quick literature search to start!

  • This will help you understand what types of research is already being done on the topic and what is trending in the subject area.
  • It can also help you start identifying keywords, MeSH terms, or subject terms so you can begin planning your search strategy. 

PICO is the framework most commonly used in Evidence-Based Practice to structure clinical questions, adjusted to fit the specific type of question.

  • Patient Problem or Population
  • Intervention
  • Comparison or Control
  • Outcome

The question types are: Therapy/Treatment, Prevention, Diagnosis, Prognosis, and Etiology

Create a Database Search Strategy based on PICO

Note: This type of strategy works for larger databases such as PubMedCochrane Library, etc. Smaller useful banks of evidence such as the ADA Evidence Database or the UK National Institute for Health & Care Excellence (NICE) may be more suitable for category browsing.

  1. Record but Do NOT search for your complete PICO sentence
  2. Identify key terms
  3. Identify any synonyms or broader terms that closely relate to your terms if applicable
    1. Find useful synonyms by browsing articles that match your search for their listed keywords, by consulting a thesaurus, by consulting your textbooks' glossaries or indices, or by searching a medical thesaurus such as PubMed's MeSH database
  4. Leave out adjectives, connecting words, punctuation, etc.
  5. Leave out any words that can be implied by other search terms
  6. Use Boolean coding (AND OR NOT) and punctuation to structure your search
    1. To get fewer results:
      1. Add more terms using Boolean code AND to limit your search
    2. To get more results:
      1. Remove terms to expand your search 
      2. Add synonyms for your terms using Boolean punctuation and Boolean code OR

PICO Question : For patients with halitosis [Patient Problem], are probiotics [Intervention] as effective as chlorhexidine mouthwash [Comparison] in reducing measurable Volatile Sulfer Compound levels [Outcome]?

Identify Important Keywords : halitosis, probiotics, chlorhexidine, mouthwash, volatile sulfur compound

Simple PubMed Search : halitosis AND probiotics AND sulfur

The Boolean connector AND tells the database that all articles you find must include each of those words. 

Sulfur is unique enough that it is useful to try searching without the rest of the phrase first. If you find too many irrelevant articles, then add the entire phrase.

This search finds less than 20 articles, many of which appear relevant. This may be a good point to browse abstracts to find the best articles, or to find further useful specific terms to further narrow your question or search. 

Pubmed Search Part Two : halitosis AND sulfur AND chlorhexidine

In this case, you can better organize and consider your search results by running a new but related searches. 

Run a new search to find the same sort of articles focused on chlorhexidine mouthwash.  Ideally, you will be able to find the data necessary to perform a thorough analysis in the two sets of results.

PICO Question: In adolescent athletes [Patient Population], does the use of facial protection [Intervention] reduce the risk of maxillofacial injury [Outcome]?

Note: Prevention or prognosis questions sometimes do not include a specific Comparison or Control aspect.

Identify Important Keywords: adolescent, athletes, facial protection, maxillofacial injuries

Simple PubMed Search: athletes AND "maxillofacial injuries" AND "facial protection"

For this search, you want to make sure that it looks for the phrases maxillofacial injuries and facial protection, and not just those several words in any position in the article, so you must enclose them in quotation marks. This will always tell a database that you want to find exactly the enclosed phrase.

This search finds only one article. You must broaden your search. You can do this by dropping off one of your terms, which will mean that you find more articles. Or, you can do it by adding more synonyms for some of the terms:

Pubmed Search Part Two : athletes AND "maxillofacial injuries" AND ("facial protection" OR mouthguard OR "mouth guard" OR "face mask" OR "face guard" OR "Mouth Protectors")

Facial protection is a broad category term that isn't very commonly used, so it is a good choice to consider for adding synonyms to your search. You can find useful synonyms or names of specific types of facial protection by browsing articles that match your search, consulting a thesaurus, or by searching a medical thesaurus such as PubMed's MeSH database.

Adding the Boolean code word OR in between terms means that you will find all articles that contain either or both terms; the parentheses ensure that the AND part of the search is unaffected. 

Changing your search this way quadruples your useful search results.

Pubmed Search Part Threeathletes AND ("maxillofacial injuries" OR "jaw injuries" OR "jaw fractures" OR maxillofacial fractures" OR  "dental fracture" OR "mandibular fracture") AND ("facial protection" OR mouthguard OR "mouth guard" OR "face mask" OR "face guard" OR "Mouth Protectors")

Maxillofacial injuries is also a good term to expand upon - while it is more standard than facial protection, it has many subcategories or variants.

This nearly doubles your search results.

PubMed Search Part Four: athletes AND ("maxillofacial injuries" OR "jaw injuries" OR "jaw fractures" OR maxillofacial fractures" OR  "dental fracture" OR "mandibular fracture") AND ("facial protection" OR mouthguard OR "mouth guard" OR "face mask" OR "face guard" OR "Mouth Protectors") , with the addition of the Ages : Adolescent : 13-18 years filter

Use one of the filters on the left side of the screen to limit your results to your desired population age, or alternatively, manually add it as an AND term. 

This will reduce your results to only those directly applicable to your query.

Search for Articles Using Boolean Operators

Boolean operators are the core of a successful and targeted literature search. Boolean operators are three simple operators you can use to connect your search terms and instruct the database on how to look for literature in a way that fits your research question.


