Psychological & Brain Sciences for Graduate Students

PICO is an acronym to help you break down your clinical question in order to identify clearly what evidence you need to find. You can use this to create keywords for your searches.

• Patient, Population, Problem: What are the most important characteristics of this patient? What subset of the patient? What subset of the patient population are you researching? What specific condition or disease are you addressing? 

• Intervention, Prognostic Factor, Exposure: Which intervention prognostic factor, or exposure are you considering?

• Comparison: What is the main alternative to compare with the intervention (note: research question may not include a comparison)

• Outcome: What do you hope to accomplish, measure, improve or affect? 

Setting up the Search

• Create a search strategy by identifying essential search concepts from PICO question 

• Brainstorm synonyms/related terms for each PICO search concept

• Determine PICO question type and which study design is the best evidence to answer it 

Example

A parent of a 5-year old child reports that the child is squinting and shutting one eye to focus in on an object. Child is diagnosed with amblyopia. 

• Patient, Population, Problem: Child with amblyopia.

• Intervention, Prognostic Factor, Exposure: Wearing an eye patch on the stronger eye

• Comparison: Eye drops for the stronger eye

• Outcome: Strengthening weaker eye 

PICO Boolean Search

This search provides the basic components of a search: 

P: amblyopia 

AND

I: eye patch

AND 

C: eye drops 

However, we want to ensure other related terms are included to capture a robust search, so the search could also include these terms:

P: amblyopia OR "lazy eye" 

AND

I: eye patch

AND 

C: eye drops

Searching in PubMed

Here is how you can structure your search in PubMed. Note that "lazy eye" is in quotation marks, which locks in the exact phrasing. Eye patch and eye drops were not put into quotation marks because it would limit the search by looking only for eye patch rather than eye patches and same with eye drops.

PubMed

PubMed is a free resource that provides access to more than 36 million citations for biomedical literature from MEDLINE, life science journals, and online books. Users can search, explore, download, and find full text articles. PubMed is freely available, but access to full-text articles will depend on institutional access. For example, since you are an affiliate of IU, you will have access to many full-text articles through PubMed.

PubMed Central (PMC) is a free full-text archive of biomedical and life sciences journal literature at the U.S. National Institutes of Health's National Library of Medicine (NIH/NLM). Unlike PubMed proper, all of articles in PMC are available in full-text. If you don't have institutional affiliation, this can be a great tool to search for full-text biomedical research. 

Searching in PubMed

Each database will have its own search structure and controlled vocabulary. Understanding how PubMed is retrieving information can be helpful for structuring a successful search string. 

MeSH

Records in PubMed have been assigned subject headings, a controlled vocabulary called Medical Subject Headings or MeSH for short. These are used to index citations allowing you to retrieve all records on a particular subject regardless of the terminology used by the author. For example, a search for the subject heading Amblyopia will retrieve records that include terms such as lazy eye, anisometropic amblyopia, and suppression amblyopia. The MeSH term also includes any variant spellings and plurals. 

A simple PubMed search automatically searches for MeSH terms. However, you can also carry out your own searches using the MeSH database if you wish.

• MeSH database

  MeSH (Medical Subject Headings) is the NLM controlled vocabulary thesaurus used for indexing citations in MEDLINE and PubMed. When searching PubMed, and limiting the search to MeSH, only MEDLINE citations will be retrieved.

Example

If we use the PICO example above and run the search and click "advanced" and then details, you'll see the following entry

This detailed snapshot provides an overview of which terms were used and how they were applied in PubMed. The translation section breaks your search into major concepts: amblyopia, lazy eye, eye, patch, and eye drops. Some of these concepts may look duplicative, for example, in the amblyopia section, PubMed is searching "amblyopia"[MeSH Terms] OR "amblyopia" [All Fields].

Why are both terms included?

When searching for literature, it is important to use both MeSH terms and textwords. This is because not all articles, especially those that are recently published, have been assigned MeSH terms. To ensure you are finding the most recent literature, combining MeSH terms with all fields will result in a more comprehensive set of articles.

"amblyopia"[MeSH Terms]

OR

"amblyopia" [All Fields]

Automatic Term Mapping (ATM)

Automatic Term Mapping (ATM) is a process that happens in the background of most PubMed searches.  The database takes the terms that you have entered into the search box and attempts to interpret them and map them to the appropriate MeSH Terms.

In most everyday or casual searches, the ATM feature will help your search by not requiring you to put as many terms into the search box or build more complex search queries. 

However, sometimes the ATM process can go in an unexpected or undesired direction.  So it is important to understand roughly how the database is interpreting your search, how to investigate any issues, and how to potentially turn this feature off or otherwise control it.

To learn more about ATM, check out the link below.

• How PubMed Works: Automatic Term Mapping

Refining Search Terms

Use any of the PubMed search tips and tricks below to refine your search terms. 

• Field tags to tell the database where to search

  • [tiab] = title & abstract

  • [tw] = textword = title, abstract, author provided keywords and few other fields

  • [mesh] = Medical Subject Heading

  • [au] = author

• Truncation - to search for all terms that begin with a word, enter the word followed by an asterisk (*) 

  • At least four characters must be provided in the truncated term

  • “Mobile health app*” = mobile health app, mobile health apps, mobile health application, etc.

• Phrase searching - to search for a specific phrase, enclose the phrase in double-quotes (" ")

  • “Mobile health technology”

  • Not all terms can be searched as a phrase

• All field tags (except [mesh]) and truncation terminate “automatic term mapping” function which maps the search terms to the corresponding MeSH terms and synonyms

• Nesting - use parentheses ( ) to keep concepts that are alike together,

  • diabetes AND (mobile health app OR telemedicine OR Mhealth)

• If you get “zero” result, check the spelling!

TL;DR

PubMed uses automatic term mapping to grab relevant MeSH headings as well as general keywords to search. It can be helpful to know how these search strategies are used in case something unexpected is being returned. You can also create your own search using just MeSH terms, just keywords, or a combination of both of them. One thing to note, automatic term mapping will search for keywords in all fields, which includes the author's name, title, abstract, etc. If you're looking to tailor your search, using the field tags above can be applied to be more specific.

Hierarchy of Evidence

Not all research is created the same. The pyramid above is used to illustrate the amount if information that's available as it relates to clinical studies. Most of the information found at the bottom of the pyramid relates to animal and lab studies. As you move up the pyramid, study designs use more rigorous methodologies and therefore reduce the level of potential bias. Studies toward the top of the pyramid are useful for clinical practice, but are fewer in number. Evidence-based practice involves finding the highest level of evidence based on the type of question asked. 

Type of Question