Overview & Steps for Searching the Literature

Literature searching and literature reviews are often used interchangeably but are two different steps in the research process guided by EBM.

  • Literature search is searching the literature for some studies. A search strategy is developed for one or more biomedical databases to search the literature, and gather relevant studies.
  • Literature review is reviewing the studies which have been identified through a literature search. As part of the literature review, the retrieved articles are analyzed and critically appraised. 

The following steps will help guide you through the process of literature searching in PubMed. Though we are focusing on PubMed, these steps can be used across bibliographic databases. 

  1. Formulate a research question
  2. Identify primary concepts & gather synonyms
  3. Locate Medical Subject Headings MeSH (database-specific indexing terms)
  4. Combine search terms using Boolean operators
  5. Apply search limits or filters

To learn more about the literature searching process, you can explore Lane Library's Literature Searching guide.

Step 1: Formulate a Research Question

The first step in literature searching involves taking a clinical topic or problem and formulating it into a well-defined, answerable question. The development of a clear and focused question will help to streamline the searching process to locate the literature needed to begin answering the question and addressing the clinical problem. A well-defined, answerable question: 

  • defines the focus of your literature search
  • identifies the appropriate study design and methods
  • makes searching for evidence simpler and more effective
  • helps you identify relevant results and separate relevant results from irrelevant ones

What type of question are you asking?

  • Therapy: effectiveness/risk of a certain treatment

  • Diagnosis: accuracy/usefulness of a diagnostic test/tool; application to a specific patient 

  • Prognosis: probable outcome, progression, or survivability of a disease or condition; likelihood of occurrence

  • Etiology/Harm: cause or risk factors for a disease or condition; questions about the harmful effect of an intervention or exposure on a patient

Tips for formulating a good question:

  • The question is directly relevant to the most important health issue for the patient;
  • The question is focused and when answered, will help the patient the most;
  • The question is phrased to facilitate a targeted literature search for precise answers

Adopted from CEBM: what makes a good clinical question and Center for Evidence Based Medicine: Asking focused questions 

PICO Framework

In EBM, following the PICO framework is a common way to create a focused and answerable question from a general topic. PICO is a mnemonic used to describe the four elements of a sound clinical foreground question.

PICO  stands for:

  • P - Population/Patient/Problem
  • I - Intervention  
  • C - Comparison or Control
  • O - Outcome

Alternative formats of PICO include PICOT and PICOTT:

  • T - Time
  • T - Type of question
  • T - Type of study


What is the effectiveness of Prozac vs Zoloft in treating adolescents with depression?

P: adolescents with depression

I: Prozac

C: Zoloft

O: n/a

Using PICO to formulate your research question makes it easier to follow the next step in the literature searching process -- identifying primary concepts & gathering synonyms.

Step 2: Identify Primary Concepts & Gather Synonyms

Primary concepts for your research question can be identified using the PICO formula from Step 1. Each of the PICO elements can form a primary concept. If your PICO does not have a Comparison or Outcome, or if the Outcome is broad or vague, it is okay to leave out these concepts. Sometimes, one of the elements in the PICO framework will include more than one primary concept. For example, the Population for our example includes the concept of adolescents and the concept of depression.


Padolescents with depression



O: n/a

For each primary concept identified, make a list of other terms with the same or related meaning (synonyms). It is important to gather synonyms, because

  • Terms have different spellings, plural forms, and acronyms

  • Concepts are described inconsistently across time, geographies, or even among researchers

  • Terms have the same/close meaning, disciplinary jargon

  • Umbrella terms vs specific names for issues, interventions, or concepts

These terms will form the keywords of your search strategy. 


Concepts Synonyms
adolescents teen, teens, teenager, adolescence, youth
depression depressive, depressions
Prozac fluoxetine, fluoxetin, sarafem
Zoloft sertraline, altruline, lustral, sealdin, gladem

Tips for finding synonyms:

  • Do a quick search to find a relevant article or two. Look at the words used in the article titles and abstracts.
  • Think of specific examples or types
  • Use background information to help brainstorm (e.g. UpToDate, DynaMed, textbooks)
  • Explore the entry terms and related subject headings in MeSH (see Step 3)

Remember that building a search strategy is iterative. As you learn more about your topic, you can add more keywords to your search to broaden your results, or remove keywords if you are finding too many results.

Step 3: Locate Medical Subject Headings MeSH (database-specific indexing terms)

What is Mesh?

Databases like PubMed use subject headings or controlled vocabularies to index (or label) articles. Subject headings are standardized terms for describing what the articles are about. Subject headings are specific to databases, and in PubMed, they are called Medical Subject Headings or MeSH. MeSH terms are structured hierarchically in a tree structure, and when you search a MeSH term, you search automatically includes all the terms that fall beneath it in the tree. Indexers add MeSH terms to journal article records in PubMed to reflect their subject content. 

MeSH terms are useful in a search to aid in locating synonyms and reduce term ambiguities. It facilitates the retrieval of relevant articles even when authors use different words or spelling to describe the same concept. For instance, using the MeSH term "Blood Pressure" will also find articles that use "pulse pressure," "diastolic pressure," and "systolic pressure."