  • use AND in between search terms to tell the database that your results must include both terms. This is a great way to narrow your results down if you are retrieving too many non-relevant articles.
  • Use AND to connect the concepts in your question together.
  • Ex: If you want to search for articles on diabetes in children, you would search for diabetes AND children


  • Use OR in between search terms to tell the database that your results can include either or both of the search terms.
  • Use OR to connect synonyms and related concepts to get a more thorough search
  • Ex. To get a full search for all child populations you would search for children OR youth OR minors 


  • Use NOT to tell the database that you do not want articles including a search term within your results.
  • This can be used to exclude things irrelevant to your research, such as certain populations.
  • Ex. If we wanted to search for children but not teens you could search for children NOT teens



Advanced Search Techniques

There are three more important search techniques vital to developing a good search string. These techniques are used to structure your search and get exactly the results you need.

  • Parentheses
    • Use parentheses to group terms and tell the database what combination you want to search for and in what order. This is similar to algebraic expressions.
    • This is how you combine different types of boolean operators and structure you search in line with your research question
    • For example (children OR youth) AND (diabetes OR obesity) would first search the elements in parentheses, and then combine the results of those two searches with an AND
  • Quotation Marks
    • Use quotation marks around a phrase to tell the database to search for those exact words in that exact order. This is required whenever you are searching for a phrase instead of just a single keywords.
    • Ex. "mental health"
  • Wildcards/Truncation
    • Use * to tell the database to search all terms that start with a particular string of letters. For example, pharm* would search for pharmacology, pharmaceuticals, pharmacologists, and more.
    • This is a great way to expand your search without doing more typing

((healthcare OR "health care") AND ethics) NOT nurses

  • As an example, the above search string would search for articles including either healthcare or health care and the word ethics, and exclude every article mentioning nurses.

Field Tags

Field tags are used to tell a database where it is searching for your keywords. In most cases, you will want to search the titles and abstracts of articles for your keywords. Using field tags is equivalent to using dropdown menus in databases to limit your search, such as in the screenshot below, which shows using the dropdown to search only in the titles of articles in Still OneSearch.

Each database has its own way of forming field tags, so it is best to look at the help documentation of the database you are using or reach out to a librarian for help. As an example, using field tags in PubMed is shown below.

Field tags in PubMed are formed by putting letters in brackets after a term. For example, the field tag for searching in the titles and abstracts in PubMed is [tiab]. To search for the term diabetes in the title and abstracts of articles in PubMed, we would search for diabetes[tiab]. A full list of field tags in PubMed can be found on the PubMed help page

Using Subject Headings

Subject headings, also known as thesauri, controlled vocabularies, or taxonomies, are a set of specific and controlled terms applied to research articles to clearly mark what topics a research article addresses.  Subject headings:

  • Are used to help researchers find all relevant articles on a particular topic
  • Search for all articles on a topic regardless of variations in terminology
  • Are a predefined set of words developed by database vendors and professional indexers

As an example, let's look at MeSH, the subject heading system used by PubMed. The MeSH term Drug Therapy is used for any articles that reference drug therapy, drug therapies, chemotherapy, chemotherapies, pharmacotherapy, and pharmacotherapies. So when you are using PubMed, you can do a search for the subject heading Drug Therapy to get comprehensive results, even if the author was using the alternative terminology listed above.

Subject headings are a great way to get a comprehensive search without thinking of every possible synonym or language variation on your own, which also makes them ideal for quick searches on specific topics.

To use subject headings:

  • Find a way to browse a particular database's subject headings, such as the MeSH browser for PubMed 
  • Do keyword searches to look for relevant subject headings
  • Click on subject headings of interest and read their scope notes/documentation to make sure it is what you need
  • Add them to your search with boolean operators and with the correct field tags to identify them as subject headings

Note that every database uses its own subject headings system. When using a new database, try looking for terms such as Subject Headings, Index Terms, or Thesaurus in its navigation or help menus to find their subject headings. Database help or support pages may also provide guidance on using subject headings.

Develop a chart of search terms

Turning a research question into a search string is a multi-stepped process:

  1. Break down your research question into searchable concepts
  2. Write down a list of keywords and synonyms for each concept
  3. Map each concept to relevant controlled vocabularies for each database (such as MeSH)

As you do test searches and read more relevant literature, you will be able to add additional keywords to your search concepts. It is recommended that you reach out to a librarian for assistance in generating keywords and mapping concepts to a controlled vocabulary.

Example Research question: Does obesity lead to heart disease and strokes?

Topic Keywords
Natural language
Subject Headings
Academic Search Complete
Subject Terms
obesity obesity
morbidly obese
"Obesity, Morbid"[Mesh]
(MH "Obesity")
(MH "Obesity, Morbid")
DE "MORBID obesity"
heart disease heart disease
cardiac diseases
heart disorders
"Heart Diseases"[Mesh] (MH "Heart Diseases") DE "HEART diseases"
stroke stroke
cerebrovascular accidents
"Stroke"[Mesh] (MH "Stroke") DE "STROKE"

Build your Search

Once all terms have been identified, you need to put them together in a search string. You can export your search strategy in addition to the results, to use in your search documentation.

A search string will generally look like:

(Topic A term 1 OR Topic A term 2) AND (Topic B term 1 OR Topic B term 2) AND (Topic C term 1 OR Topic C term 2)

If searching PubMed with our example research question, the search string would look like:

(obesity OR overweight OR obese OR "morbidly obese" OR "Obesity"[Mesh] OR "Obesity, Morbid"[Mesh]) AND ("heart disease" OR "cardiac diseases" OR "heart disorders" OR cardiovascular OR "Heart Diseases"[Mesh]) AND (stroke OR "cerebrovascular accidents" OR "Stroke"[Mesh])

The search string above was developed for PubMed. When adapting the string for another database, you want to have the strings operate as similarly as possible. You would replace the MeSH terms with the controlled vocabulary of the other databases used.

The search string above is searching with both keywords and MeSH terms. The MeSH terms will be searched in the MeSH field. The keywords will be searched in all fields, like the title, abstract, journal name, etc.