How to search PubMed and use filters

This section is about how to find evidence by performing a PubMed search. As a general principle, we have listed sources that are open access and freely available.

PubMed: Coverage

PubMed is a free database available at http://www.pubmed.gov/. It is maintained by the United States National Library of Medicine (NLM). It primarily includes the MEDLINE database, plus "Ahead of Print" citations that precede the article's final publication in a MEDLINE indexed journal and some older references to journals before they were indexed in MEDLINE. It indexes over 5,600 biomedical and life science journals and contains over 22.6 million references dating back to 1946.

PubMed citations often include links to the free full-text article in PubMed Central (PMC). PMC is a free full-text archive of biomedical and life sciences journals and currently archives over 2.7 million articles.

How to search

Simple subject search: Be as specific as possible and use no punctuation or Boolean operators. First identify the key concepts for your search. When you enter the terms (or key concepts) in the search box, suggestions will display in the search window as you type your search terms. You can see how PubMed interprets your search in the Search Details window on right hand sidebar of screen. You can edit the search in the Query Translation box.

American and British spelling: Searches will retrieve the same citations regardless of whether the American or British spelling is used (eg. hypoglycemia or hypoglycaemia) because the PubMed mapping feature “translates” users' queries with British spellings into American spellings behind the scenes – as shown in the Search Details window. If you retrieve too many citations, some ways to limit the number of search results are:

  • Replace general search terms with more specific ones (e.g. diabetes with type 2 diabetes)
  • Add additional terms to your search
  • Use the sidebar filters to restrict your results by publication dates, article types, language etc.

Searching by author: Enter the author’s last name plus initials without punctuation in the search box, (e.g. holman r) and then click Search.

Searching by author and subject: Use the authors last name and initials and the subject – no need to use the AND operator, eg holman r basal insulin

How to find a specific citation: If you have some information (such as the author, journal name and the year the article was published) and want the full citation information, then click the Single Citation Matcher from the PubMed homepage and enter the information you have in the fill-in-the-blank boxes. PubMed will display the full citation details.

Guides to searching: Click here for the PubMed Quick Start guide or here for further tutorials and PubMed Online training

Using PubMed search filters

What is a search filter? Search filters are designed to help you retrieve the evidence you need amongst the millions of citations in the database. They are pre-tested strategies made up of search terms that are optimised for sensitivity and specificity against a known ‘gold standard’ of articles in the database.

Note: Methodological search filters are NOT a guarantee of retrieving quality research. The user still needs to appraise the evidence for quality, relevance and applicability.

There are two main ways to access search filters in PubMed, either via the Filters Sidebar or the Clinical Queries.

Using the Filters sidebar: The filters sidebar appears on the left hand of the results screen when you display the results of your PubMed search.

The default filters are Article Types, Text Availability, Publication Dates and Species, but others are available by clicking on the Show additional filters link.

Note: Using these filters may exclude "in process" and "supplied by publisher" citations because they have not yet completed the MEDLINE indexing process.

If you do further searches the filters will be retained, so remember to clear them if you no longer want them to apply.

Some examples of PubMed searches using filters:

Example 1. Find guidelines on the management of type 2 diabetes which are published in the last 5 years

  1. Go to the PubMed home page
  2. Type management of type 2 diabetes in the search window and click Search
  3. From the list of filters on the left sidebar, go to Article types and click on More….
  4. Scroll down the list of article types and select Guideline and then click Show. Guideline will now appear under Article types. To activate the guidelines filter, click on this term so it now changes to blue font with a tick (check mark) beside it.
  5. To limit to recent citations go to Publication dates and click on 5 years so it now changes to a blue font with a check mark .
  6. There are several ways to save your results. To email the results to yourself, click the check box to the left of the citations you want to save.
  7. Click Send to at the top of the page
  8. From the Choose destination window select E-mail
  9. You will them get a menu to choose the format etc and add your email address.

Note: These filters do not have perfect sensitivity and specificity, so not all relevant articles will be retrieved and not all retrieved will be relevant; therefore you will need to exercise your judgement to decide if they relevant to your needs.

Example 2. Find systematic reviews or meta-analyses on GLP-1 agonists, for which free full text is available.

  1. Select the Clear All link on the sidebar to remove all the filters from the previous search
  2. Type GLP-1 agonists in the search window and click Search
  3. From the list of filters on the left sidebar, go to Article types and click on More…. Scroll down the list of article types and select Meta-Analysis and also Systematic Reviews and then click Show. These terms will now appear under Article types. To activate them need to select them both so they appear in blue font with a tick (check mark) beside them.
  4. Under Text availability select Free full text available.

Note: You can also search for systematic reviews using the Clinical Queries feature

Example 3. Find recent randomized controlled trials on diabetic foot ulcers which are in English

  1. Select the Clear All link on the sidebar to remove all the filters from the previous search
  2. Type diabetic foot ulcers in the PubMed search window and press Search.
  3. From the list of filters on the left sidebar, go to Article types and click on More…. Scroll down the list of Article types and check Randomized controlled trial then click Show. This term will now appear under Article types. To activate the filter click on this term so it now appears in blue font with a tick (check mark) beside it.
  4. To limit the search by English language click on the link Show additional filters at the bottom of the sidebar. Check Languages, click on Show and then select English.

Example 4. Find articles on the adherence to insulin therapy in type 2 diabetes published since 2010

  1. Select the Clear All link on the sidebar to remove all the filters from the previous search
  2. Type adherence to insulin therapy in type 2 diabetes in the PubMed search window and press Search.
  3. From the list of filters on the left sidebar, go to Publication dates and click on Custom range
  4. A Custom date range box will appear. Type 2010 in the first box (where it has YYYY) and then click Apply to activate the limit.
  5. A box at the top of the screen will display the citations found by title matching your search (these are likely to be the most relevant if the words are in the title) and then underneath will be all of the results of your search.

PubMed Clinical Queries

The Clinical Queries feature is available under PubMed Tools from the PubMed home page or directly. It uses built in Research Methodology Filters based on search strategies are made up of search terms that relate to the methodology of study design. They are designed to retrieve levels of evidence (eg. systematic reviews) or types of clinical queries (e.g. diagnosis, prognosis, etiology, treatment etc) when combined with the subject search terms of your choice.

Example 5: Find journal articles on the diagnosis of gestational diabetes

  1. From the PubMed Clinical Queries window type in the search term gestational diabetes and click Search.
  2. You will now have the choice of two search windows with drop down menus to refine the search. a) Category: the options are: Therapy, Etiology, Diagnosis, Prognosis, Clinical Prediction Guides. b) Scope: the options are Broad or Narrow.
  3. From the Category window select Diagnosis and from Scope window select Narrow. (If you get too few references you can broaden the Scope by choosing Broad).

Note: The search also displays results a separate column of results for Systematic Reviews of gestational diabetes.

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