Screenshot of Mesh record for Blood Pressure with entry terms circled in red

Since MeSH terms are organized in hierarchies or MeSH trees, it also facilitates the searching for broad and narrow concepts. For instance, the MeSH term "Domestic Violence" will retrieve articles containing narrower topics such as "child abuse," "elder abuse," and "spouse abuse." But you can also expand the search, and move to a broader level, such as "Violence."

Mesh tree for Domestic Violence

To look up a MeSH term, click on "MeSH Database" on PubMed's homepage. Type your concept into the search bar. The MeSH database will return appropriate MeSH (terms) if there are any. Not every concept will have a matching MeSH term. Remember to search for one concept at a time.

Mesh search interface with the search bar circled in red


adolescents => "Adolescent"[Mesh]

Prozac => "Fluoxetine"[Mesh]

Zoloft => "Sertraline"[Mesh]

depression => "Depression"[Mesh]

When you search for a MeSH term in PubMed, use the [Mesh] tag following your search term to specify where to search for the term in the PubMed record.

You can also locate MeSH terms in PubMed by finding a relevant article and scrolling to the heading "MeSH terms" at the bottom of the article. This only works for articles that have been indexed. 

Screenshot of the References and Mesh section of a PubMed articles record with the Mesh terms circled in red

Other PubMed Search Tags

In addition to searching specifically for MeSH terms, you can also use search tags to search for keywords in particular fields of the PubMed record. When you search in PubMed, you are automatically looking for your keywords in all the record fields. Sometimes this might be too broad and bring back too many search results. You can experiment with field tags like [ti] to look for keywords only in the title or [tiab] to look for keywords only in the title or abstract. Explore all of the available search tags and reach out to your liaison librarian if you have questions using search tags.

Step 4: Combine Search Terms Using Boolean Operators

Now that you've identified keywords for your concepts (step 2) and related MeSH terms (step 3), you can combine your search terms with Boolean Operators to build your search strategy.

Boolean Operators are a set of commands that can be used in almost every search engine, database, or online catalog to provide more focus to a search. The most basic Boolean commands are AND and OR. In PubMed, you can use Boolean Operators to combine search terms, and narrow or broaden a set of results.

Narrow Results with AND

Use AND in a search to narrow your results. It tells the search engine to return results that contain ALL the search terms in a record.

two intersecting circles with the overlap shaded to demonstrate how the AND Boolean operator works


adolescents AND depression

Note: Both the words adolescents and depression will be present in every record in the results.

Broaden Results with OR

Use OR in a search to broaden your results by connecting similar concepts (synonyms). It tells the search engine to return results that contain ANY of the search terms in a record.

two intersecting circles completely shaded to demonstrate the OR Boolean operator


adolescents OR youth OR teenagers

Note: Search results need to have at least one of the words adolescents or youth or teenagers.


Use parentheses ( ) to keep concepts that are alike together, and to tell the database to look for search terms in the parentheses first. It is particularly important when you use the Boolean Operator “OR”.


(adolescents OR youth OR teenagers) AND depression

Tip: You can use"Advanced Search" option in PubMed to help build your search strategy. Search concept by concept, adding ORs between all your keywords and MeSH terms for each concept. After you complete a search for each concept, you can use the "Actions" menu in the Advance Search Search History table to add combine your concept searches with AND. This will look for the overlap between your concept searches and help you avoid nesting errors.

Full Search Strategy Example:

("Adolescent"[Mesh] OR adolescent OR teen OR teens OR teenager OR youth OR youths) AND ("Depression"[Mesh] OR depressive OR depression) AND ("Fluoxetine"[Mesh] OR prozac OR fluoxetin* OR sarafem) AND ("Sertraline"[Mesh] OR zoloft OR sertraline OR altruline OR lustral OR sealdin OR gladem)

Step 5: Apply Search Limits or Filters

You can filter your search results using the PubMed filters in the left sidebar. You can filter by study type to look for the highest level of evidence to answer your question. You can also use date filters or filter to English language materials. If the study type you are looking for is not listed, select "Additional Filters" at the bottom of the left sidebar to see all the available options.

Note: Many PubMed filters depend on indexing, and using filters will exclude articles that do not have indexing.


screenshot of PubMed filters with red arrow pointing at Additional Filters button

You can also try PubMed's Clinical Queries to narrow your search results to the type of clinical questions you are asking (Therapy, Diagnosis, etc.).

Getting Too Many Results?

If your search retrieves too many results, you can limit the search results by

  • replacing general (e.g. vague or broad) terms with more specific ones
  • including additional concepts in your search
  • using PubMed's sidebar filters on the left panel of the results page to restrict results by publication date, article type, population, and more

Getting Too Few Results?

If your search returns too few results, you can expand your search by

  • browsing the Similar Articles on the abstract page for a citation to see closely related articles generated by PubMed's algorithm
  • Removing specific or extraneous terms from the search string
  • Using alternative terms to describe a similar concept used in the search


Databases to Search Journal Articles

Useful Websites and Handouts

Literature Searching Handouts and Checklist

Evidence-Based Research Organizations & Repositories

Lane Classes and Tutorials