Literature searching and literature reviews are often used interchangeably but are two different steps in the research process guided by EBM.
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.
To learn more about the literature searching process, you can explore Lane Library's Literature Searching guide.
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:
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
Adopted from CEBM: what makes a good clinical question and Center for Evidence Based Medicine: Asking focused questions
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:
Alternative formats of PICO include PICOT and PICOTT:
What is the effectiveness of Prozac vs Zoloft in treating adolescents with depression?
P: adolescents with depression
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.
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.
P: adolescents with depression
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.
|adolescents||teen, teens, teenager, adolescence, youth|
|Prozac||fluoxetine, fluoxetin, sarafem|
|Zoloft||sertraline, altruline, lustral, sealdin, gladem|
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.
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."
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."
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.
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.
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.
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.
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.
adolescents AND depression
Note: Both the words adolescents and depression will be present in every record in the results.
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.
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.
("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)
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.
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.).
If your search retrieves too many results, you can limit the search results by
If your search returns too few results, you can expand your search by